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Solid-Earth Sciences and Society (1993)

Chapter: 1 Global Overview

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Suggested Citation:"1 Global Overview." National Research Council. 1993. Solid-Earth Sciences and Society. Washington, DC: The National Academies Press. doi: 10.17226/1990.
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1
Global Overview

ESSAY ON THE EARTH SCIENCES

This is a particularly opportune time to assess the state of the earth sciences. New concepts arising from breakthroughs of the past quarter century as well as innovative technologies for gathering and organizing information are expanding the frontiers of knowledge about the earth system at an accelerating pace. Research ranges from the atomic scale of the scanning-tunneling microscope and ion microprobe to the global scale of worldwide seismic networks and images produced from data gathered by orbiting satellites. Earth scientists are constructing a comprehensive picture of the Earth, one that interrelates the physical, chemical, geological, and biological processes that characterize the planet and its history (Plate 1). Scientific advances and opportunities abound at the same time that environmental and resource problems affecting the world's population have become international political issues.

Human societies face momentous decisions in the next few years and decades. Issues such as atmospheric changes, nuclear power, hazardous wastes, environmental degradation, overpopulation, soil erosion, water quality and supplies, and the destruction of species cannot be ignored. The decisions eventually made about these environmental issues, including prediction of changes, must be based on reliable knowledge—knowledge that comes from understanding the earth system and its history.

Living on Earth

The more we have learned about the Earth, the more we have come to appreciate the many ways in which it is suited to life. The Earth is just the right distance from the Sun to have surface temperatures optimal to sustain living things. Its vast oceans have remained liquid, neither boiling into the atmosphere nor freezing into a solid block of ice, since shortly after its formation some 4.5-billion-years ago. It is the only planet in the

Suggested Citation:"1 Global Overview." National Research Council. 1993. Solid-Earth Sciences and Society. Washington, DC: The National Academies Press. doi: 10.17226/1990.
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solar system that exhibits plate tectonics, which recycles nutrients and other materials essential to life through the interior of the planet and back to the surface. The Earth is unique in sustaining an atmosphere that is one-fifth oxygen—oxygen that was generated over eons by single-celled organisms and that, in turn, spurred the evolution of multicellular organisms.

More particularly, the Earth is a congenial home for humans. All of the materials we use in our daily lives come from the Earth—fuels, minerals, groundwater, even our food (through the intermediaries of soil, water, and fertilizer). We have a strong psychological affinity for certain places on the Earth, for the regions where we grow up and live and for the wild and beautiful tracts, whether preserved in parks or apparent in our everyday surroundings. But we have altered the surface extensively during our occupation—erecting structures, clearing forests, damming rivers. Despite our activities, the Earth continues its normal path of inexorable change—through violent paroxysms such as earthquakes and landslides or through the slow, steady erosion of soils and coastlines.

The Earth is a resilient planet. Long after human beings have vanished from the planet, its basic cycles will persist. The largest man-made structures will erode and disappear, radioactive materials that have been gathered will decay, man-made concentrations of chemicals will disperse, and new species will evolve and perish. The oceans, atmosphere, solid-earth, and living things will continue to interact, just as they did before humans appeared on the scene.

But some earth systems are very fragile. We dispose of our wastes in the same sedimentary basins that supply us with the bulk of our groundwater, energy, and mineral resources. Through our social, industrial, and agricultural activities, we are changing the composition of the atmosphere, with potentially serious effects on climate and on terrestrial and marine ecosystems. The human population is expanding into less habitable parts of the world, which increases vulnerability to natural hazards and strains the biological and geological systems that sustain life.

If present trends continue, the integrity of the more fragile systems on which human societies are built cannot be assured. The time scale for the breakdown of these systems may be decades or it may be centuries, but we cannot continue to use the planet as we have been using it. Present trends need not continue, because we are unique among the influences that affect earth systems: we have the ability to decide among various courses, to weigh the pros and cons of alternative actions, and to behave accordingly.

The history of the geological sciences offers many reasons to be optimistic. One of the triumphs of twentieth-century science and technology has been the worldwide identification and extraction of energy and mineral resources, an activity that has brought an increased standard of living to an expanding human population. The geological sciences have demonstrated ways of maintaining water quantity and quality, disposing of wastes safely, and securing human structures and facilities against natural hazards. Essentially, the geological sciences teach us about the nature of the Earth and about our role on it.

Suggested Citation:"1 Global Overview." National Research Council. 1993. Solid-Earth Sciences and Society. Washington, DC: The National Academies Press. doi: 10.17226/1990.
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Understanding the Earth

The process of understanding the Earth has just begun. If human beings are to survive and prosper for more than a moment in geological time, an understanding of the intricacies of interacting earth systems is a necessity. We must find and develop the resources needed to sustain and improve the human condition. We must also preserve and improve the environment on which essential and aesthetic human needs depend. We need to know enough to predict the beneficial and destructive consequences of our actions.

Among the questions now confronting solid-earth scientists are the following: How did the Earth form, and what accounts for the composition of its various components? How does the core interact with the mantle, and how does the mantle drive plate tectonics? How have the continents evolved? How has the solid-earth influenced the course of biological evolution and extinctions, and how have these processes affected the Earth? How have the ocean and atmosphere changed over time, and how can they be expected to change in the future as human influence increases? How can wastes be safely isolated in geological repositories? How are the small-scale movements of the surface related to tectonic processes? None of these questions can be answered without contributions from several subdisciplines of the solid-earth sciences. Thus, interdisciplinary interactions will continue to grow in importance as the earth sciences advance.

Because its concerns are with global features and phenomena, the earth sciences are intrinsically an international undertaking. Basic field data must be gathered from diverse regions of the Earth, and earth scientists must conduct experiments on a global basis to accurately determine its composition and dynamics. International cooperation and exchange among scientists in different countries are essential.

Quantitative models have been developed for a number of earth processes. For instance, numerical computer simulations have been devised for mantle convection, for the evolution of sedimentary basins, for surface processes such as erosion, for fluid flow, and for rupture processes in earthquakes. At the same time, solid-earth scientists are relying on increasingly sophisticated instrumentation to expand and to keep up with the data needed for future discoveries and for models that assess and predict earth processes. Even such traditionally descriptive subdisciplines as mapping and paleontology are becoming increasingly quantitative with the advent of digital analyses and computerized data bases.

Predicting the Earth's Future

Better understanding of the way natural processes operate over time, whether quantitative or descriptive, leads to more accurate prediction of the future effects of those processes. For instance, a greater understanding of surface processes enhances the ability to predict such events as floods, landslides, and subsidence, which assault human structures and facilities. This enhanced ability is the basis for land-use planning, enabling society

Suggested Citation:"1 Global Overview." National Research Council. 1993. Solid-Earth Sciences and Society. Washington, DC: The National Academies Press. doi: 10.17226/1990.
×

to minimize the costs and problems associated with geological hazards. The potential losses due to earthquakes and volcanic eruptions have stimulated research on the condition of and changes in the state of the crust before such events, in the hope that similar changes may be used for future predictions.

Prediction in the earth sciences requires an understanding of the role that past events have had in shaping our planet and an accurate projection of data-based interpretations into the future. Field work will remain the principal source of ground truth observations, while laboratory work will calibrate those observations. At the same time, theory will produce generalizations that can be extrapolated to unexplored regions, to different scales, and to events occurring at different times.

Greater predictive abilities should enable earth scientists to tell how human influences will shape the future. Earth systems undergo natural fluctuations on which the changes caused by human influences are superimposed. Distinguishing between natural fluctuations and human-induced changes in earth systems remains an essential task.

An important question is to what extent geological changes, whether driven by natural processes or human intervention, exhibit chaotic behavior. If chaos dominates, the ability to predict many earth phenomena may be limited. But even chaotic systems are subject to statistical predictions related to the size of the events that may be expected and to their average frequency.

THE EARTH AND ITS COMPONENTS

Development of the geological sciences has been marked by two seemingly contradictory but in fact complementary trends. Earth scientists have become ever more aware of the great complexity of the Earth and its constituents; certain individual minerals, for example, are among the most complex inorganic substances known. At the same time, earth scientists are uncovering the principles that lie behind the Earth's bewildering diversity—unifying concepts that bring coherence to a welter of seemingly unrelated observations.

One way to approach the planet's apparent complexity is to look upon the Earth as a system of interacting components. Viewed in its entirety, the earth system is driven by energy from two sources: (1) inside the Earth from primordial energy remaining from accretion and by radioactive decay of elements and (2) from the Sun (Figure 1.1). As it moves through a homogeneous system, energy tends to reorganize that system into components and then to drive physical and chemical interactions among the components. In this way the Earth has been organized into a system of interacting components on a variety of spatial scales. As with any classification, the boundaries between these components are not everywhere sharp; for instance, the Earth contains liquids (in the form of magmas,

FIGURE 1.1 Earth system processes are driven by both internal and external (solar) energy. From NASA Earth System Science report (1986).

Suggested Citation:"1 Global Overview." National Research Council. 1993. Solid-Earth Sciences and Society. Washington, DC: The National Academies Press. doi: 10.17226/1990.
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FIGURE 1.2 Characteristic space and time scales of earth system processes. From NASA Earth System Science report (1986).

groundwater, hydrocarbons, and so on) and gases (Figure 1.2).

The Earth can be organized into temporal as well as spatial components. Geologists demonstrated the great antiquity of the Earth in the eighteenth and nineteenth centuries by analyzing the layers, or strata, of rock formed from sedimentary deposits. Since then, geologists have continued to refine and elaborate the geological time scale through increasingly sophisticated dating and stratigraphic techniques.

The atmosphere and oceans mix too rapidly to carry information about times long past except in their bulk compositions. But some of the rocks in the continents have remained virtually unchanged since their formation billions of years ago. Thus, events that took place 3.5-billion-years ago are frozen like a snapshot in the rocks of the oldest parts of continents. Geologists examine these rocks for clues about conditions when the rocks were formed and changes they underwent thereafter. In this way geologists have been able to chart past changes in temperature, sea level, atmospheric and oceanic composition, volcanism, plate tectonics, the evolution of life, the Earth's magnetic field, sedimentation rates, and glaciation (Plate 2). Earth scientists study this record to learn how the components of the Earth behaved and interacted in the past, to understand how they interact now, and to predict how they will interact in the future.

Geology is a science in which time plays an especially crucial role. This dependence on time adds a unique dimension to geological phenomena. Every rock, every mountain, every volcano is the product of a particular circumstance. Similarly, every period of earth history is in some way special because of the ever-changing combinations of variously interacting spatial and temporal components, including the remarkable consequences of evolving life.

A further complicating factor is the broad range of scales over which geological events occur. The spatial components range from individual mineral grains to objects the size of the Earth and larger, as in the case of the magnetic field. The temporal components range from seconds—the duration of an earthquake—to billions of years. Understanding geological processes therefore involves enormous

Suggested Citation:"1 Global Overview." National Research Council. 1993. Solid-Earth Sciences and Society. Washington, DC: The National Academies Press. doi: 10.17226/1990.
×

extrapolations of experimental and theoretical knowledge.

Until recently, the geological sciences dealt with the great complexity of the Earth largely by focusing on specific spatial, temporal, or compositional regimes. Subdisciplines studied phenomena that were largely compartmentalized, and influences from outside the domain of study were greatly simplified or ignored. As a result, the various subdisciplines of the field—geology, geochemistry, geophysics, paleontology, geohydrology, geoengineering—were neatly pigeonholed and had little need or incentive to communicate or work with one another.

During the past 25 years, that fragmentation of the geological sciences has been disappearing under the influence of several momentous developments. The result has been a profound change in the way geoscientists study the Earth.

UNIFYING FORCES IN THE GEOLOGICAL SCIENCES

Many advances have simultaneously contributed to a general unification of the geological sciences, but three in particular stand out: the plate tectonic revolution, the enhanced ability to produce images of both the surface and the interior, and the increasing recognition of humanity as a geological agent.

Plate Tectonics

In the 1960s the geological sciences experienced a conceptual revolution that continues to affect the field today. Traditionally, most geologists analyzed the history of the Earth primarily in terms of vertical movements: mountains emerged from a buckling crust and were eroded, sea levels rose and fell, whole areas of continents were uplifted. But a quarter century ago a series of developments in marine geology and paleomagnetism—the record of the magnetic signals preserved in the rocks—resulted in a radically new picture of the Earth. This new picture acknowledged the essential role of large-scale horizontal movements throughout the Earth's evolution as well as that of vertical movements.

