Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter.
Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 5
2
Earth Sciences: A Mission to Planet Earth
BACKGROUND
We now have the technology and the incentive to move boldly
forward on a "Mission to Planet Earth. The steering group calls
upon the nation to implement an integrated global program of
fundamental research with space-borne and earth-based instru-
mentation. Such a program would probe the origin, evolution,
and nature of our planet, its place In our solar system, and its
interaction with living things, including mankind.
For earth sciences it is particularly appropriate to focus on
planning for the period from 1995 to 2015. This is because the sci-
ence base of this discipline is well developed. Various observational
systems have already been established, and programs extending
into the last decade of this century have already been proposed.
The long lead times associated with the development of space-
craft and sensors mean that recommendations adopted now will
not affect current programs until at least the ~rnd-1990s. Thus, a
planning document at this time Is particularly relevant.
During the past 2 or 3 years, there has been an enormous
amount of planning for a study of Earth as a global system, and
for an observing system to monitor global change. It is clear
5
OCR for page 6
6
that such a system must be largely space-based, yet the earth-
based part of the measurements Is integral as weD. Several recent
reports have helped to set the scientific context for such global
studies. These have come from the National Research Council
(Committee on Earth Sciences, Committee for the International
Geospher+Biosphere Program, Space Applications Board), from
NASA (Cobb Habitability, Earth Systems Sciences Committees,
and Tom the International Council of Scientific Unions (Com-
mittee on Global Change). The technological context in which
these studies will be carried out will depend largely on the pace
of development of global observing systems. (For a general policy
statement on cooperation, see Chapter 10.)
EARTH AS A GLOBAL SYSTEM
The records of the first human attempts to understand Earth
are lost in antiquity, but we know that early man made exploration
voyages ~ the Pacific, Atlantic, and Indian oceans. As early as
the third century B.C. the Greeks knew that Earth was a finite
globe and were able to est~rnate its circumference. Thus, from
ancient times to the present, we have used exploration and physical
reasoning to understand earth processes and to explore the Earth's
place in the solar system.
Modern techniques and new integrated programs have yielded
improved information about the state of the atmosphere, the
ocean, and the Isnd surface. We have been able to directly measure
continental drift, and to probe Earth's crust by drilling; seismic
and acoustic techniques have let us probe even deeper. In addition,
we now possess improved weather forecasts and new information
about agricultural conditions. Measurements of winds and waves
on the ocean's surface, of ocean currents, of primary productivity
in the ocean, Ad of the chemical constitution of the atmosphere
have all added to our understanding of global systems.
Very recently, interest has focused on problems where ad-
vances could have unport ant societal impacts. These problems
include the prediction of earthquakes, volcanoes, and climatic
anomalies such as E! Gino, whose economic impact is measured
in billions of dollars. The increase in the atmosphere of carbon
dioxide and other gases that may contribute to a "greenhouses
effect has also focused attention among scientists. New tools and
ideas wait allow us to address such problems.
OCR for page 7
7
We also have much new Formation about the atmosphere
and surface properties of the other planets that will help us in
understanding our own. As we have learned about the other
planets of the solar system, it has become evident that Earth
is different ~ several remarkable ways. The blue and white of
Earth contrast sharply with the red of dusty Mars, the dazzling
whiteness of Venus, and the complex swearing colors of Jupiter.
Continued exploration has shown other, fundamental differences
between planet Earth and Al other planets of the solar system.
The most striking of these is that living creatures have existed
on Earth for more than 3.5 billion years, evolving continuously
from the supplest one-celled organism to the present diversity of
life forms. In contrast, it is probable that biological activity is
not and perhaps never was—present on any of the other planets
during the lifetime of the solar system.
Because liquid water is essential for life on Earth, the sur-
viva] and evolution of biological organ~srns provide a convincing
argument that Earth has always had water on its surface at a
temperature to keep it liquid. Without the oceans, Earth's at-
mosphere would be profoundly different. For instance, we have
Only modest amounts of carbon dioxide in our atmosphere, thus
avoiding the greenhouse effect experienced by Venus. It is believed
that nearly all the carbon dioxide that has Bowed from Earth's in-
terior has been buried In ocean sediments as I~rnestone or organic
carbon. The presence of free oxygen would be impossible without
the photodissociation of water ant] the consequent escape of hy-
drogen. Without the presence of oxygen, ozone would not exist in
the stratosphere to shield surface life from destructive solar radi-
ation. Most animus could not then exist, since they depend on
oxygen-based metabolism.
