Basic Research Opportunities in Earth Science (2001)

Human society is built upon a terrestrial foundation. Forests, farmlands, and cities are rooted in the Earth, and people draw sustenance from its outer layers in the form of water, food, minerals, and fuels. Earth science is thus a practical enterprise on which our society’s survival depends. It is also a fundamental quest for understanding the natural world—an exploration to learn about the origin, evolution, and future of our planetary home. Curiosity about these basic issues sustains scientific inquiry even in areas where the utility of the research is less than obvious.

In fact, the fundamental and practical aspects of Earth science are intimately interwoven. Seismological and potential-field techniques developed for finding oil and minerals are now employed to image churning structures thousands of kilometers deep within the Earth’s connecting mantle. These great thermal currents continually rejuvenate the face of Earth through plate tectonics, raising mountains, and causing earthquakes and volcanic eruptions. Helical motions even deeper, within the liquid outer core, generate the magnetic field that guides the compass and helps to shield the Earth’s biosphere from solar and cosmic radiation. Efforts to simulate the deep-seated machinery of mantle convection and the core dynamo are stretching the limits of computing technology and providing a dynamical framework for synthesizing many previously disparate observations. On a more local scale, the methods of analytical geochemistry developed for the study of minerals, rocks, and soils have become powerful weapons in the fight against toxic pollution. Ultraprecise positioning techniques of space geodesy have measured the continental drift postulated by Wegener; they now monitor the accumulation of strain across dangerous faults such as California’s San

Andreas, as well as maintain the reference grids used by land surveyors. Probing the Earth’s past through a detailed reading of the geological record is furnishing information about the behavior of climate and ecological systems that will be crucial to a future in which human activities become ever more potent forces of global environmental change.

The linkage between basic and applied research is growing stronger because some of the toughest problems facing the United States and the world at large require a deep understanding of the physical, chemical, and biological processes that govern terrestrial systems. These practical issues cannot be addressed successfully without a vigorous program of basic research across the full spectrum of Earth science. Moreover, they call for substantial enhancements in the methodologies for integrating observations from the various disciplines into system-level models with predictive capabilities. Given the improved technical means for acquiring vast new data sets and modeling complex dynamic systems, the opportunities for furthering these aspects of the Earth science agenda have never been better.

Four federal departments and three independent federal agencies have significant activities in Earth science ( Appendix A ). These organizations support a mixture of basic and applied research, including multidisciplinary studies of mission-oriented problems ranging from environmental remediation and climate change assessment to anticipating the behavior of active faults and volcanoes. The National Science Foundation (NSF) plays a crucial role in this milieu as the sole agency whose primary mission is basic research and education. Only the NSF, through its Earth Science Division (EAR), provides significant funding for investigator-driven, fundamental research in all of the core disciplines of Earth science. ¹

The future of EAR is important because this NSF division now shoulders an increasing burden of the national effort in basic Earth science ( Figure 1.1 ). In terms of buying power, the annual expenditures of EAR have grown about a factor of two during the last 20 years, reaching $97 million in 1999 (see Appendix A for a breakdown). However, the past few years have seen a substantial decline in the support of Earth science by other federal

organizations. According to NSF’s Federal Funds Survey, overall funding in basic Earth science fell from $555 million in 1993 to $388 million in 1997. When corrected for inflation, this amounts to a 37% reduction in federally supported basic research. EAR’s share of basic research rose concomitantly, from 14% in 1993 to 24% in 1997. More than ever, Earth science in the United States depends on the ability of EAR to support research initiatives.

FIGURE 1.1 Total annual federal obligations for basic Earth science (blue lines) and applied Earth science (red lines), compared to the annual budget of NSF’s Earth Science Division (black lines), in as-spent dollars (dashed lines) and constant 1997 dollars (solid lines). Since 1993, overall federal funding of Earth science has dropped substantially. SOURCE: Federal Funds Survey.

In this report, the Committee on Basic Research Opportunities in the Earth Sciences identifies areas of high-priority research within the purview

of the Earth Science Division of NSF, assesses cross-disciplinary connections, and discusses the linkages between basic research and societal needs. Some general perspectives on these topics are given in this introductory chapter. The current EAR program is described in Appendix A . Chapter 2 (“ Science Opportunities ”) surveys emerging fields of research and major scientific objectives that can now be addressed because of advances in theory, instrumentation, models, and data analysis. The committee’s assessment of these science opportunities draws on the literature, workshop reports, direct experience, and letters from individuals. The names of committee correspondents and workshop reports are given in Appendix B . In Chapter 3 (“ Findings and Recommendations ”), the committee compares the science goals described in Chapter 2 with the stated objectives of EAR and suggests new programmatic directions where needed. The rationale for the initiatives is laid out in the context of the current NSF structure, with particular emphasis on potential interconnections, both within and outside the EAR programs.