This concept of plate tectonics has endured through two decades of scientific scrutiny and is now regarded as an established fact, a situation nearly unthinkable in 1960. Scientists now know that the crust is composed of about a dozen major (Plate 3) and several minor plates that constantly move and jostle each other in response to movements in the underlying mantle. Where two plates converge, one may override the other, and the leading edge of the lower plate may melt as it reaches greater depths or may produce melting in the overlying mantle. This convergence creates the oceanic trenches and zones of coastal volcanoes seen on the western edge of South America, in the Southwest Pacific, and elsewhere. If neither plate sinks, collision creates a wrinkled mountain belt, such as the Himalaya or the Urals. Where plates merely sideswipe each other, the boundary shears laterally, as happens along California's San Andreas fault. In each type of plate boundary zone, earthquakes occur when the plates bind, build up stress, and suddenly slip free. A plate may break apart; two observable examples are a rift across a volcanic center such as the Red Sea and a rift through the interior of the plate related to stresses on a distant plate boundary, as at Lake Baikal.

The plate tectonic model enables geoscientists to synthesize formerly separate and enigmatic facets of crustal processes. This ongoing synthesis helps explain the distribution and timing of mountain building, igneous activity, earthquakes, sedimentary basins, ore deposits, and other features of both practical and theoretical import. Plate tectonics also establishes a new view of earth history, in which the plates have moved with time, with consequent effects on the hydrosphere, atmosphere, and biosphere.

Plate tectonics relates activity within the Earth that is directly associated with the movements of plates to characteristics and changes of the surface. For example, midplate hotspots, which are responsible for such features as the volcanic activity at Yellowstone Park and the Hawaiian Islands, are caused by plumes of hot material rising from within the mantle, perhaps from as deep as the core-mantle boundary. Plate tectonics also offers a natural framework for geochemical cycles, which involve the transfer of elements among the various envelopes that form the earth system.

The revolutionary theory of plate tectonics is comparable in power and elegance to the Copernican theory of the sixteenth century, to Newton's theory of gravitation in the seventeenth century, to the establishment of atomic theory at the beginning of the nineteenth century, to the theory of evolution in biology later in that century, and to the development of quantum mechanics and relativity in physics in the twentieth century. Plate tectonic theory is the newest of these major advances in human understanding, and as a result many of its implications have yet to be worked out. Fundamen-

Suggested Citation:"1 Global Overview." National Research Council. 1993. Solid-Earth Sciences and Society. Washington, DC: The National Academies Press. doi: 10.17226/1990.
×

tal questions about plate tectonics remain unanswered. The theory is better at explaining the large-scale features of the Earth than the smaller ones. It suggests the locations of some natural resources but not others. And although the source of the energy that drives the plates is assumed to be convection in the mantle, this is still unproven. These questions are fundamentally important, not only for understanding the functioning of the Earth but also for applying the theory to practical problems such as resource exploration or the prediction of natural hazards.

Images of the Earth

Research in the geological sciences is a data-intensive activity. Many advances in the discipline have occurred when new observations became available or when innovative technologies allowed the gathering of new kinds of data. At the same time, recently revised ideas about the Earth have spurred the development of original instruments and techniques specifically designed to test those ideas.

Measurements of the Earth can today be made with unprecedented levels of accuracy and sensitivity. Just a few decades ago, classical wet chemical methods typically allowed the detection of elements in natural materials at a level of about one part per thousand. Today, mass spectrometers, electron microprobes, and particle accelerators detect elements and isotopes at levels of one part per billion or better from sample areas of just a few microns. Such levels of sensitivity have tremendously increased our ability to date earth materials and analyze the changes they have undergone by measuring isotopic and elemental compositions.

The traditional forms of gathering geological data are field observations and the preparation of geological maps, which remain a fundamental enterprise. Maps of the surface and near-surface are critical in locating and assessing fuels, minerals, and other resources; in analyzing environmental conditions and geological hazards; and in reconstructing the geological history of an area. Maps are the basic tools that geologists use in approaching specific problems (Plate 4). The ability to use maps effectively is greatly enhanced by geographic information systems (GIS), a method of analyzing and integrating digital spatial data of diverse geological and geographical nature.

Geologists have also developed methods for producing images of the Earth's interior. Drilling can probe a few kilometers into the crust to produce measurements and samples of material; beyond a dozen or so kilometers, indirect geophysical methods must be used. Seismic waves, generated either by earthquakes or human activity, are the most effective means of producing images of the deep layers. Geophysicists can detect variations in the velocity of reflected and refracted seismic waves from the surface to its core. These variations (Plate 5) are caused by changes in the density of the materials within the Earth. Laboratory measurements of the physical and chemical properties of earth materials supplement seismic images to model the structure, composition, and dynamics of otherwise inaccessible portions of the Earth. In addition, geochemists sample materials that originated in the crust and mantle and develop experiments that test the range of conditions that led to their formation; both produce further hypotheses about the nature of the Earth's interior.

A new source of striking images began to be produced in the 1960s with the launch of the first satellites designed to observe the Earth and return data to ground receivers. Satellite monitoring offers an integrated and efficient method of gathering information on a global basis. Visual images are one form of remote sensing obtained from orbiting platforms, but satellites also monitor the Earth at nonvisible wavelengths, gauge the gravity and magnetic fields, measure the altitude of the land and sea precisely, and perform a number of other data-gathering operations.

Global positioning systems use satellites to measure the location of receivers on the Earth to an accuracy of a few centimeters. This technique has enabled earth scientists to measure the relative velocities of the plates, determine how the velocities change where plates come together, and assess the rigidity of plate interiors. In the future, global positioning systems may be used to measure changes in the ground surface before earthquakes, volcanic eruptions, or other natural hazards occur. These measurements may lead to reliable predictions of potential disasters and timely warnings to endangered populations.

Observations of other planets by interplanetary probes also have shed light on the history and nature of the Earth. The other planets in the solar system bear striking resemblances and notable dissimilarities to the Earth. Our neighbors in the solar system—the Moon, Venus, Mars, and Mercury—are analog of the Earth, frozen in different states of evolution. Investigations of these planets on an integrated global scale have encouraged earth scientists to adopt a similar approach to our own.

Suggested Citation:"1 Global Overview." National Research Council. 1993. Solid-Earth Sciences and Society. Washington, DC: The National Academies Press. doi: 10.17226/1990.
×

Variations in the Earth's Orbit

It was recognized in the nineteenth century that variations in the Earth's orbit would cause changes in incoming solar radiation that could be important in controlling ice ages. Theoreticians first calculated how these variations would interact, and the study of deep-sea sediments has yielded persuasive evidence that the recurring ice ages are indeed closely associated with orbital cycles. The importance of orbital variations in controlling the climatic changes of the past 2-million-years has proved revolutionary. The critical studies of sediments from deep-sea cores were published less than 20 years ago, and since then application of the idea of orbital control has been applied to studies of ice cores and cave deposits. Researchers now have a yardstick to apply to the complicated record of the most recent past, which is helping to make their interpretations more quantitative. Problems being addressed currently include the extent to which evidence of orbital control can be recognized in older parts of the geological record and how orbital variations (which act directly on insolation) have affected not only such variables as sea-surface temperature but also atmospheric trace gas concentrations.

Humankind as a Geological Agent

The geological sciences have traditionally been responsible for finding and maintaining adequate supplies of fuels, minerals, and nonmineral resources at reasonable prices. The continuing ability to meet this demand depends on basic and applied research in the geosciences. But as human endeavors put pressure on the carrying capacity of settled regions, different components of the Earth's systems are affected. This report therefore does not limit its consideration of resources to the traditional meaning of the word.

Groundwater is an essential resource. In parts of the world the supply of groundwater is dwindling because it is being withdrawn from underground aquifers faster than it is being replenished. Accessible and stable places to live are also a resource that human populations are rapidly consuming. Soil erosion is accelerating in many areas around the world; for every pound of food consumed in the world, an average of 7 pounds of soil is lost to erosion. A habitable environment is a resource that pollutants released to the air, water, or solid-earth can compromise. Biological species of the world are also a resource, but human activities have caused extinctions at an accelerating rate. If current trends persist, a large proportion of the species existing today may disappear during the next few decades.

The consequences of human activity are a recent factor needed to understand earth systems. Before the control of fire, the environmental effects of human beings were comparable to those of other species. Then crop cultivation, animal domestication, and the subsequent appearance of urban civilization introduced a new set of forces onto the Earth. Today, human beings are changing basic earth processes in ways they have never been changed before because of the acceleration and concentration of the effects.

Each person in the United States uses an average of 16 metric tons—about 35,000 pounds—of minerals and fossil fuels each year. This amount includes only the use of materials; it does not include the material moved during the construction of homes, parking lots, factories, dams, and so on. On a worldwide basis, the human population uses nearly 50 billion metric tons of material each year. That is more than three times the amount of sediment transported to the sea by all the rivers of the world.

Clearly, humankind has become a geological agent that must be taken into account in considering the workings of the earth system. If future generations are to have resource supplies in the full sense of the word, decisions must be made within a context that considers the Earth as a total entity. The geological sciences offer information that will be invaluable in evaluating trade-offs and in balancing competing demands.

GOALS OF THE EARTH SCIENCES: RESEARCH FRAMEWORK

There are two fundamental reasons for pursuing the earth sciences. One is to learn more about the world where we live, to satisfy a basic human curiosity about our surroundings and our relationship to them. The other is that research in the geosciences can be used to improve the human condition. Geological knowledge is essential for making decisions regarding the use and preservation of resources or the protection of human life and habitats from the effects of natural disasters.

Stated this way, the distinctions between intellectual curiosity and utilitarian concern may appear fairly sharp, but in fact the two categories overlap extensively. Not all scientific studies have immediate applications, but experience shows that few findings in the geosciences remain unapplied for long. Today's theoretical science may very well be tomor-

Suggested Citation:"1 Global Overview." National Research Council. 1993. Solid-Earth Sciences and Society. Washington, DC: The National Academies Press. doi: 10.17226/1990.
×

row's applied science. The process also works in reverse: applied studies, particularly through their effects on technology, make fundamental contributions to research on the nature and history of the planet.

The geological sciences draw on tools and knowledge developed in several other scientific disciplines, especially chemistry, physics, biology, and mathematics. At the same time, geological research has contributed concepts and techniques to these other disciplines. To take just one example, the structural determination of high-temperature superconductors drew heavily on mineralogical principles, and the perovskite structure of these superconductors is similar to the mineral structure of large parts of the mantle.

Because of its data-intensive nature, the earth sciences have been marked by a particularly close relationship between science and technology. As earth scientists have sought to increase their observational powers, they have developed or refined several devices that were then applied in many other fields, such as x-ray diffraction; electron and ion microprobes; and high-temperature, high-pressure equipment. Similarly, work in the geosciences has produced a number of materials that have found applications far beyond their original realm, including Pyrex glass, zeolite catalysts, and synthetic crystals.

In organizing this report, the committee made extensive use of the close links between basic and applied components of the geosciences. In addition to considering research on the Earth and its components, this report considers the field within the context of problems related to society's needs. The basic science appears within these sections to reflect considerations of how it might contribute to more applied problems.

This organization should not be interpreted as an indication of the relative importance of basic and applied research. Research must not be limited to short-term directed investigation. If it were, scientific innovation and serendipitous discovery would seldom occur, and the plethora of intellectual challenges that provide new dimensions for future scientific opportunity would disappear. A balance must be maintained between basic and applied science, so that each symbiotically nourishes the other.

Goal, Objectives, and Research Themes

Recent research and discoveries have made it possible to consider the Earth as a set of interrelated systems. The concept of plate tectonics provides a grand example of the planet as an integrated system, every part functioning to some degree separately but ultimately dependent on all others. New probes of the interior have reinforced the notion of an internal engine that drives geological processes. The Earth operates as a thermodynamic engine that generates flows and stresses and engenders geochemical cycles. The surface topography is roughly determined by internal movement, and its detailed architecture is sculpted by the action of fluids driven by energy from the Sun with the aid of gravity and tides. The near-surface chemistry involves interaction between the oceans, atmosphere, and fluids from the crust and mantle. The sinking of plates at subduction zones, the slow thermal convection of the mantle, and the volcanism associated with hotspots result in an exchange of materials between the surface and deep interior. The multidisciplinary research themes described in this report reflect a new awareness of the many chemical and thermal exchanges characterizing earth systems.

The GOAL OF THE SOLID-EARTH SCIENCES is:

to understand the past, present, and future behavior of the whole earth system. From the environments where life evolves on the surface to the interaction between the crust and its fluid envelopes (atmosphere and hydrosphere), this interest extends through the mantle and the outer core to the inner core. A major challenge is to use this understanding to maintain an environment in which the biosphere and humankind will continue to flourish.

