for example, links to life and biological evolution (Area I) and has influenced paleoatmospheres and paleoceans theme (Area I), as well as playing a major role in continental weathering theme (Area III). It also has connections to the mantle through the igneous and metamorphic processes in the lithosphere and crust (Area IV), as discussed in Chapter 2. Some of the many applications of these Research Areas are outlined in Chapters 4 and 5.
If extended to soils, the new age-determination capabilities that are being applied to landforms and drainage basins could quantify temporal aspects of soil development that have been the subject of much speculation. More complete understanding of soil processes as aspects of environmental, especially climatic, evolution will improve both paleosoil and soil-contamination studies.
Given the important role of glaciers in controlling sea level and climate, and considering the evident instability of glacial volume, it is essential that we gain a clearer picture of the history of glaciation since the onset of the recent ice age about 2.5-million-years ago. Especially important too is further study of the annual layers in ice cores, including analysis of oxygen isotopes, carbon dioxide, and dust to obtain a record of the past few thousand years. We need a much better understanding of glacial expansion and contraction and the role of environmental thresholds in governing these processes.
The record of change in the Quaternary (the past 1.6-million-years) is important because it is the most complete available record for any part of the past and thus provides the best picture of environmental change. Synthetic and snyoptic studies of Quaternary history (e.g., CLIMAP and COHMAP) have led the way. Extending studies of this kind with better spatially distributed data and higher temporal resolution will help to show how phenomena occurring simultaneously in different areas were related to each other, and will indicate sequences of events. This kind of information is needed to test atmospheric and oceanic models that are being used to assess what might happen in future global environments.
The evolution of the ocean, atmosphere, and life during the first 4-billion-years of the planet's history is of great intellectual appeal and deserves continued emphasis. Nonetheless, of greatest practical value are studies of global change during the most recent interval of geological time. The geological record of the past 10,000 years has great potential for shedding light on the ways in which climatic changes affect life. In light of the global warming anticipated for the coming decade, warm intervals of the past should be scrutinized for possible lessons for the future. In addition, intervals exhibiting large-scale environmental change or mass extinction of life warrant detailed scrutiny for patterns and causes.
The past few years have seen major advances in paleoclimatology and terrestrial paleogeography. Sedimentary indicators and fossil biotas, especially floras, continue to shed light on climates of the past, but there is also a need to refine the existing kaleidoscopic picture of changing continental configurations, especially for the long pre-Mesozoic (older than 66-million-years) interval of earth history. Global paleogeographic reconstructions must continue to be developed and refined in all possible ways, including paleogeographic interpretations, global paleobathymetric reconstructions, identification of accreted terranes and microcontinents both through anomalous fossil distributions and paleomagnetic determinations. Determination of the rates of geochemical cycling requires knowledge of the sizes, elevations, and positions of continents in the past.
Changing climatic regimes, plate positions, and levels of land and sea have had powerful effects on the thermal structure and current patterns of the world ocean. At the forefront of paleoceanography today are studies of the three-dimensional oceanic structure, including thermohaline circulation, conditions in the deep-sea, upwelling, and vertical zonation of plankton. The Ocean Drilling Program should continue to play a key role in this kind of research for the most recent 150-million-years of