NSF-sponsored basic research generates new understanding about the Earth that applies directly to national strategic needs. Basic research in Earth science affects human welfare in five major areas:

1. discovery, use, and conservation of natural resources—fuels, minerals, soils, water,

2. characterization and mitigation of natural hazards—earthquakes, floods and droughts, landslides, tsunamis, volcanoes,

3. geoscience-based engineering—urban development, agriculture, materials engineering,

4. stewardship of the environment—ecosystem management, adaptation to environmental changes, remediation, and moderation of adverse human effects, and

5. terrestrial surveillance for national security—arms control treaty verification, precise positioning, mapping, subsurface remote sensing.

Many of these strategic issues concern the near-surface environment, where interactions between rock, soil, air, water, and biota determine the availability of nearly every life-sustaining resource. This special interfacial region of mass and energy flux, which comprises terrestrial, lacustrine, and marine components of the uppermost continental crust, is here called the “Critical Zone.” The Critical Zone is one of two primary loci of life on this

planet and the environment for most human activity. The other major locus of life is the sea, but even there, the flux of nutrients from the Critical Zone is essential. Processes within the Critical Zone mediate the exchange of mass and energy; they are thus essential to biomass productivity, nutrient balance, chemical recycling, and water storage, and they ultimately determine the content of the geological record.

The world’s population reached 6 billion in 1999 and is increasing by more than 200,000 people per day. This populace requires food, fuels, raw materials, and water in ever-increasing quantities. Developing new technologies to deliver these resources depends on progress in many areas of Earth science.

Global energy consumption rose from 344 quadrillion British thermal units (BTUs) in 1990 to 376 quadrillion BTUs in 1995. The Department of Energy projects that this total will grow by an average of 2.1% per year until 2020. The reliance on fossil fuels is not likely to change appreciably during the next decade. ² Oil consumption is expected to grow at an annualized rate of 1.8%, while natural gas usage will rise at 3.3%, faster than any other primary energy source. Worldwide, the burning of coal is likely to increase nearly as rapidly (3.0%), driven by energy demands in China, India, and other Asian countries. ³

Historically, most of the research and development (R&D) related to the extraction of fossil fuels has been supported by the petroleum and mining industries, rather than by federal agencies. A worldwide oil glut that began in 1983 triggered a restructuring of the petroleum industry, reducing the industry’s investments in basic research and its demand for Earth science professionals. Between 1991 and 1995, the petroleum refining and extraction industry reported cutbacks of 29% in R&D expenditures. The recent spate of

mergers among the major companies (BP-Amoco, Exxon-Mobil) is leading to further consolidations of the industry’s research activities. Nevertheless, the petroleum industry remains the largest employer of Earth scientists. ⁴ The short-term restrictions in the hiring of new Earth scientists have skewed the demographics, so that the petroleum companies will face problems in rejuvenating their professional science staffs. In the United States, this rejuvenation will depend heavily on graduates from research programs in Earth science supported by EAR.

Reservoir modeling, at the heart of modern optimization of oil and gas production, illustrates the link between basic and applied research. It involves the detailed characterization of hydrocarbon reservoirs and fluid properties at depth, and the use of large numerical simulations of multiphase fluid-flow to integrate many types of measurements (e.g., characterization of deep strata by three-dimensional seismic imaging and in situ well logging as a function of time) into predictive models of reservoir performance. Basic studies of fluid-rock interactions within petroleum reservoirs have much in common with investigations of a wide variety of hydrological, magmatic, and metamorphic systems in the upper crust. Given the commonality of processes among the various fluid reservoirs in the Critical Zone, the nation’s energy industry has a major stake in the basic research sponsored by EAR.

The worldwide consumption of non-food, non-fuel raw materials was about 10 billion tons in 1995, almost double the amount in 1970. About 62% of these goods were construction materials such as crushed stone, sand, and gravel; 16% were industrial minerals; 7% metals; 6% nonrenewable organics; and 9% agricultural and forestry products. ⁵ The search for mineral resources is a geological activity, and the results have been spectacularly successful. Improvements in the techniques for finding and exploiting these natural resources have combined with the efficiency of global markets to make shortages in strategic materials rare. Earth science has been instrumental in transforming once-scarce raw materials into readily available, low-cost commodities.