The OBJECTIVES associated with this goal are:

  1. Understand the processes involved in the global earth system, with particular attention to the linkages and interactions between its parts (the geospheres)

  2. Sustain sufficient supplies of natural resources

  3. Mitigate geological hazards

  4. Minimize and adjust to the effects of global and environmental change

The following RESEARCH AREAS were selected for a dual purpose—they provide comprehensive coverage of the whole earth system, and they identify those processes and topics that offer the promise of achieving the scientific goal:

Suggested Citation:"1 Global Overview." National Research Council. 1993. Solid-Earth Sciences and Society. Washington, DC: The National Academies Press. doi: 10.17226/1990.
×

TABLE 1.1 Solid-Earth Science Research Framework

 

Objectives

Research Areas

A. Understand Processes

B. Sustain Sufficient Resources—Water, Minerals, Fuels

C. Mitigate Geological Hazards—Earthquakes, Volcanoes, Landslides

D. Minimize Global and Environmental Change—Assess, Mitigate, Remediate

I. Global Paleoenvironments and Biological Evolution

I-A

I-B

I-C

I-D

II. Global Geochemical and Biogeochemical Cycles

II-A

II-B

II-C

II-D

III. Fluids in and on the Earth

III-A

III-B

III-C

III-D

IV. Crustal Dynamics: Ocean and Continent

IV-A

IV-B

IV-C

IV-D

V. Core and Mantle Dynamics

V-A

V-B

V-C

V-D

Facilities-Equipment-Data Bases

Education: Schools, Universities, Public

  1. Global paleoenvironments and biological evolution

  2. Global geochemical and biogeochemical cycles

  3. Fluids in and on the Earth

  4. Dynamics of the crust (oceanic and continental)

  5. Dynamics of the core and mantle

These research areas all represent major processes in the evolution of the Earth. They address exploration of the unknown, data collection, and theoretical modeling, and they offer the prospect of breakthroughs arising from new techniques, new instruments, and new concepts. They are all multidisciplinary: none is independent of the others. For example, the lithosphere is the rigid outer layer of the Earth, and its dynamic behavior relates to that of the mantle. The crust, an assemblage of rocks with a variety of compositions, is a blanket on top of the lithosphere, and movements of the crust cannot be considered independently of lithospheric dynamics. Geochemical cycles transfer material within and between the several geospheres; a better understanding of connections between major cycles in which the fluid envelopes dominate and those in which the interior characteristics dominate is a conspicuous need. Much of the material transfer in geochemical cycles is accomplished by fluid transport involving either silicate melts or aqueous solutions. Important investigations of biogeochemical cycles consider the interaction between solid-earth and fluid envelopes. A major factor in changing the paleoenvironments that influence biological evolution is plate tectonics, which is associated directly with mantle convection and lithosphere dynamics. Interconnections are legion, and most frontier research topics relate to more than one theme.

Research Framework

The objectives and research areas of the solid-earth sciences form a matrix (Table 1.1) that provides a RESEARCH FRAMEWORK, with the objectives (A-D) placed along the top and the research areas (I-V) defining the side of the matrix. (The numbering of the latter carries no implication for priorities; it merely reflects the progression deeper into the Earth.) The matrix has obvious parallels with Plates 1 and 2 showing versions of the whole earth system: the sketch of the globe with its interior exposed and the block diagram illustrating

Suggested Citation:"1 Global Overview." National Research Council. 1993. Solid-Earth Sciences and Society. Washington, DC: The National Academies Press. doi: 10.17226/1990.
×

the relationships among the various geospheres. This matrix also outlines the organization of the report, as discussed below.

Every one of the research areas I-V not only requires the further understanding (basic science) represented by Objective A but also has applications to one or more of the societal challenges (applied science) represented by Objectives B, C, and D. Research projects with specific applications can be located in boxes I-B to V-D. Facilities, education, and other topics related to the infrastructure of science are shown below the matrix.

Most of the research discussed in this report fits somewhere into the matrix. The matrix displays the broad spectrum of earth sciences in a manner that avoids putting scientific merit into direct competition with societal needs. It also permits consideration of priority recommendations according to various criteria and from differing viewpoints. Priority is in the eyes of the beholder; different agencies have different missions, and they will enter the matrix at different points. However, the continuity between pure and applied science becomes obvious. Many scientific projects can have multiple objectives and themes, and this factor needs to be considered in setting a priority agenda.

Priority Theme Selection

In every scientific field, subdisciplinary committees and workshops have generated long lists (and short lists) of high-priority research programs. The contributors to this report are all too familiar with these efforts. From many possibilities, the committee selected five research areas and four objectives that include the top-priority scientific issues for understanding the solid-Earth, for discovering and managing its resources, and for maintaining its habitability. These constitute the research framework (Table 1.1) that serves to simplify concepts of classification and relationship. Each of the major objectives is most appropriate for particular research areas, but all are relevant to more than one. Indeed, the potential that a research program will contribute to more than one objective or area is one of the criteria to be used in the selection of priorities.

These research areas and objectives consolidate into eight priority themes. (As mentioned earlier, Objective A, comprehensive understanding, is considered to be implicit in the other objectives.) The aims of these priority themes are summarized in Table 1.2.

The selection of these priority themes represents a preliminary stage in prioritization. If funding can be obtained only in increments, the facilities required to implement these themes need not be established in any particular sequence. If sufficient funding were available, simultaneous construction of these facilities would be a wise investment for the nation. However, it is apparent that not all research programs in this array can be fully funded simultaneously.

Despite current limitations on funds, it is most important to provide the type of support that encourages continuing engagement of the best young minds in postdoctoral independent research. One of the strengths of the American research enterprise is the independence granted to researchers who have fresh ideas and are in the prime of their intellectual careers. But it is widely felt that the system is in jeopardy. The problem is variously ascribed to inadequate funding for the sciences, to a surplus of scientists for the available funds, or to the expenditure of too high a proportion of available research funds on megaprojects. (These issues are discussed more fully in Chapter 7.) Whatever the reason, it is clear that priorities must be established.

Predicting the next scientific breakthrough is difficult. The only prediction that is likely to hold true is that all other predictions will be ''scooped" by some unanticipated discovery. And great discoveries may spring from anywhere; this was illustrated when paleomagnetism and magnetic anomalies turned out to be crucial to the recognition and formulation of the theory of plate tectonics. Any serendipitous advance in instrument design or invention may reveal a deeper level of understanding.

Despite the apprehension of some scientists concerning the definition of scientific programs defined by committees, funding agencies must have guidelines. The priority themes outlined above (and detailed in the next section) are consistent with similar topics selected through the past decade by many committees and workshops for their high research promise. Because the topics are broad, additional evaluation of research frontiers and priorities within each theme is required. It is necessary to determine the instrumental resources required for success and to establish a procedure for determining priorities according to the overall funding available. This must involve considerations of timing and of a logical sequence in which facilities and equipment should be made available to optimize applications of developing technologies. Connections between objectives and research areas within the Research Framework may help to guide some redistribution of effort. The detailed review of the priority themes that follows, with consideration of the personnel,

Suggested Citation:"1 Global Overview." National Research Council. 1993. Solid-Earth Sciences and Society. Washington, DC: The National Academies Press. doi: 10.17226/1990.
×

TABLE 1.2 The Objectives and Research Areas Used Throughout the Reporta

Objectives

A.

To Understand the Processes in All Research Areas

 

To understand the origin and evolution of the Earth's crust, mantle, and core and to comprehend the linkages between the solid-earth and its fluid envelopes and the solid-earth and the biosphere. We need to maintain an environment in which the biosphere and humankind can flourish.

B.

To Sustain Sufficient Supplies of Natural Resources

 

To develop dynamic, physical, and chemical methods of determining the locations and extent of nonrenewable resources and of exploiting those resources using environmentally responsible techniques. The question of sustainability, the carrying capacity of the Earth, becomes more significant as the resource requirements grow.

C.

To Mitigate Geological Hazards

 

To determine the nature of geological hazards, including earthquakes, volcanic eruptions, tsunamis, landslides, soil erosion, floods, and materials (e.g., asbestos, radon) and to reduce, control, and mitigate the effects of these hazardous phenomena. It is important to consider risk assessment and levels of acceptable risk.

D.

To Minimize and Adjust to the Effects of Global and Environmental Change

 

To mitigate and remediate the adverse effects produced by global changes of environment and changes resulting from modification of the environment by human beings. These latter changes may necessitate changes in human behavior. In order to predict continued environmental changes and their effects on the Earth's biosphere, we need the historical perspective given by reconstructed past changes.

Research Areas

I.

Global Paleoenvironments and Biological Evolution

 

To develop a record of how the Earth, its atmosphere, its hydrosphere, and its biosphere have evolved on all time scales from the shortest to the longest. Such a record would provide perspective for understanding continuing environmental change and for facilitating resource exploration.

II.

Global Geochemical and Biogeochemical Cycles

 

To determine how and when materials have moved among the geospheres crossing the interfaces between mantle and crust, continent and ocean floor, solid-earth and hydrosphere, solid-earth and atmosphere, and hydrosphere and atmosphere. Interactions between the whole solid-earth system and its fluid envelopes represents a further challenge. Cycling through the biosphere and understanding how that process has changed in time is of special interest.

III.

Fluids in and on the Earth

 

To understand how fluids move within the Earth and on its surface. The fluids include water, hydrocarbons, magmas rising from great depths to volcanic eruptions, and solutions and gases distributed mainly through the crust but also in the mantle.

IV.

Crustal Dynamics: Ocean and Continent

 

To understand the origin and evolution of the Earth's crust and uppermost mantle. The ocean basins, island arcs, continents, and mountain belts are built and modified by physical deformations and mass transfer processes. These tectonic locales commonly host resources introduced by chemical and physical transport.

V.

Core and Mantle Dynamics

 

To provide the basic geophysical, geochemical and geological understanding as to how the internal engine of our planet operates on the grandest scale and to use such data to improve conditions on Earth by predicting and developing theories for global earth systems.

 

a  

Sequence implies no ranking. All of the research areas and Objectives B, C, and D are treated as priority themes; Objective A involves understanding the processes in each of the research areas, and so was not itself designated as a separate priority theme.

facilities, and equipment required to implement the best programs, should lead to appreciation of which research should be expanded first. These matters are taken up again in Chapter 7.

PRIORITY THEMES: RESEARCH AREAS

The priority themes can be related to form together in a continuous story. The Earth operates as a thermal engine, driven by primordial heat from accretion, by the continuing decay of radioactive material dispersed through the interior, and by energy generated by the gravitational accumulation of the inner core from the outer core. The Earth is hot and continuously releases that heat into the cold abyss of space. Cooling is efficiently accomplished by thermal convection within the molten core and the solid mantle, with its volcanic by-products, and out through the crust and atmosphere. The brittle crust is moved and dislocated in association with the internal convective disturbances. The solid surface is a major boundary in this dynamic system at which energy from the Sun is imported to the planet. For this reason, understanding the surface processes that affect humankind—landslides, earthquakes, volcanoes, ocean cycles, and basin development, with their characteristic accumulation of resources—requires knowledge of the whole dynamic earth system and all of its interrelations. Even the deep core affects the surface and is therefore important to so-

Suggested Citation:"1 Global Overview." National Research Council. 1993. Solid-Earth Sciences and Society. Washington, DC: The National Academies Press. doi: 10.17226/1990.
×

FIGURE 1.3 Distribution of laterite (shaded) on land masses and estimated major ocean surface currents about 80 million years ago. Laterite are soils that form under relatively uniform maritime conditions on windward sides of continents within the humid intertropical, or tropical forest, zone. From Climate in Earth History, National Academy Press (1982).

ciety. For example, convection in the molten iron-alloy core produces a magnetic field that protects most organisms from lethal solar radiation, provides a basis for navigation, and occasionally disrupts electromagnetic communication systems.

Priority Theme A-I: Global Paleoenvironments and Biological Evolution

Ongoing programs have reconstructed climatic and oceanographic conditions during ancient intervals that were much different from those of today. These varying conditions range from intervals when the deep-sea was much warmer than at present and its oxygen content was depleted to times when vast ice sheets spread to regions far from the poles. Efforts to piece together the kaleidoscopic movements of the continental lithosphere, from climate change evidence found in the rock record and from mountain-building and ocean-forming processes, are progressing rapidly. Researchers have established the relative positions of most of the larger parts of the continents with respect to each other and with respect to the North and South poles for the past 500-million-years.

This record of moving plates provides a meaningful framework for the study of paleogeography, paleobiology, paleoclimatology, and paleoceanography. This framework has so revolutionized these fields that they are, for all intents and purposes, new and budding disciplines. Paleogeography produces maps that show not only the relative positions of continental masses but also the locations of high mountain ranges and shallow seas. Finer details, gleaned from paleoclimatic evidence, indicate specific environments such as deserts, coal swamps, and glacial ice (Figure 1.3). Paleoenvironmental maps represent beautiful reconstructions from scientific detective work, and they have become important guides in exploring for minerals and energy resources. These reconstructed maps lead explorers to potential sites of valuable concentrations, formed during continental development, of material such as petroleum and phosphates. The discovery of the submarine hydrothermal vents found at oceanic spreading centers and the associated mineral deposits has revolutionized interpretations of the origins of many ancient ore concentrations.