In turn, other processes must limit these ocean effects to keep
Earth habitable. Oxygen ~ moderate amounts is a necessity for
animal life, but in higher concentrations it is toxic. If organic nu-
trients continued to accumulate In sediments, all nutrients would
eventually return to insoluble forms. If limestone sediments con-
t~ued to accumulate without a compensating inflow of carbon
dioxide, photosynthesis would taper off as the carbon dioxide con-
centration fell.
Such a compensating inflow of carbon dioxide does, in fact,
occur as part of the remarkable phenomenon of plate tectonics.
This process of continual recycling of Earth's surface materials
OCR for page 8
8
into the interior, and their reappearance In mid-ocean ridges and
volcanoes, is probably essential to preserving Earth's benign en-
vironment. Moreover, motions deep ~ Earth's interior drive the
plates and generate the magnetic field that partially shields it from
the harsh environment of space.
Thus it is Earth's own inner life, together with the interactions
of its unique surface phenomena, that has determined its history
and our own. A convective process deep In Earth's core fired
by radioactive decay and the primordial heat of agglomeration
has joined the complex interplay of the atmosphere and oceans
with the biosphere to forge the world we know. However, major
questions remain unanswered. Why does the phenomenon of plate
tectonics operate on Earth but not on Mars and not, perhaps,
on Venus? What are the characteristics of Earth that make plate
tectonic convection possible? What are the nature and rate of
convection? What are the ejects of changing rates of convection on
atmospheric carbon dioxide concentration, and hence on climate
and on the biosphere? What insights can we gaper from studies of
the variable magnetic field generated by Earth's interior dynamo?
How do the ocean and the atmosphere interact to produce Tong-
term climate change? What is the role of the biosphere In climate?
And, finally, how does Earth work as a system?
Even the origins of life may be related to plate tectonics.
We have discovered complex ecosystems around deep-sea vents in
the mid-oceaa ridges. In the vents' scalding water live anaerobic
sulfide-oxidiz~ng bacteria that provide the energy and organic com-
pounds for the local animal inhabitants. This environment may
have been the cradle of life on Earth, despite its inaccessibility
to photosynthesis. High temperatures would have Plowed rapid
chemical reactions and reduced sulfur compounds for energy. The
overlying water would have shielded organisms from destructive
ultraviolet radiation.
Another unanswered question Is the eject on Earth of asteroid
and comet collisions. What has been their effect on the evolution
of life? The "great dyings~ in the biological record may be due to
these collisions, stimulating, in turn, the rapid evolution of new
life forms. A careful search for evidence of such collisions in the
geologic record could throw a new light on evolutionary processes.
In more general terms, it is clear that a comprehensive study,
from Earth's outer atmosphere to its inmost core, is essential to
understanding the conditions for life. Advances in our ability to
OCR for page 9
9
observe the planet both from space and from Earth itself now
make such a global study possible. For example, we will soon
possess computers that can mode! the turbulent flows typical of the
oceans, the atmosphere, and molten materials. Between now and
1995 many of these earth-monitor~ng systems will be tested, and
a number of research missions for remote sensing will be carried
out. As the steering group looks to the period 1995 to 2015, it
foresees the application of these results to the development of an
ongoing observational system for the Earth. Understanding Earth
as a complex whole will begin from such global studies.
SCIENTIFIC THl:MlDS
Four overarching scientific themes (also cawed regrind themes"
will guide the study of earth processes:
1. Determining the composition, structure, and dyna~nics of
the Earth's interior and crust, and its evolution.
2. Establishing and understanding the structure, dyna~rucs,
and chemistry of the atmosphere, oceans, and cryosphere, and
their interactions with the solid earth.
3. Characterizing the interactions of living organisms with the
physical environment.
4. Understanding and monitoring the interaction of human
activities with the natural environment.
The first of these themes is aimed at determm~g the compo-
sition, structure, and dynamics of Earth's interior and crust, and
understanding the processes by which Earth evolved to its present
state. Important properties of the mantle such as its composi-
tion, the spectrum of convective scales, and the relation between
roicanism and tectonics ace not understood. We will require mea-
surements by seismic and other arrays of earth-based instruments,
together with computer modeling and the monitoring of global
gravity and magnetic fields, to fathom these processes.
The second theme is aimed at understanding the structure,
dynamics, and chemistry of the oceans, the atmosphere, and the
cryosphere. The interaction of these with the solid earth must
then be detailed. Today we do not understand the factors that
determine the global circulation of atmosphere and ocean, and
the interaction of the atmosphere with surface geological and hy-
drological processes. The effects of biological processes on the
OCR for page 10
10
hydrological cycle, climate dynamics, and geochemistry are ma-
jor problems. We require satellite measurements, calibrated and
validated from the ground, of these global-scale processes. For ex-
ample, there is a pressing need for an instrument in orbit that can
measure the rate of precipitation on the Earth—a major element
in all models of the earth system.