A wide range of Earth science research—from the basic chemistry and physics of mass transfer to the global tectonic framework—has contributed

to the development of geological models of ore-forming systems. Recent discoveries of significant ores have been strongly influenced by a basic understanding of Earth processes, including diamonds (mantle petrology), magmatic nickel (large igneous provinces), copper deposits (fluid-rock interaction), volcanic-hosted massive sulfide deposits (seafloor hydrothermal systems), and sediment-hosted lead-zinc deposits (basin-scale hydrology). Future discoveries may result from a better understanding of the physical, chemical, and biological processes involved in the formation and preservation of ore systems. Because the spatial and temporal distribution of mineral resources is highly variable, a key problem is to determine what controls the distribution of oregrade mineralization. Large deposits of tungsten-tin and copper ( Figure 1.2 ) are associated with periods of global arc volcanism, for example, but it remains unclear whether special conditions were necessary to create large upper crustal magma chambers or to trigger fluid release required to produce the ore. Research is also needed to determine the role of microbes in the modification and dispersion of ores in magmatic systems and associated hydrothermal environments, and the biological influences on the formation of sedimentary iron and uranium. Detailed, atomic-scale investigations of minerals, fluids, and mineral-fluid interfaces play a central role in this domain. However, with the continued success of science-based exploration, perhaps the greatest challenges for Earth scientists are not to find more resources— although this will surely remain important—but to produce them more efficiently and safely, to mitigate long-term environmental impacts, and to provide a scientific basis for long-term land-use decisions.

According to the United Nations Environment Program, more than one-third of all people are without a safe water supply, and one-quarter will suffer from chronic water shortages during the next decade. By 2025, it is projected that 15 countries worldwide will have encountered water stress (i.e., consumption levels exceeding 20% of available supply), 9 will suffer from water scarcity, and 22 will have run up against a “water barrier” to further development. ⁶

Informed decision making on water resources requires knowledge of the complex hydrologic systems operating within the Critical Zone and a predictive understanding of how they respond to natural and human modifications. At the Science and Technology Center (STC) for Sustainability of Semi-Arid

Hydrology and Riparian Areas, EAR’s newest STC, the University of Arizona and its partners ⁷ seek to move scientific knowledge about these issues from research groups to the agencies responsible for managing water resources. The storage and flux of water in the Critical Zone are multidisciplinary problems that connect hydrology to the study of the oceans and atmosphere and to the solid Earth. On the geological side, the investigation of aquifers and groundwater systems now relies extensively on the use of geochemical and geobiological techniques, as well as geophysical methods. Such techniques have been used to investigate the cause and distribution of elevated levels of arsenic in groundwater, for example, which pose a serious health hazard in many parts of the world. The problem is particularly acute in Bangladesh, where groundwater provides 97% of the drinking water supply. Because contamination is localized, data from hydrogeological (groundwater flow velocities and directions), geophysical (resistivity, seismic), and geochemical (isotopic, trace element chemistry) techniques will help guide the placement of new wells that draw water with acceptable concentrations of arsenic. ⁸

Soils are an immense and valuable natural resource. In their most obvious capacity, they serve as the foundation and primary reservoir of nutrients for agriculture and the ecosystems that produce renewable natural resources, but soils are also fundamental for waste disposal and water filtration, and as raw materials for construction and manufacturing activities. More generally, these biologically active, intricately structured, porous media—collectively called the pedosphere—mediate most of the life-sustaining interactions among the land, its surface waters, and the atmosphere. Organic carbon is recycled to the atmosphere through soils; about 25% of atmospheric carbon dioxide comes from soil biological oxidation reactions in the pedosphere, which contains twice as much carbon as the atmosphere and up to three times the carbon in all vegetation. Soils have a major influence on the hydrologic cycle.

The water most people use comes from groundwater, streams, and lakes; regardless of its pathway, water quality is determined largely by the soils it passes through.

Soil management is thus crucial to sustaining and improving the human habitat, and issues related to land use, soil quality, degradation, and contamination now figure prominently in most policy decisions germane to the Critical Zone. The attributes of soil, coupled with climate variables, have traditionally been used in agriculture to predict the potential and limitations of land areas to produce food, feed, or fiber, but these same concepts are now being applied to all types of ecosystems. Moreover, the application of high-input farming, especially on marginally arable lands, has accentuated the environmental problems related to soil erosion, soil degradation through acidification, accumulation of toxic elements and salinization, and downstream contamination of aquatic systems from agricultural runoff. In the United States, precision agriculture with site-specific management is being practiced extensively to counter detrimental effects, but much is yet to be learned.