One important endeavor is unraveling the record of past continental movements. Another is constructing circulation models for ancient oceans and atmospheres. Reconstruction of such circulation models may illuminate distinctive transitions from one stable environment to another, as well as the forcing factors responsible for such transitions. New approaches to the study of global geochemical cycles contribute to these reconstructions of large-scale environmental change. Researchers are only beginning to appreciate how much life-supporting oxygen and heat-trapping carbon dioxide have fluctuated.

The Earth's dynamic environments form the backdrop against which the history of life unfolds. The rock record is a vast repository of information documenting natural processes of trial and error. These natural proving grounds can be considered experiments that offer lessons about the relationship between life and environments—lessons that will serve humans well in their attempt to confront global change in the decades ahead. The most important of these lessons will come from understanding the events of the past 2.5-million-years. The record of the most recent climatic lurch—when deglaciation accelerated around 15,000 years ago—lies right at the surface. The evidence is in the landscape, on the ocean floor, and within the top layers of the remnant ice sheets. Pertinent information is garnered from ice and ocean cores, tree rings,

Suggested Citation:"1 Global Overview." National Research Council. 1993. Solid-Earth Sciences and Society. Washington, DC: The National Academies Press. doi: 10.17226/1990.
×

FIGURE 1.4 Oxygen isotope variations of oceanic plankton, which is a surrogate for climatic fluctuations, over the past 700,000 years. The stages are those reflecting glacial conditions. Note the rapid increase over the past 15,000 years reflecting the transition from the most recent glaciation to the present interglacial. From Climate in Earth History, National Academy Press (1982).

fossil pollen, fossil soils, loess deposits, lake varves, relict shorelines, ancient river channels, and flood deposits. These data are used to build and test computer models of global circulation patterns. Detailed analyses of these data and isotope dating combine with field documentation of landscape evolution to promote recognition of geological thresholds that mark profound changes from one climatic state to another.

Sedimentary rocks from more ancient intervals also attest to periods of global warming and consequent environmental change. Many of the most exciting conceptual developments in modern paleontology are based on explanation of rates, trends, and patterns in the evolution, migration, and extinction of species—all of which can be interpreted only in a context of environmental change. The evolutionary process is becoming more intelligible because of advances in the documentation, resolution, and management of fossil data (Plate 7). Mass extinctions, including the catastrophe that destroyed the dinosaurs, are among the many important subjects in the study of environmental change.

Global environmental changes are of three kinds. First are the secular changes, such as biological evolution. Since the first single-celled organism exchanged chemical compounds with its surroundings, and persisted and even thrived through that exchange, biota have affected the environment in myriad ways. The changes caused by recent human endeavor are not unnatural, but the intensity of those changes, the concentrations and rates, can cause problems. Second are the cyclic changes, such as day following night, ocean basins opening and closing, and mountains being built and eroded. Familiarity with cyclic patterns allows earth scientists to interpret repeating sequences observed in the geological record. Tides, seasons, floods, droughts, sea level changes, and glacial ages all leave distinctive patterns indicating cycles (Figure 1.4). Secular and cyclic changes continue together. Thus, despite the recurrence of patterns, nothing returns exactly to its original state. The third kind of change is catastrophic. These abrupt changes have occasionally punctuated the record with highly unusual events such as the extraterrestrial impact that led to the demise of the dinosaurs.

Understanding earth history must be grounded in reliable chronologies of events. In the decades ahead, solid-earth scientists will benefit from new methods of dating ancient materials and events—the exploitation of previously ignored fossil taxa and the application of new isotopic techniques or of chemical signals that record unique global events in the rocks. A few years ago no one would have envisioned recent radiometric triumphs: dating zircon grains billions of years old with a precision of a few million years, or dating coral skeletons nearly two centuries old with a precision of just a few years.

Priority Theme A-II: Global Geochemical and Biogeochemical Cycles

Geochemical cycles—the cyclic movement of chemical elements, nuclides, and compounds through the great reservoirs of the Earth constituted by the biosphere, atmosphere, oceans, sediments, crust, mantle, and core—have received recent attention because of advances in analytical techniques, data-handling, and modeling capabilities. The reservoirs may be very large, on the scale of the whole Earth, sequestering elements for a billion years, or they may be as small as a backyard, exchanging material with the surroundings over a few days. Plate tectonic cycles, which involve exchange of material between the mantle and the crust, operate on a time scale of hundreds of millions to billions of

Suggested Citation:"1 Global Overview." National Research Council. 1993. Solid-Earth Sciences and Society. Washington, DC: The National Academies Press. doi: 10.17226/1990.
×

FIGURE 1.5 Movements of key elements (carbon, nitrogen, sulfur, phosphorus, and others) through the earth system's biogeochemical cycles. From NASA Earth System Science report (1986).

years. Sedimentary cycling through the land, oceans, and atmosphere operates over hundreds of thousands to hundreds of millions of years. Ocean cycles involving the biological transfer of nutrients between deep and shallow-waters extend over decades to millennia. And atmospheric cycles involving input of gases to, and removal from, the atmosphere have a time scale of days to centuries.

Material transport involving the solid-earth, the atmosphere, the hydrosphere, and the biosphere is biogeochemical cycling (Figure 1.5). The principal elements concerned are hydrogen, oxygen, carbon, nitrogen, phosphorus, and sulfur. These nutrient elements are required by organisms and are obtained by them directly from the atmosphere and hydrosphere. The atmosphere and hydrosphere, in turn, obtain carbon, nitrogen, phosphorus, and sulfur from interaction with the solid-earth. Rocks yield these elements by chemical weathering and by exchanges between water and bottom sediments or volcanic rocks in the oceans. To complete the cycle, the organisms themselves give up these elements to the hydrosphere, atmosphere, and solid-earth either as part of their life processes or after death by bacterial decomposition. Rocks affect life, but also life affects rocks. For example, both bacteria and organic constituents can affect chemical weathering and the soft-tissue remains of ancient organisms are sources for coal and oil and gas deposits. The main elements of the global carbon cycle are given in Figure 1.6.

Humanly altered biogeochemical cycles modify the composition of the atmosphere. For example, the addition of carbon dioxide and sulfur-containing gases to the atmosphere by the burning of coal and oil results in greenhouse warming and acid rain. The burning of coal and oil short-circuits a natural geological process, chemical weathering, that normally proceeds slowly. Humans produce in decades what would take nature thousands to millions of years to produce. Another example is the phosphorous cycle. Phosphorus is ultimately derived from rocks by chemical weathering, but it is rapidly cycled within reservoirs such as soils, lakes, and estuaries. These sensitive environments, which support vital biological activity, overdose on concentrations of fertilizers and detergents containing phosphorus. They choke to death when oversupplied with what is normally a limiting nutrient.

These rapid cycles involving the biosphere, hydrosphere, and atmosphere are linked through the crust to slower cycles involving the interior. The slower cycles occur along ocean spreading centers where new material from the interior reacts with

Suggested Citation:"1 Global Overview." National Research Council. 1993. Solid-Earth Sciences and Society. Washington, DC: The National Academies Press. doi: 10.17226/1990.
×

FIGURE 1.6 The main elements of the global carbon cycle. From Climate in Earth History, National Academy Press (1982).

ocean water and in subduction zones where the lithosphere—after interaction with the atmosphere, hydrosphere, and biosphere—sinks back into the interior and releases volatiles. The chemical reactions characterizing these environments circulate and remobilize water, carbon, nitrogen, phosphorus, sulfur, and all of the other elements that are so important in the biosphere.

Isotopic studies continue as essential tools for investigation of global geochemical cycles. Researchers use various stable isotopes, such as those of carbon, oxygen, and sulfur, to assess biogeochemical cycles. Ratios of stable isotopes of carbon and oxygen, for example, provide important chemical tracers. They may provide answers to fascinating problems such as whether diamonds contain organic carbon that has been recycled into the interior.

New techniques using radioactive isotopes date critical events during biogeochemical cycles. Radiogenic isotopes can also be used to quantify the size and mean age of major global reservoirs. The information emerging from these studies suggests a new way to understand earth systems.

The ultimate goal of studies of geochemical cycling is reconstruction of the historical development of the Earth and its environment. Geochemical cycling is a unifying concept that brings together results from studies of various earth features, including mantle evolution, global tectonics, rock-water interaction, paleoclimatology, and organic evolution. Compilation of geological history and study of modern processes and their rates permit mathematical modeling of these cycles. These models provide a means of evaluating the quantitative significance of specific earth processes during selected intervals of the past. Such modeling can provide a basis for making future predictions.

Priority Theme A-III: Fluids in and on the Earth

Fluids dominate the redistribution of mass and energy through the earth system. Their role is prominent in the generation, migration, and eruption of magmas; in the chemical alteration of masses of rock during metamorphism and mountain building; in the mechanical transport of material on the surface; in the formation of ore deposits; and in the migration and entrapment of oil and gas within sedimentary basins. Water is the active agent in many of the mechanical, chemical, and thermal processes operating within the crust and on the surface. An understanding of fluid flow is needed to predict the movement of contaminants in groundwater aquifers. Fluids also play a role in triggering earthquakes and landslides.

Chemical differentiation of the crust, hydrospheres, and atmosphere involves volcanic activity, beginning with partial melting of the mantle and ending with eruption of material at the surface. The chemistry of magmas is controlled not only by the conditions of melting but also by the physics of rock-fluid systems—a realization that has renewed interest in the physics of magmatic processes. Analyses of physical data, and of the requirements for

Suggested Citation:"1 Global Overview." National Research Council. 1993. Solid-Earth Sciences and Society. Washington, DC: The National Academies Press. doi: 10.17226/1990.
×

FIGURE 1.7 Relationships among principal fluid transport rates and their products. Arrows depict directions of energy, mass flow, and feedback effects. From The Role of Fluids in Crustal Processes, National Academy Press (1990).

accumulation, flow, and escape of melts from within a rock matrix, are beginning to produce coherent explanations. In addition to experimental studies of physical properties at high pressures and temperatures, several theoretical developments have clarified the properties of flow through a deformable rock matrix and have defined conditions for fluid migration by percolation, diapirism, or through cracks (Figure 1.7). These investigations have only begun; coupling of the laws that govern fluid dynamics in rocks is truly a frontier.

One of the most remarkable discoveries of recent years was that of the submarine hydrothermal vents at spreading centers, where ocean water is transformed chemically by heat and interaction within the basaltic crust (Plate 6). The emerging hot springs sustain colonies of huge tube worms and other creatures without photosynthesis. Abundant sulfide minerals precipitate from the mineral-saturated flow. These discoveries have affected many hypotheses, including those about the chemical composition of ocean water and the formation of mineral deposits. Estimates show that an amount of water equal to the volume of the whole ocean cycles through the oceanic crust in about 10-million-years.

Tectonic, hydrological, chemical, and biological processes interact at the surface with a complexity that has hampered accurate understanding of the system as a whole. The reactions that occur at these interfaces produce the surface environment. They play critical roles in determining the quality of fresh water supply, the development of soils and the distribution of nutrients within the soils, the integrity of underground waste repositories, the genesis of certain types of ore and hydrocarbon deposits, and the geochemical cycling of elements. Bacterial activity appears to be an essential component in many processes that contribute to the evolution of the environment. This recent realization has led to the preliminary development of biological remedies for water pollution and methods for waste treatment.

Priority Theme A-IV: Crustal Dynamics: Ocean and Continents

The notion of terra firma is deeply ingrained in the human subconscious, and yet testimonials to the Earth's vigorous dynamics litter the landscape. An abundance of diverse landforms and surface environments, from spectacular mountains to desert valleys, from rocky coastlines to verdant tropical islands, demonstrate ongoing adjustments to the planet's surface. These alterations proceed at a tremendous range of rates; some are detectable only with sensitive instruments, some are catastrophic. Processes such as basin subsidence, mountain uplift, and continental drift occur at rates of only centimeters per year or less—slowly enough to sustain the sense of a solid-earth but persistent enough to completely reorganize the surface in a few million years. Other processes are readily perceptible, such as the violent volcanic eruptions of Mount Pinatubo or Mount St. Helens, earthquake ruptures that displace high rock volumes by many meters within minutes, or mud flows and avalanches that can outrace a sprinting human. The disorientation and stark terror experienced by many survivors of strong earthquakes result from the violation of basic instincts when the solid-earth reveals its inner turmoil.

Throughout earth history continents have assembled, broken up, and reassembled from different fragments—repeatedly flooded by the waters of the ocean and bombarded with objects from outer space. These surface reconfigurations are manifesta-

Suggested Citation:"1 Global Overview." National Research Council. 1993. Solid-Earth Sciences and Society. Washington, DC: The National Academies Press. doi: 10.17226/1990.
×

FIGURE 1.8 Approximate distribution of continental areas between the breakup of the supercontinent Pangea (about 180-million-years ago) and the present.

tions of interior processes. All of the deep oceanic areas are underlain by a thin crust formed within the past 200-million-years. The comparatively simple oceanic crust is made of basalt erupted in a submarine environment at magmatic spreading centers. The oceanic crust then migrates toward subduction zones where it eventually plunges back into the mantle. In contrast, the continental crustal areas are more complex; their growth patterns extend over 4-billion-years. Earth scientists agree that for a short period about 250-million-years ago, nearly all the continental material was consolidated into a great landmass, the supercontinent Pangea (Figure 1.8). They are not sure whether similar supercontinents existed before Pangea because the record of continental history deteriorates with increasing age. The superior quality of the most recent record is a major reason why researchers of continental dynamics concentrate on active processes. Perhaps even more important is that active processes—earthquakes, volcanic eruptions, elevation and depression, erosion and sedimentation—can be studied using methods that cannot be used to study processes that no longer operate.