The third theme deals with characterizing the interactions of
living organisms among themselves and with the physical environ-
ment. This includes their effects on the composition, dynamics,
and evolution of the ocean, atmosphere, and crust. The biosphere,
for instance, controls the oxygen content and other aspects of the
atmosphere, the oceans, and the solid earth. Yet land and ocean
ecosystems are poorly understood or described today. Global mea-
surements of biota from space, coupled closely with field exper-
iments, are the key to better understanding ~ this realm. For
example, ocean chIorophyD could be quantified by combining color
measurements of the ocean with surface observations.
The fourth theme addresses human interaction with the natu-
ral environment. Human activity clearly affects the concentration
of gases like carbon dioxide and methane in the atmosphere, as
weD as the amount of dust. Population increases and deforestation
have uncertain implications for cInnate and genetic diversity. Con-
versely, many developments have made mankind more vulnerable
to natural hazards. Some of these phenomena are best monitored
from space, provided that proper calibration and validation are
available.
RECOMMENDED PROGRAM: POST-1995
It is clear that to observe such ~ mteractire add complex
system as Earth we need both satellite and surface measurements.
Satellites provide the global context for regional field studies, and
most often are the only way to acquire global data. In particular,
the steering group looks to a set of geostationary satellites to
provide rapid synoptic images of the whole Earth. In addition,
polar orbiters would provide high-resolution data and fill in the
polar gaps. Special-purpose orbiters at various inclinations and
altitudes would provide measurements as needed and communicate
with instrumentation on the surface and in the atmosphere. A key
requirement of these observations is their global completeness and
OCR for page 11
11
simultaneity. Also, the observing system must be designed to
assure continuous and consistent measurement over decades.
The volume of data collected by this many-faceted observing
system will require faster, more automated, and more adaptable
processing systems. Consistent formatting of different types of
data Tom the atmosphere, oceans, and land will be essential.
Better integration of modeling and observations will be another
important aspect of future earth science systems. It is essential
that data acquired over the globe be used both as inputs to these
models and as tests for mode] predictions. This accomplished,
scientists could use the entire Earth as a laboratory, following
earth processes through their evolution. As always, advances in
understanding require a mixture of empirical and fundamental
approaches.
Specific recommendations given here, when implemented, will
build on the results expected Tom the sensors and platforms of
the NASA Earth Observing System (EOS), currently scheduled
to fly as part of the Space Station complex in the m~-1990s.
EOS, ~ turn, wiD build on its predecessor missions: the Upper
Atmosphere Research Mission, the Navy's Remote Ocean Sensing
System, the Ocean Topography Experiment, the Geopotential Re-
search Mission, the Tropical Rainfall Mission, and the Magnetic
Field Explorer. Other nations' missions, such as the European
Space Agency's ERIC and Japan's Marine Observation Satellite
1, wait also help define the specific parameters needed for adequate
earth monitoring. EOS wit be the next phase in the development
of long-term measurement systems. But here the steering group
looks beyond the initial deployment of EOS to lay out a series of
specific recommendations for structure and programmatic content
of a long-term mapping and monitoring system for Earth.
~ this time period (1995 to 2015), the steering group suggests
the following elements of an internationally sponsored program
(U.S. responsibilities medicated):
I. A Satellite-Based Observing System
a. A set of five geostationary satellites ftwo provided by the
United States) designed to carry a wide variety of instruments to
cover the entire Earth for long-term measurements (replacement
as required).
b. A set of two to six polar-orbiting platforms (two to three
promded by the Unfed States) to cover the polar areas above 60°
OCR for page 12
12
and to provide platforms for instruments that must be closer to
Earth.
c. A series of special missions that require other orbits.
Examples range from Shuttle-based instrument tests, to Explorer-
type missions, to the Global Positioning System array of 18 satel-
lites. With growing international interest In remote sensing of the
Earth, the steering group expects an increasing proportion of joint
or non-U.S. missions.
2. A Complementary Earth-Based Observing System
The steering group recommends the continuing development
and deployment of a system of earth-based measuring devices to
provide complementary data to the space-based observing networic.
The data from the network should be transmitted in read time
and integrated with observations from space. This earth-based
system is an essential element of any observing system for Earth;
it measures effects that cannot be detected through remote sensing
from space, providingincreased resolution in regional studies, as
wed as calibrating and validating space observations.