Understanding continental crustal evolution requires explanation of long-term deformation mechanisms. This would assist the development of realistic plans to mitigate future disasters caused by short-term crustal deformation. Geologists, geodesists, and geophysicists are working on problems of the deformation occurring between and within continental plates. Their questions address the geometries and histories of structures at the margins of plates, the relationships between forces in the crust and upper mantle, and the tectonic nature and evolution of the now-stable interiors of the continents.

The processes of plate deformation leave evidence in the rocks. Rocks of mountain chains are commonly metamorphosed—recrystallized into new minerals—by the physical changes experienced during the burial, strain, and heating that occur during mountain building. Experimental petrologists have devised methods to determine the stability fields for minerals and mineral assemblages in terms of pressure and temperature, providing the framework for evaluation of the depths and temperatures reached by rocks during deformation (Figure 1.9). Our understanding of these processes has involved the combined approaches of field and structural geol-

Suggested Citation:"1 Global Overview." National Research Council. 1993. Solid-Earth Sciences and Society. Washington, DC: The National Academies Press. doi: 10.17226/1990.
×

FIGURE 1.9 Temperature-depth plot showing conditions as recorded by coexisting garnet and plagioclase in Kilburne Hole (Arizona) granulites. The aluminum silicate stability fields are shown as reference (K: kyanite; A: andalusite; S: sillimanite). From Continental Tectonics, National Academy Press (1980).

ogy, calibrated by experimental petrology and thermodynamics.

The discoveries in the European Alps, China, and Norway of mineral assemblages stable only at very high pressures confirm that some continental rocks have been recrystallized locally at depths of at least 100 km and temperatures of 800°C or more. Continental material is too buoyant to remain at this depth, and rapid uplift with concomitant erosion must have occurred. These observations present two challenges. The first is to explain how the continental rocks arrived at such depths. The second is more difficult: that is, how did the rocks return to the surface fast enough to escape the further metamorphism that can destroy assemblages formed at depth?

Researchers are using two approaches for introducing the dimension of time into depth-temperature analyses. The first enlists the power of computer modeling to project the behavior of a rock mass subjected to pressure and temperature changes and influenced by myriad variables, including fluid flow. The second examines isotopic geochronology and thermobarometric pressure values available from radial growth patterns of minerals and from their inclusions. These new techniques, which combine mineralogy with geochemistry, yield direct estimates for the rates of geological processes associated with mountain building. The rates of these processes complement the record of mountain erosion found in sedimentary basins. Geochronologists are now capable of dating rocks and land surfaces with a resolution that was not previously possible. They can confidently estimate how long a mountain range has been elevated and how fast it is being eroded away.

It is becoming apparent that the continents cannot be treated as simple rigid blocks. The rheological properties of the crust need to be established by a combination of field observations, laboratory experiments, and measurements of active crustal deformation rates, which can now be made with the aid of satellites. Large rotations occur during continental deformation. Studies of the paleomagnetic records in rocks have indicated rotations of 90° in 20-million-years within belts 200 km wide. Measurements using global positioning systems have confirmed the evidence of rotation during short (several years) observation terms.

Seismic reflection methods, developed for oil exploration (still its predominant use), when used to study the structure of the continents, have enriched our evidence of the processes operating close to the surface. Several remote sensing techniques, particularly seismology, have produced remarkable advances in theory and data analysis, and exploitation of images showing structure through the entire thickness of the crust and into the mantle continually supplies new data and raises new questions.

Over the past decade, researchers have recognized structural styles associated with large-magnitude extension of the crust. Extensional strains in the continental lithosphere appear to be accommodated in the upper crust by areas of normal faulting called detachment systems (Figure 1.10). Detachment systems adjust to the separation of relatively undeformed crustal blocks, with individual faults slicing through the upper 15 km of the crust and having displacements that measure in tens of kilometers. The results of continental extension are broad areas of mid-crustal rocks veneered by regionally subhorizontal detachments. These detachments have accommodated the removal of upper crustal rocks from the region of extension. Such extended domains exist in the Basin and Range Province of the western United States. They are 100 to 200 km wide and are interspersed with relatively unextended crustal blocks. Over the next decade, interdisciplinary study of the lithosphere in regions of extension should produce significant advances in understanding deformational processes in the continental lithosphere.

While geophysicists, geochemists, experimental petrologists, and structural geologists study the processes that build continents, complementary re-

Suggested Citation:"1 Global Overview." National Research Council. 1993. Solid-Earth Sciences and Society. Washington, DC: The National Academies Press. doi: 10.17226/1990.
×

FIGURE 1.10 Interpretation of a seismic reflection line from the eastern Basin and Range over the Sevier Desert basin and House Range showing major low-angle normal faults (e.g., Sevier Desert detachment, SSD). From J. H. McBride, 1991, Tectonics 10, 1065-1083; ©American Geophysical Union).

search investigates the processes that destroy mountain ranges and fill basins. Physical and chemical weathering promotes erosion of uplifted masses. Streams and rivers entrain eroded sediments and carry massive amounts of material into downstream basins. Accumulating basin deposits sink into the crust, while weathered highlands rebound, relieved of the weight. Researchers studying the Mississippi-Missouri River drainage basin and the Mississippi delta find that while the delta continues to sink, the amount of sediment delivered by the river has decreased because of upstream dams (Figure 1.11). In this case, human intervention is disrupting the balance of crustal dynamics.

Priority Theme A-V: Core and Mantle Dynamics

The internal structure of the Earth has been studied in recent years from several very different perspectives: seismic waves generated by both earthquakes and explosions have shown how the structure varies, geochemical analysis of mantle-derived rock reveals variations in the mantle's composition, and meteorites that are fragments of planetary objects supply information about other mantles, similar to Earth's. Analyses of rare gases from the mantle further describe its history. Each investigative approach contributes to the overall body of knowledge about the deep interior (Figure 1.12).

Heterogeneities within the inner core, the mantle, and the crust are revealed through seismic tomography, in which seismic waves projected through the Earth's layers are built into a three-dimensional image. The speed and paths of seismic waves are indicative of physical properties that vary according to differences in composition, temperature, amount of melting, and other factors. The resulting seismograms permit a depiction of the structure and properties along the path of the wave. The three-dimensional images (see Plate 5) constructed from individual seismic records show trends and discontinuities—such as the discontinuity found at 670 km—with remarkable resolution. These seismic tomographic images showing the three-dimensional structure of the mantle are now possible because of advances in seismic instrumentation and the availability of powerful computers capable of handling data from hundreds of thousands of seismograms. Heterogeneities are commonly interpreted as evidence of density changes, which can be correlated approximately to parts of the mantle that sink because of high density and rise because of low density. This is indicative of convection within the mantle (Plate 8). An important question concerns whether the mantle convects in one or two shells between the crust and the core. Solving the convection question is one of the challenges for the 1990s.

Whereas seismic tomography provides a picture of the locations of heterogeneities in the mantle, geochemical analyses of basaltic lavas and other igneous rocks from the mantle provide information about the compositions and histories of the heterogeneous rock masses involved in convection. The heterogeneities are distinct on both small and large-scales, and their development has taken billions of years—perhaps as long as half the Earth's age.

There is a clear chemical distinction between the mantle source rocks that supply lava to mid-oceanic ridges and those that supply oceanic island volcanoes associated with hot-spots, such as Hawaii. Up to five different sources are required to account for the compositions of ocean island basalts. Isotopes and trace elements in the lavas serve as tracers for detecting the recirculation of continental and oceanic sedimentary rocks into the mantle. One provocative question is whether—and if so, how—subducted lithosphere is able to penetrate through the 670-km discontinuity within the mantle.

Suggested Citation:"1 Global Overview." National Research Council. 1993. Solid-Earth Sciences and Society. Washington, DC: The National Academies Press. doi: 10.17226/1990.
×

FIGURE 1.11 Suspended sediment discharge (millions of tons per year) at six stations on the Missouri River and two stations on the Mississippi River showing how the construction of reservoirs reduced downstream sediment loads by about half during the period 1939 and 1982. After R. H. Meade and R. S. Parker, 1985, U.S. Geological Survey Water Supply Paper 2275.

Suggested Citation:"1 Global Overview." National Research Council. 1993. Solid-Earth Sciences and Society. Washington, DC: The National Academies Press. doi: 10.17226/1990.
×

FIGURE 1.12 Core-mantle transition zone features based on geophysical data. A heterogeneous chemical boundary layer is embedded in a thermal boundary layer produced by a large contrast in temperature between the core and mantle. Large-scale mantle circulation transports chemical heterogeneities to the base of the mantle and returns them to shallower depths by entrainment. The dotted line represents the base of the upper mantle. Modified from T. Lay, 1989, EOS: Trans. Am. Geophys. Union 70, 49; © American Geophysical Union.

High-pressure experimental devices, such as large presses, small diamond anvils, and dynamic shock-wave apparatus provide key data on the properties of material from the core and mantle. Until recently, experiments determining the temperatures necessary for mantle melting had reached pressures corresponding to depths of only 100 to 200 km. Improvements now provide detailed melting and other physical property determinations at pressures that correspond to the 670-km seismic discontinuity. Less detailed measurements are now possible at pressures corresponding to depths approaching that of the mantle-core boundary.

As investigations continue to decipher mantle processes, information about the core builds toward a comprehensible picture. The melting curve of iron has been measured in shock-wave apparatus at pressures corresponding to those at the core. These results provide a basis for estimating the temperature at the transition between the molten outer core and the solid inner core. From that estimate, temperature calculations can be extrapolated both outward to the core-mantle boundary and inward to the Earth's center.

Other high-pressure experiments have assessed the compositional and physical state of the molten core. These results, combined with seismic data that reach to the core-mantle boundary region, feed speculation about a relationship between core-mantle interactions and magnetism. Changes in the main magnetic field, known to be generated in the core, remain a major unsolved problem.

PRIORITY THEMES: OBJECTIVES

The broad objective of earth system science is to understand the intricate processes that make this planet what it is: a world balanced among so many interacting factors that the life-supporting outer layer suggests an incredible series of coincidences. Understanding the interacting factors and incredible coincidences is the challenge facing earth system science. The excitement and importance of this challenge are enhanced by the immediate benefits to society to be derived from that understanding. Comprehension of earth system processes applies directly to the specific objectives of maintaining resource supplies; preventing damage caused by geological disasters; and assessing, mitigating, and remediating effects of global environmental change.

Military analysts sometimes claim that superior technology won World War II and has so far prevented World War III. The wars of the twenty-first century may be of a nonmilitary nature. The enemies may be the modern Four Horsemen—overpopulation, disease, environmental degradation, and resource exhaustion. The preemptive strikes of the next decades could originate from the bastions of technology and in the trenches of research. The winning strategy may depend on an integrated understanding of the earth system—its organic and inorganic components and their interactions.

Priority Theme B:Sustaining Resource Supplies

The resources needed in ever-growing quantities to sustain civilization are land, water, energy, and minerals. Resource geologists are seldom concerned with materials and processes active beyond 10 km into the Earth. This is the shallow crust. Further division separates into the top 10 m, where soil develops and surface water saturates; intermediate depths from 10 to 100 m, where groundwater and surface mining dominate; and 100 m to 10,000 m—the domain of petroleum production, deep mining, and deep groundwater. The distinction is arbitrary and the boundaries gradational, but the different problems of determining structure, under-

Suggested Citation:"1 Global Overview." National Research Council. 1993. Solid-Earth Sciences and Society. Washington, DC: The National Academies Press. doi: 10.17226/1990.
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standing processes, and methods of investigation have enough in common to provide a certain unity to each of the three areas. Basin analysis is emerging as a central field within the shallow crust. Characteristics of the sedimentary rocks within a basin can be used to detect groundwater, petroleum, coal, and ore deposits. Distinct sedimentary packages also provide clues about the way fluid movement has cemented or altered parent rocks.

Researchers now use isotopic methods to determine the ages of surfaces and of shallow materials. These dates influence interpretations of landscape development. For example, soils are complex systems supporting interactions among various earth components. They contain water, which typically cycles on seasonal and annual time scales; organic materials, which flourish over decades to centuries; and silicate minerals, which persist for thousands to millions of years. Soils have always been difficult to study because of the temporal ranges involved. During the past decade, the use of cosmogenic nuclides to determine dates for soil material and processes and of analytical methods that can handle the mass of data, has advanced the fruitful dialogue between geologist and agronomist.

The Earth's landscapes consist of nested drainage basins on horizontal scales ranging from that of a freshet network on a hillside to the vast Amazon Basin. Relating these networks and their evolution to the sedimentary basins that receive eroded material remains a major focus of earth science. Geomorphologists hope that improved temporal resolution will distinguish between the evidence of steady basin evolution and that of catastrophic events.

Surface water and groundwater are absolutely vital resources. But pressure from human activities threatens their availability. Areas of necessary research range from modeling water flow and the kinetics of water-rock interaction to determining surface water quality and monitoring groundwater contamination on a national scale. The disciplinary division between solid-earth science and hydrology fades on close inspection of these research areas; both are components of the larger earth system science.

Fossil fuels are abundantly available but sporadically distributed within the crust. Intense exploration over the past century in the conterminous United States has found most of the major oil fields. Production from these fields has reduced the reserves of much of the primary recoverable petroleum. While domestic exploration continues, the main priority involves increasing production from existing fields. Success depends on multidisciplinary efforts to understand reservoir characteristics, especially heterogeneity. New extraction techniques will endeavor to recover petroleum resources more thoroughly and more efficiently.

Outside the conterminous United States, the petroleum industry still focuses on new reserves in undiscovered oil fields. Modern exploration methods use an integrated approach. This approach first establishes the tectonic environments of basin development (Figure 1.13) and then interprets local depositional, structural, and thermal evolution. This research forms a background for studying potential oil and gas generation within the basin, to assessing possible fluid migration and related diagenetic change, and finally to defining the types of traps in which oil and gas should be located.

Coal is abundant in the United States, but exactly how much can be developed is not clear. It presents significant environmental problems in development and use. Both open-pit and underground mines require the removal and disposal of massive amounts of rock. Burning coal that is rich in sulfur contributes to acid rain. And the combustion of coal and other fossil fuels produces carbon dioxide, which can intensify the atmospheric greenhouse effect. Solving the environmental problems of coal use while maintaining its economic viability is a key challenge for the future.

Coal originates with a peat-rich material and passes through lignitic, subbituminous, bituminous, and anthracitic phases. During these phases the fixed carbon content increases and the percentage of volatile material and moisture decreases. Coal is composed of woody and waxy organic material and is likely to generate gas on burial. Recent research has shown that in some environments and at low latitudes coals are more prone to yield oil. The oil- and gas-producing potential of coals is one of the most significant exploration frontiers at present.

Nuclear power plants represent an efficient energy source, relying as they do on concentrated and enriched uranium for fuel, but problems with dangerous by-products inhibit development of the industry. Solving these problems through containment or chemical neutralization remains the primary task in this area. Earth scientists can contribute to this work through investigations of fluid-rock interactions.

Uranium concentrations occur widely in sedimentary basins, and the fluid dynamics and chemical interactions of aqueous fluids in the subsurface play a preeminent role in their formation. Most of the commercial uranium in the United States comes

Suggested Citation:"1 Global Overview." National Research Council. 1993. Solid-Earth Sciences and Society. Washington, DC: The National Academies Press. doi: 10.17226/1990.
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FIGURE 1.13 Stratigraphic cross section across the Great Basin. From Continental Margins, National Academy Press (1979).

from sedimentary deposits in stream channel sandstone deposits of the Colorado plateau, Rocky Mountain intermontane basins, and the Texas coastal plain. These deposits originated as disseminated uranium was taken into solution and transported in oxygenated groundwater. Where the water came in contact with reducing agents such as carbonaceous logs, leaf material, or various sulfides, the uranium precipitated. Anaerobic sulfate-reducing bacteria living on the organic material may intensify the deposition. The chemistry and dynamics of groundwater flow in basins are central to understanding the mechanisms of uranium deposition. Uranium deposits are most commonly strip mined, although subsurface hard-rock mines and in situ subsurface leaching also exist.

During the 1960s and 1970s, theories about the origin of ore deposits were overhauled by the advent of plate tectonics and by the discovery of metalliferous brines in geothermal systems such as the Salton Sea and black smokers at ocean spreading centers (see Plate 6). Nearly every type of mineral deposit can now be explained by known processes, rather than by ore-forming mechanisms of debatable nature. Replenishment of dwindling available metal resources is promised by the ability to describe and model the processes and to predict probable locations. For example, recognition that the chemistry of igneous intrusions is closely related to plate tectonic processes has led to understanding and additional discoveries of porphyry-copper and porphyry-molybdenum ore bodies. Besides plate tectonic reconstructions, modern mineral exploration also integrates the understanding of volcanology, geothermal studies, geochemistry, geophysics, and economic geology in the successful search for ore deposits.

A picture is emerging of the characteristics of fluid flow in sedimentary basins. New hydrologic research in basin analysis focuses on understanding the geological mechanisms controlling basin-scale fluid flow. This research is also applied toward more efficient and successful exploration for energy and mineral resources. The resource requirements of the planet grow as developing nations increase their consumption of mineral resources while at the same time so do the industrialized nations. Despite these increases, imminent resource depletion is unlikely because major conceptual and technological leaps during the past decade have greatly enhanced our capabilities to seek and develop these resources. The challenge of resource sustainability is discussed further in Chapter 4.

Priority Theme C: Preventing Damage from Geological Hazards

Human society is a part of the biosphere, which exists within the zone where the solid-earth interacts with its fluid envelopes. This zone is perched between the two engines of mantle convection and solar energy that drive geological processes. The more dynamic surface manifestations of those processes can destroy parts of the biosphere, including its human inhabitants and their structures. As society has expanded its population and increased its use of resources, the vulnerability of its encounters with

Suggested Citation:"1 Global Overview." National Research Council. 1993. Solid-Earth Sciences and Society. Washington, DC: The National Academies Press. doi: 10.17226/1990.
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dangerously vigorous processes has also increased. The term ''geological hazards" is used for these perfectly normal adjustments, which have been typical of the Earth's surface since long before even ancestral humans arrived on the scene.

Natural events that are considered hazards include instability of the ground supporting human activities, eruption of lava initiated by processes deep within the Earth, and behavior of water in the hydrosphere above and below ground; even potential impacts by asteroids or comets should be considered hazards. Some human activities can also induce hazards. The consequences of resource acquisition, urban growth, and waste disposal accelerate the rates of change in natural processes. This acceleration may gain a momentum in landscape degradation and climate change that cannot be checked.

Classification of a geological event as a hazard indicates a potential danger or risk. The hazard may pose a relatively minor risk that will have a minimal effect, or it may be a potential catastrophe that involves great damage and loss of life. Most geological hazards can be avoided, or at least tempered, by taking a few responsible measures. These include proper land-use planning, appropriate construction practices, building of containment facilities such as dams, stabilization of landslide-prone slopes, and development of effective prediction and public warning systems. Already measures of this kind have reduced human suffering from geological hazards in most parts of the world.

In the United States, research into the disaster potential of areas threatened by earthquake and volcanic eruption has been spurred by such natural events. The seismic activity common to the San Andreas fault zone jolted the nation to awareness with the San Fernando earthquake of 1971 and the Loma Prieta earthquake of 1989; most recently, the 1992 Landers and Big Bear earthquakes amplified this awareness. The eruptions of Mount St. Helens in 1980 and Mount Pinatubo (Philippines) in 1991 brought the dangers of volcanic hazards (Plate 9) to the attention of scientists, politicians, and citizens. But in addition spectacular geological disasters, there are geomorphic hazards. These are the slow progressive landform changes that evolve into hazards involving costly preventive or corrective measures. For example, the slow shift of a meandering river may undermine a bridge's foundation, eventually causing the structure to collapse; or steady deposition within a harbor area can require extensive dredging to maintain safe accessibility for large container vessels.

Recording, processing, and interpreting geological changes in time frames of seconds to weeks (termed realtime geology) is an exciting new approach that promises to help mitigate the effects of natural disasters. Traditionally, solid-earth scientists have concentrated their studies on time frames of millions or billions of years, and yet many processes take place rapidly. For example, to predict—with sufficient time to avert disaster—when an earthquake will happen, when a volcano will erupt, or when a landslide will occur, data on strain accumulation and release must be gathered quickly and continuously, and an analysis of the data must be performed as rapidly as possible. Researchers in real-time seismology hope to construct networks that monitor the direction and strength of the most destructive earthquake waves and warn threatened communities. Those communities could shut down utilities before the shaking begins; fire threats from broken gas pipes and electricity lines could be reduced, and communication links could be preserved to aid recovery efforts. Orderly procedures could be taken to secure nuclear power plants, and centralized computer facilities could take actions to avoid massive disruptions. Successful networks that track and predict tsunami dangers have been in operation for decades.

Priority Theme D: Assessing, Mitigating, and Remediating Effects of Environmental and Global Change

The environment changes progressively as continents drift, ocean basins open and close, climates fluctuate, and ocean currents adjust accordingly. Geological evidence demonstrates that rates of environmental change vary and that some catastrophic events cause abrupt changes. Humans have continually influenced their local environment, as most living things do, but in the past these disturbances have been minor. However, these influences are increasing. Ecological repercussions traditionally control population pressures, in human as well as nonhuman communities. Now humans have become major agents of environmental—and geological—change. Society has reached such density that its effects are concentrated: humans now move and use more solid material each year than is transported from continents to oceans in all of the world's rivers.

Problems are seldom as simple as they appear. In the beginning of the twentieth century, urban planners were delighted at the prospect of a hydrocarbon-powered transportation system dominated by horseless carriages as an escape from the waste

Suggested Citation:"1 Global Overview." National Research Council. 1993. Solid-Earth Sciences and Society. Washington, DC: The National Academies Press. doi: 10.17226/1990.
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FIGURE 1.14 Schematic for possible groundwater contamination from a variety of waste disposal practices. From Groundwater Contamination, National Academy Press (1984).

discharged by thousands and thousands of horses. What would they think of today's smog, waste motor oils, and mountains of used tires and junked autos or of the negative balance of payments due to importation of the oil that literally drives this burdensome waste?

The growing effects of an industrial society on the environment and on geological cycles necessitate close monitoring of human activities (Figure 1.14). This attention will lead to an understanding of cause and effect, so that precisely what perturbs the system can be discovered and factored into future practices. Not only can the material controlled by human society disrupt physical cycles by increasing mass transfer; it can also disrupt chemical cycles. The conventional cycles of biogeochemical processes concentrate elements into living creatures and into ore deposits and other geological features. Now these processes follow new paths of chemical migrations and concentrations, forming compounds deliberately generated by manufacturing and inadvertently generated by the disposal of materials. Many of these concentrated compounds are toxic. Effective remediation of toxic compounds is possible by controlling the biogeochemical environments at disposal sites.

People all over the Earth are moving from less inhabited rural areas to the environs of often overcrowded cities in hopes of a better livelihood. Wastes produced in and around cities further compromise the quality of surrounding regions. At the same time there is a strong economic force demanding urban renewal, or recycling of crowded urban space. Structures for human habitation, transport, or manufacturing are made taller and heavier, and they may be built on old foundations that cannot support the newly designed structure.

Geology is the main interconnecting element between the craft of civil engineering and the intricacies of nature, and, in that capacity, geology is used to accommodate the demands and to reduce the damages of societal growth. Every effort toward improvement of the human condition necessarily results in some effect on the environment. Geological conditions control the maintenance and influence the quality of human life in both developing and developed regions. Geological understanding not only identifies the potential of major natural disasters but it can also warn of activities that could result in minor disasters or in the waste of resources.

The surface is molded by two competing, but usually sluggish, forces. One force levels and smooths the landscape through erosion and deposition, and the other creates topographic relief by uplift. Humans evolved as bystanders in this competition, but increasingly have acquired an instrumental role—destroying forests and plowing fields, enhancing erosion, creating reservoirs that interrupt sediment migration, and generating massive amounts of carbon dioxide that influence global

Suggested Citation:"1 Global Overview." National Research Council. 1993. Solid-Earth Sciences and Society. Washington, DC: The National Academies Press. doi: 10.17226/1990.
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TABLE 1.3 Approximate Percentages of Expenditures Keyed to the Research Framework of the Federal Agencies for Fiscal Year 1990a

Objectives

Research Areas

A. Understand Processes

B. Sustain Sufficient Resources—Water, Minerals, Fuels

C. Mitigate. Geological Hazards—Earthquakes, Volcanoes, Landslides

D Minimize Global and Environmental Change—Assess, Mitigate, Remediate

I. Global Paleoenvironments and Biological Evolution

2

<1

<1

1

II. Global Geochemical and Biogeochemical Cycles

4

20

1

III. Fluids in and on the Earth

2

12

<1

3

IV. Crustal Dynamics: Ocean and Continent

19

22

4

6

V. Core and Mantle Dynamics

4

<1

 

a  

One percent of the total of $1,368 million is about $13 million (see Appendix A).

climate patterns. Predictions of global change based on historical observations consider only a brief period of geological time; the context for understanding how the environment changes as a result of human activities will be provided only thorough analysis and interpretation of the enduring geological record. While geologists traditionally have based their working hypotheses on the idea that the present is the key to the past, scientists investigating possible environmental changes recognize that the past may well be the key to the future.