3. Theoretical Modeling
State-of-the-art computing technology must toe utilized for data
analysis and theoretical modeling of earth processes. Modeling
earth systems wait require the best data sets possible, the fastest
computers, and ~rnaginative ideas from research. In turn, modeling
can set the context and give direction to future observations.
4. Data Systems
A coordinated system for both archiving and disseminating
earth-related data must be established. This is a call not for a central
archive, but for a central authority or data management unit.
This authority would establish formats and other conventions,
identify data location, and provide easy access to all data as
required. The data rates from the earth-observing system will be
high, on the order of t0~4 to 10~5 bits per day. This ~~l require
much selective averaging and heavy use of new data storage and
retrieval technologies. Automation of some phases of the selection
and averaging process will be required.
TlIE }tO[E OF NASA IN EARTH SCIENCES
The National Aeronautics and Space Administration is to be
commended for the strong role it has played to date in earth
sciences. Its efforts have ranged from studies of atmospheric,
OCR for page 13
13
oceanic, add land surface processes to studies ~ the field of the
solid earth sciences. For a long time, satellites have been used
not only to sense properties of the atmosphere, ocean, and land
surface, but also to define more precisely the shape of the Earth
and to investigate the distribution of mass in its interior. As the
new Earth Observing System (EOS) is developed, NASA should
continue to play this key role ~ the development not only of space-
based technology, but of the necessary earth-based systems and
data systems as wed.
The steering group endorses the position of the Earth ON
serving System Science and Mission Working Group that in future
NASA missions ~sateDit~obtamed data must be used in concert
with data from more conventional techniques. The steering group
agrees that, in addressing multidiscipInnary problems, "observa-
tional capabilities must be employed which range in scale from
detailed ea~th-based and laboratory measurements to the global
perspective offered by satellite remote sensing." Clearly, such
studies must be carried out together with the other agencies that
support basic research in earth sciences, notably NSF, USGS, and
NOAA, as discussed below. But a strong program withm NASA
itself must be mmota~ned.
In particular, the steering group notes the importance of a
strong program In the solid earth sciences. NASA could play a
major role in a comprehensive program that deals with all of the
most exciting and important questions in that discipline today.
These questions include the origin of magmas, the driving forces
for plate tectonics, add the generation of Earth's atmosphere.
Moreover, high-resolution mapping of Earth's gravity field ~ em
sential if ocean surface topography measurements are to reach
their fuh potential for ocean circulation studies. NASA's eng~-
neering capability in stat~of-the-=t technology (e.g., advanced
satellite systems ~d data base management) is essential to the
accomplishment of these objectives.
NATIONAL COORDINATION
Communication among the heads of the Office of Science and
Technology Policy, the Office of Management and Budget, and
the federal agencies involved in the civilian earth science effort is
needed to develop coordinated progrmns and budgets. This re-
quires fuD cooperation among the agencies involved: NASA, NSF,
OCR for page 14
14
NOAA, USGS, DOE, and others. The roles of these agencies rela-
tive to one another NASA as a research and development agency,
NSF as a supporter of basic research, and NOAA and USGS as
operational, m~ssion-oriented agencies In earth sciences provide
a test case for such cooperation. The steering group recognizes
the unportance of establ~sh~g clear roles, especially as researchers
look to measurements on longer and longer time scales.
Coordination with the commercial sector Is also essential.
Plans are under way to operate the Landsat sensor package com-
mercially, and the trench are already flying a similar set of instru-
mentation on their Systeme Probatoire d'Observation de la Terre
(SPOT) satellite series. The data are available com~nercially. ON
portunities to fly other sensor packages, such as meteorological
sensors, on leased spacecraft may occur in the future. Thus, any
comprehensive program must include the commercial sector as a
major player.
CONCLUSIONS
We now have the technology and the incentive to mount a
Mission to Planet Earth." The United States should implement
this integrated program of fundamental research on the origin,
evolution, and nature of our planet, its place in our solar system,
and its interaction with mankind. The m~ssion's feasibility has
been demonstrated. We now need to act.
In order to mount this mission we need to deploy a major
observational system with arrays of satellites and earth-based in-
strumentation for long-term measurements. In addition, we must
bring into play new supercomputers, establish comprehensive data
systems, and fund scientists, engineers, and other participants
who make the program possible. This broad program will re-
quire support from many federal agencies, private industry, and
the international community. NASA will play a key role in the
implementation of the program.
Representative terms from entire chapter:
solid earth