RESEARCH SUPPORT

While the federal government is the source of the largest part of U.S. research expenditures in the solid-earth sciences, the petroleum and mining industries are significant contributors in certain areas. Future researchers will benefit from examining past allocation trends.

Federal Funding

Total federal funding for solid-earth science activities in fiscal year 1990 was on the order of $1,368 million (see Appendix A). The details (in relation to the Research Framework) of the types of activities that were supported are given in Appendix A, and their estimated relative percentage is shown in Table 1.3. Given the diversity of agencies and accounting methods, there is some uncertainty about what matrix box is most appropriate for some of the research funds, but the broad picture is valid.

Considering the overall distribution of federal support across the Priority Themes in the Research Framework, there do not appear to be significant gaps, which indicates that the existing national research structure is working reasonably well. Many of the priority themes are already well established. New funding for modern equipment, technical support staff, and adequate ongoing operating support is required to sustain important progress on most of the themes.

Industry Support of University Research

The petroleum industry has traditionally supported hydrocarbon research that involves theoretical and, more particularly, applied geology, geophysics, and geochemistry. Likewise, so has the mining industry. It is hard to assign a meaningful dollar cost to all this research. One rough guide might be this: the seismic exploration industry worldwide is expected to rise to about $5 billion by

Suggested Citation:"1 Global Overview." National Research Council. 1993. Solid-Earth Sciences and Society. Washington, DC: The National Academies Press. doi: 10.17226/1990.
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the mid-1990s. If about 1 percent of this sum goes to related earth science research, industry support would be about $50 million. Other estimates indicate that a range of $100 million to $275 million is expended annually on oil and gas research in the United States in both the public and private sectors. Although most of the research is in-house, both mining and petroleum industries historically have supported research projects in university departments and collaborated in research with federal agencies (e.g., Bureau of Mines and Department of Energy).

Mining industry support of university research typically involves funding graduate student work in the field or laboratory, summer or interim employment of students, consulting arrangements with faculty, and direct grants. During the fiscal decline of the mining industry in the early and mid-1980s, this support diminished considerably as companies cut back on research and exploration activities as well as on geoscientific personnel. In recent years a growing proportion of the supported research has been in the area of low-temperature, heavy metal geochemistry—a reflection of concern with waste management. At the same time, support for basic research in ore-forming processes and igneous petrology has declined.

The petroleum industry currently supports university research through granting foundations in the form of doctoral and master's fellowships, direct faculty support, and grants for equipment and laboratories. At the same time, many companies are providing support directly through their research and operating subsidiaries, either through membership in industrial consortia or through direct funding of research by faculty and students. Additional research funding is handled by trade associations, such as the American Petroleum Institute and the American Gas Association. The industry-supported Petroleum Research Fund of the American Chemical Society has played an important role for decades. A wide variety of university programs have been encouraged through these means, ranging from basic research in petrology, paleontology, and sedimentology to technologies for reservoir characterization, enhanced oil recovery, and seismic signal processing. Petroleum industry support of environmental research is growing. Particular emphasis is being placed on the disposal of solid and liquid wastes and on groundwater management.

The main thrust of oil and gas company research is naturally toward the development of technology and science that can be directly applied to exploration for and development of oil and gas. If an application cannot be defined, support for a research project is unlikely to be granted. It should be noted, however, that a surprising number of research programs pursued by industry have led to significant bodies of fundamental knowledge, which in turn have supported societal endeavors quite apart from the search for energy resources.

An early example is the study of sedimentary processes and sedimentation of the past 10,000 years, which led to funding of American Petroleum Institute Project 51 for study of the northwest Gulf of Mexico. This project was a pioneering effort in basin-wide sedimentology and ecology, which set the stage for subsequent work on deltas and shorelines around the world. Since then, comparable studies of sedimentology have moved offshore to investigate the processes of continental slopes and submarine fans. The results of these endeavors, many of which were supported by industry consortia, are applicable to environmental engineering and to national defense considerations.

The use of regional seismic data to unravel the stratigraphic history of basins, which was pioneered by industry, has led to the idea that global sea level change controls patterns of sedimentation within basins. These studies are leading to a critical reassessment of the various controls on the development of continental shelves and slopes, submarine fans, and carbonate platforms. Each of these depositional environments offers a rich source of information about the sedimentary record of the past and about the continental margins of the present.

While the basis for digital analysis and processing of seismic signals originated in the university community, intensive development of the technology has been carried out by the petroleum industry. Many of the techniques are now used in seismology and also in the defense and medical fields. Furthermore, the need for high-speed signal processing spawned the development of array processors, now widely used for computations of many kinds.

The occurrence, nature, and diagenesis of organic materials in sedimentary rocks is another area of science that incubated in the applications laboratories of the petroleum and coal industries. Investigation of the burial and preservation of organic-rich sediments in modern environments such as the Black Sea illuminates episodes in the past when oxygen-depleted waters occurred in isolated basins. Evidence suggests that sometimes oxygen depletion spread widely over shallow shelf seas. No modern analogs exist for the latter conditions, and the study of these events—which gave rise to a large part of

Suggested Citation:"1 Global Overview." National Research Council. 1993. Solid-Earth Sciences and Society. Washington, DC: The National Academies Press. doi: 10.17226/1990.
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the world's oil resources—aids in evaluation of the processes that control oceanic circulation and lead to relatively rapid changes in the makeup of life in the seas.

Bacterial and thermal alteration of buried organic material forms oil, natural gas, and coal. The byproducts include organic acids, which have an important influence on the reactions between rocks and the subsurface brines contained within their pore space. These reactions affect the processes of lithification, by which friable and plastic sediments are converted to rock, and of metalliferous ore formation.

INSTRUMENTATION, COMPUTATIONAL CAPABILITY, AND DATA MANAGEMENT

Facilities and Instruments

Many advances in the earth sciences have followed advances in instrumentation. In every decade since the 1890s some major change in instrumentation, beginning with the earliest seismographs and the discovery of x-rays and radioactivity, has resulted in major repercussions for the earth sciences. Progress in scientific instrumentation has accelerated at a remarkable rate. The instruments in modern laboratories include those that can produce images of materials on the atomic scale, determine crystal structure under immense pressure (Figure 1.15), and chemically analyze the composition of less than one-billionth of a gram of material.

A paradoxical situation has arisen. On the one hand, the earth sciences now depend on many more laboratory scientists than 25 years ago. New instruments yield more kinds of data of greater precision than ever before. And many more questions are posed and answered at greater rates. On the other hand, the necessary instruments are more expensive and they become obsolete more quickly. Practicing scientists tend to see the glass as half empty, concentrating on the competition, expense, and obsolescence, while administrators and funding agencies consider the glass half full, regarding the numerical increases as proof of the discipline's health. The instruments used by laboratory earth scientists seldom cost as much as $1 million, although some essential data can only be acquired using expensive facilities such as accelerators, mass spectrometers, or synchotrons.

FIGURE 1.15 Schematic of a high-pressure diamond anvil; research using similar apparatus have brought many aspects of mineralogy and geophysics together to understand mantle and core properties and dynamics.

Success in obtaining some of the more expensive instruments often comes from collaboration, consortia, matching institutional and state funds, and other varieties of cost sharing. Within and among institutions, a variety of ingenious schemes for sharing operating costs have developed, while efficiency of use is maintained by the continuing support of competent staff—a policy that allows sharing of equipment requiring highly trained operators. A small number of private foundations with an interest in the development of the earth sciences help by supplementing and complementing public funds.

There is a widespread perception that the overall condition and availability of research instrumentation are rapidly deteriorating. One specific reason for this perception is that it is now 20 years since the solid-earth sciences community began to optimize laboratory instrumentation, at the time of the Apollo program.

The most costly instrumentation in the solid-earth sciences, as in all earth system science, is mounted on spacecraft and on ocean-going vessels. The use of manned and unmanned aircraft as instrument platforms plays a relatively small role at present, except for a continuing commitment from the National Aeronautics and Space Administration

Suggested Citation:"1 Global Overview." National Research Council. 1993. Solid-Earth Sciences and Society. Washington, DC: The National Academies Press. doi: 10.17226/1990.
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to develop space instruments by testing on aircraft. This wide global perspective is growing at the same time that internationally cooperative involvement has increased in programs addressing earth science systems.

Most ocean-going research vessels used for solid-earth sciences research are also used for oceanographic and other earth system science research. The Ocean Drilling Program, which costs about $45 million a year (mainly from the National Science Foundation with a little less than half of the funds come from collaborating countries), represents the largest single current operation in the solid-earth sciences. (Its role is discussed in Chapters 2 and 3.) Its unique contributions to an understanding of how the Earth works are clear. The Continental Scientific Drilling Program is smaller than the Ocean Drilling Program but promises to provide complementary information about continental processes.

Solid-earth scientists have diverse interests in measurements involving space. These extend from the three high-precision distance-measuring techniques—very long baseline interferometry (VLBI), satellite laser ranging (SLR), and global positioning systems (GPS)—through altimetry and magnetometry to remote sensing of the land, especially that using high-spatial-resolution methods such as that available from Landsat and the Systeme Pour l'Observation de la Terre (SPOT). The ambitious plans for an Earth Observing System (EOS) lie at the core of the U.S. global change program.

Theoretical models of earth processes will become increasingly important for solving many problems that simply could not be tackled previously. These include problems that are among those of greatest concern to society. Finding the solutions will require the best research data bases, the fastest computers, and highly imaginative people.

Earth scientists have already developed quantitative models for many earth processes. Numerical computer simulations have been devised for mantle convection, the evolution of sedimentary basins, the concentration of oil and gas resources, climate change, and surface processes such as erosion, fluid flow, and rupturing of the crust in earthquakes. These models are tools that have been used to allow scientists to rapidly test hypotheses about earth processes. The necessary answers involve understanding the complex interactions of many processes. This requires the computational power to handle large numbers of calculations and large amounts of data.

The development of high-performance computing and communications is currently one of the Presidential Initiatives in the United States. It may be time to consider whether a dedicated high-speed computational facility for solid-earth scientists is necessary or whether improved access to current and developing facilities would be more helpful. Whatever route is taken, it is clear that many solid-earth problems will make high demands on available computational facilities.

Molecular geochemistry is one of the exciting earth science frontiers opened up by advances in theoretical chemistry, numerical algorithms, and data-handling capabilities. Calculations are based on quantum mechanical equations governing the bonding and energetics of atoms in minerals and fluids. These calculations provide substantial insight into our understanding of mineral composition and structures and aqueous solution behavior under a wide variety of pressure and temperature conditions. The prognosis for future increases in computational power at both the supercomputer level and the workstation level promises to establish these methods as a major requirement for theoretical studies of solid-earth processes.

Data Handling

Science is experiencing a variety of distinct revolutions in data handling. Very large amounts of data can now be generated very quickly, and much of it needs to be archived. Spatial data amenable to geographic information systems (GIS) characterizes the solid-earth sciences. For much of the United States digital data sets are commonly available for such basic information as topography. That level of coverage, however, is uncommon over much of the Earth. Ironically, higher-resolution digitized topographic data are available for Venus than for Earth, partly because Venus has no ocean but also because of the lack of military and political sensitivities. The same may soon be true of Mars.

In general, the digital revolution is making great changes in the way geological data are used. Geological maps for many areas are stored in digital format, and hard copies are generated as needed. The practical problems of cities and counties that require geological and geographical information are being addressed as GIS allows easy integration of diverse spatial relationships.

The World Data Centres, established as an archive for information acquired since the International Geophysical Year, have worked well as custodians and monitors of geophysical data for nearly 30 years. Global change studies, involving a wider

Suggested Citation:"1 Global Overview." National Research Council. 1993. Solid-Earth Sciences and Society. Washington, DC: The National Academies Press. doi: 10.17226/1990.
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range of data gleaned from ecological and sociological sources, will modify the traditional way that these centers operate.

Study of the solid-earth requires careful archiving of and wide access to regional subsurface information such as seismic reflection data, well logs, core samples, and cuttings. At present, these are all handled in different ways, and much of the data are proprietary in nature. Current systems are working well, but increased access will become necessary as societal needs evolve.

Storage of rocks, fossils, and minerals is the responsibility of museums because proper curation depends on the specialized knowledge of properly trained personnel. The rising base costs of museums are forcing managing boards to take a hard look at how useful museums are to the supporting community. For solid-earth scientists, well-run museums are essential. Fossil collection in particular provokes conflicts among scholars, museums, commercial collectors, and others.

As we look at future programs in global change, geological hazards and their reduction, as well as programs using space-based techniques, a recurring central theme is the need to establish effective data management schemes. Essentially all of our programs are data intensive and depend on digital data. Thus, if they are to be successful, management procedures must be established for organizing the digital data chain from capture to analysis and for making those data available.

Rapidly expanding quantities of earth science data, increased awareness within the community of digital methods, improved technology in both hardware and software, and the necessity for multicomponent data-set synthesis will continue to apply pressure for improved efficacy of data management. Digital earth science data should be available at an international level to broaden the research base for all scientists.

EDUCATION AND EMPLOYMENT

There is a national crisis in science education. The problems are magnified for the earth sciences, to which few students are exposed prior to college. College enrollments in science are decreasing while job opportunities expand—in new areas for which few adequate college programs exist. An aging college faculty and a low level of both public and decision-maker awareness about earth science issues compound the problem. The geosciences profession continues to have to cope with the peculiar problem that a significant part of the population of the United States considers the Earth to be no more than a few thousand years old. Many citizens flatly reject biological evolution, particularly as it applies to the human species. This situation is not likely to change, but its consequences recur prominently from time to time. These conditions contrast with the ever-increasing need for knowledge about Earth because of the growing worldwide consequences of human activities. Sensitivity to this educational challenge is spreading throughout the profession, and energetic initiatives are coming from professional societies, teaching faculty, and other groups. These developing initiatives should enhance general appreciation for the earth sciences and improve the educational status of the discipline.

The Earth sciences are taught in fewer than 5 percent of the nation's high schools. There are few qualified earth science teachers for kindergarten through grade 12 because of the paucity of teaching opportunities. Not only is the opportunity missed to excite youngsters about the Earth, and ultimately to attract a number of them to the profession, but the opportunity to generate interest in science in general is wasted. Study of the earth sciences offers the prospect of focusing students' attention on a subject they are familiar with and already have questions about, such as the local landscape. An innovative approach would begin with local field trips, including the study of biology, which ultimately would lead to explanations involving the study of chemistry and physics. This type of program could serve as a general introduction to science in the context of the real world.

A related concern is a general lack of awareness of the earth sciences in societal issues, a situation that aggravates the educational problem. The average citizen has a need for better appreciation of natural phenomena, resources, and environmental-economic concerns to make informed decisions about protection from earthquakes and floods; about maintaining sources of water, minerals, and energy; and about the threats from acid rain, hazardous wastes, and global change.

The education problem is severe in the solid-earth sciences because of fluctuations in the demand for geologists as well as the severely decreased student enrollments. Historically, the domestic petroleum industry has been the greatest single employer of geologists, geophysicists, and geochemists. As a result of the dramatic decline in petroleum prices in the early 1980s, following aggressive hiring by the industry during the 1970s, many geoscientists found themselves without jobs. At the same time, another major earth science employment segment,

Suggested Citation:"1 Global Overview." National Research Council. 1993. Solid-Earth Sciences and Society. Washington, DC: The National Academies Press. doi: 10.17226/1990.
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the mining industry, was in the midst of a long period of depressed commodity prices. So thousands of mineral resource geoscientists also were without jobs. Many individuals in both fields resorted to early retirement, nongeological employment, or marginal industry employment at levels far below their capacities, and their talents were forever lost to science. This represents a waste of scientific resources orders of magnitude greater than the resources lost by an oil spill, yet no newspaper headlines heralded the event. There is no science equivalent of an Environmental Protection Agency or the National Guard to remedy, or even recognize, a disastrous brain drain.

Enrollment in undergraduate geoscience programs plummeted from 28,000 in 1982 to 9,000 in 1988 and is now rising only very slowly. In the early 1980s, while petroleum-related jobs became scarce, environmental legislation addressing waste disposal sites was enacted and strictly enforced, which opened employment opportunities for individuals with appropriate training. Employment projections indicate a sixfold increase in many geoscience areas during the remainder of the century for Superfund hazardous waste sites alone, and there is no question that employment opportunities in the earth sciences are growing. They are shifting from concentration on resource problems toward hydrology, rock-fluid relationships, and associated problems.

Against these brightening prospects, however, where will the replacement faculty and other geoscientists come from in light of the present extraordinarily low enrollments? If the petroleum industry rebounds from its decline, how will its demands further stress the labor pool? Supply and demand have been out of phase for decades in the geosciences.

Women and minorities are not common among earth science professionals. Some estimates place their involvement as less than 5 percent. Surely opportunities exist to make the earth sciences more intriguing and rewarding for this majority, women and minorities, of the North American population.

Universities and colleges might wish to examine their undergraduate curricula in the earth sciences to see whether they adequately train future professionals and whether they provide scientific awareness for the lay citizen. Introductory geology courses, which represent the only exposure that most students have to the earth sciences, should be stimulating and challenging. Comprehensive courses in earth system science, emphasizing interrelationships and feedback processes, as well as the involvement of the biosphere in geochemical processes, would appeal not only to life and earth scientists but also to a wider range of curious students. Professional programs must increase offerings in emerging fields and might consider phasing out less useful requirements. Growth in both employment and research opportunities can be expected in such areas as hydrology, land use, engineering geology, environmental and urban geology, and waste disposal. The interests of earth science and engineering departments converge in these fields, and opportunities to link the two should be explored. Unfortunately, there are few qualified scientists to teach these programs at the graduate level, because those who are qualified are attracted by the higher incomes of the industrial and consulting fields.

The greatest potential for enhancing earth science education lies with the federal agencies that have programmatic and legislated authority to do just that. Over $360 million per year is spent on science and engineering education by the National Science Foundation and the Department of Energy; the U.S. Geological Survey, which works mainly at the precollege level through development of publications and increasing services to teachers. Other federal organizations have expressed an interest in the education process, including the Department of Defense, the National Oceanic and Atmospheric Administration, the National Aeronautics and Space Administration, and the Environmental Protection Agency. These organizations appreciate the pending problems in the availability of earth scientists and the need for more public awareness of science issues. The need is critical now, as the Department of Energy initiates its multidecade cleanup of waste sites throughout the country, with many projects heavily dependent on earth science knowledge.

When there are opportunities to offer expert advice on issues such as hazard mitigation, the sustainability of life, resource exploration and depletion, and waste disposal, the solid-earth sciences community should be ready.

INTERNATIONAL SCOPE

Earth system science is an intrinsically international undertaking. The global character of geological processes translates into a realization that, for example, many tectonic and sedimentary processes are best illustrated outside our national borders; that volcanic and other hazards are shared by all peoples; that environmental degradation does not stop at political boundaries; and that climatic and sea level

Suggested Citation:"1 Global Overview." National Research Council. 1993. Solid-Earth Sciences and Society. Washington, DC: The National Academies Press. doi: 10.17226/1990.
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TABLE 1.4 Organization of the Report

Overall perspective: Chapter 1

Conclusions, priorities, recommendations: Chapter 7

Facilities, Equipment, Data Bases: Chapters 6 and 7 

Education: Schools, Universities, Public: Chapter 6 

Human Resources, Professionals: Chapter 6

Objectives

Research Areas

A. Understand Processes

B. Sustain Sufficient Resources—Water, Minerals, Fuels

C. Mitigate Geological Hazards— Earthquakes, Volcanoes, Landslides

D. Minimize Global and Environmental Change—Assess, Mitigate, Remediate

I. Global Paleoenvironments and Biological Evolution

Chapter 3

Chapter 3

Chapter 4

Chapter 3

Chapter 5

Chapter 3

Chapter 4

Chapter 5

II. Global Geochemical and Biogeochemical Cycles

Chapter 2

Chapter 3

Chapter 2

Chapter 3

Chapter 4

Chapter 3

Chapter 5

Chapter 2

Chapter 3

Chapter 4

Chapter 5

III. Fluids in and on the Earth

Chapter 2

Chapter 3

Chapter 4

Chapter 3

Chapter 4

Chapter 3

Chapter 5

Chapter 3

Chapter 4

Chapter 5

IV. Crustal Dynamics: Ocean and Continent

Chapter 2

 

Chapter 3

Chapter 3

 

Chapter 4

Chapter 2

 

Chapter 5

Chapter 5

V. Core and Mantle Dynamics

Chapter 2

Chapter 3

Chapter 4

Chapter 5

Chapter 5

changes occur all over the world. Basic field data must be gathered from diverse regions of the Earth, and earth scientists must conduct their experiments on a global basis to accurately determine the composition and dynamics of the whole Earth. International cooperation and exchange among geoscientists in different countries are thus essential. The successes of a variety of programs of international scope, such as the Ocean Drilling Program and global seismic networks, attest to their value to the earth sciences.

In 1982 the National Science Board concluded that the United States was at a critical point in its international scientific relationships. The technical lead had been lost in many fields at the very time when the global nature of scientific problems was becoming more apparent. The loss of scientific leadership translates directly into lost technological edge and lost trade advantages, as well as lost science.

Economic and scientific common sense dictates that the interests of the United States in the global economy and in the global scientific community are best served by strong international science programs. Compelling arguments can be presented that in the future U.S. energy and minerals resources will be drawn from overseas to an even greater degree. Because of this dependency, information about the amount and distribution of global resources will be required for a range of policy decisions.

ORGANIZATION OF THE REPORT

The chapters in this report are keyed to the research framework, as can be seen in Table 1.4. Following the definition of goals and objectives and the Global Overview of the priority themes in this chapter, Chapter 2, Understanding Our Active Planet, concentrates on the Earth's internal workings. Research into the relationship between the core and mantle, and the dynamic convective motions within the mantle, has advanced rapidly. New results are bringing researchers closer to understanding how internal processes affect events at the Earth's surface: earthquakes and volcanoes in the

Suggested Citation:"1 Global Overview." National Research Council. 1993. Solid-Earth Sciences and Society. Washington, DC: The National Academies Press. doi: 10.17226/1990.
×

short-term, and plate tectonics and mountain building in the long-term.

Chapter 3, The Global Environment and Its Evolution, is concerned with the crust and its interaction with the fluid envelopes, which is driven by solar energy. Past environmental changes and their effects on life can be determined from the study of sedimentary rocks, which contain the record of ancient environments, including information about the composition of the atmosphere and oceans through time. Studies of continental, oceanic, and atmospheric processes have been revitalized by the integration of this compositional information with interpretations of plate tectonic movement and the resulting changes in distribution of continents and ocean basins. The record of rocks and fossils also documents evolution and extinction and provides an intellectual framework for understanding humanity's place in nature.

Chapter 4, Resources of the Solid-Earth, includes environmental concerns related to resource extraction and use. Groundwater, and the flow and reaction of fluids within the crust, is a pervasive theme associated with most geological resources. The report therefore considers water as well as the traditional earth resources of minerals and fossil fuels.

Chapter 5, Hazards, Land Use, and Environmental Change, addresses the geological problems facing humankind and involves research throughout most of the matrix. Topics include hazards caused by earthquakes, landslides, and volcanic eruptions; environmental changes associated with urban growth, engineering, and agricultural practices; and some modern consequences of the long-term global change reviewed in scientific terms in Chapter 3.

Chapter 6, Ensuring Excellence and the National Well-Being, reviews topics such as education, demographics, instruments and facilities, the revolution in data gathering and handling, and international collaboration.

Chapter 7, Research Priorities and Recommendations, tackles the problem of determining science priorities for the whole array of research activities covered in Chapters 2 through 6 and the sources of federal funding for solid-earth science research. The top-priority and high-priority research selections and the facilities required for their implementation are outlined.

There are two informative short-cut paths between Chapters 1 and 7, highlighted for easy identification. Essays at the beginnings of Chapters 2 through 6 provide the sense of the science in each chapter. At the end of each chapter, the most promising research opportunities are summarized in research frameworks without background detail (these are also collected into a single table in Chapter 7).

Suggested Citation:"1 Global Overview." National Research Council. 1993. Solid-Earth Sciences and Society. Washington, DC: The National Academies Press. doi: 10.17226/1990.
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As environmental problems move upward on the public agenda, our knowledge of the earth's systems and how to sustain the habitability of our world becomes more critical. This volume reports on the state of earth science and outlines a research agenda, with priorities keyed to the real-world challenges facing human society.

The product of four years of development with input from more than 200 earth-science specialists, the volume offers a wealth of historical background and current information on

  • Plate tectonics, volcanism, and other heat-generated earth processes.
  • Evolution of our global environment and of life itself, as revealed in the fossil record.
  • Human exploitation of water, fossil fuels, and minerals.
  • Interaction between human populations and the earth's surface, discussing the role we play in earth's systems and the dangers we face from natural hazards such as earthquakes and landslides.

This volume offers a comprehensive look at how earth science is currently practiced and what should be done to train professionals and adequately equip them to find the answers necessary to manage more effectively the earth's systems.

This well-organized and practical book will be of immediate interest to solid-earth scientists, researchers, and college and high school faculty, as well as policymakers in the environmental arena.

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