Judicious soil management will require increasing investments in soil science, including research on the fundamental physical, chemical, and biological processes involved in soil development. This type of basic research fits very well into the larger agenda of NSF-sponsored Earth science. As a geological process, soil development demonstrates the power of weathering, which in turn is a key process for issues as diverse as the availability of nutrients, the emission and capture of greenhouse gases, the chemistry of the ocean, and the evolution and longevity of landscapes. How water flows through soil and interacts chemically with the pedosphere is fundamental to hydrology and climatology. Microbial processes in soil are a primary topic for novel research in geobiology, and the microscopic structure of soil is a new focus in the study of Earth materials. The opportunities to connect the study of soils to other aspects of geoscience through the basic research programs of EAR are therefore expanding.

The Critical Zone in which humans and many other biota live is a high-energy, often dangerous, interface. Here the solar-powered processes in the Earth’s fluid envelope interact with the tectonic processes powered by heat escaping from its deep interior. The atmosphere transports water from the oceans to the continents, where irregular patterns of rainfall and evaporation combine with the complex hydrological response of the land surface and its vegetation to produce a chaotic sequence of flooding and drought. The planetary heat flux drives plate tectonics and melts rock to form the magmas

that erupt in volcanoes. The plate motions accumulate stresses in the brittle part of the lithosphere, releasing strain energy through sudden failures on faults, causing earthquakes. Plate tectonics pushes up mountains and creates other topographic features, which release gravitational energy in the form of landslides and avalanches. When major landslides and earthquakes occur under the ocean, some of the potential energy that is released can propagate in the form of huge sea waves (tsunamis), inundating coastlines thousands of miles away.

Floods, droughts, severe storms, volcanic eruptions, earthquakes, landslides, and tsunamis compose a catalog of natural disasters that have wreaked destruction since the beginning of civilization. Only recently, however, has the changing nature of these threats been recognized. The process of urbanization begun in the Industrial Revolution continues apace; in 1950, only 3 out of 10 people lived in urban areas, while by 2030 this fraction will nearly double. As populations and the fragile infrastructures on which they depend concentrate in large urban areas, the risks of natural hazards, especially the economic risks, grow correspondingly. With regard to seismic hazard, Japan is fairly well prepared for earthquakes. Yet the modest-sized earthquake (magnitude 6.9) that struck Kobe on January 18, 1995, killed 5500 people and resulted in an economic loss of nearly $200 billion. According to one recent study, a repeat of the great 1923 Kanto earthquake (magnitude 7.9) would devastate modern Tokyo: the direct economic losses would total a staggering $2.1 trillion to 3.3 trillion, equivalent to 44-70% of Japan’s annual gross domestic product. ⁹ An event of this magnitude clearly would have an impact extending well beyond any one nation, affecting the entire global economy and thereby directly influencing the welfare and security of the United States.

On a worldwide basis, the problem of urban hazards is further amplified by the fact that the most severe natural disasters—earthquakes, hurricanes, typhoons, and volcanic eruptions—tend to be concentrated in low-latitude, coastal regions, where ambient environmental conditions support large populations and the current economic development is most intense. ¹⁰

Applied research on different types of natural hazards has a common set of practical objectives:

• education of the general populace about the threat of natural hazards and the steps that can be taken to reduce risks (public preparation),

• quantification of what will happen during a particular event scenario (deterministic hazard analysis) or over an ensemble of possible events (probabilistic hazard analysis)—both are used by engineers to reduce human casualties (safety engineering) and economic losses (performance-based engineering).

• specification of individual disasters in terms of where, when, and how large (event prediction)—in some cases, such as earthquakes and tsunamis, an accurate prediction of occurrence times may not be possible, in which case the objective of “when” may be weakened to “how frequently” (long-term forecasting), and

• accurate and timely information about the occurrence and circumstances of disastrous events for public notification (including early warning, when possible) and for use by government officials and emergency management personnel (rapid response).

Experience shows that these practical objectives are difficult to attain without precise observations and good understanding of the phenomena involved in natural hazards. Because the processes of magma motion through the upper crust can be detected and analyzed, the most dangerous volcanic eruptions can be predicted in a useful way. The 1991 eruption of Mt Pinatubo in the Philippines was forecast by the U.S. Geological Survey (USGS) early enough to allow the region to be evacuated and aircraft and other equipment to be removed from Clark Air Force Base. The forecasts are estimated to have saved 5000 to 20,000 lives and economic losses of at least $200 million. ¹¹ On the other hand, the most dangerous earthquakes cannot be predicted deterministically, because no reliable, precursory indicators of their timing, location, and magnitude have been discovered. Is this because such precursors do not exist or because the fault-rupture process is too poorly understood to know which kinds of behavior are most diagnostic of a large, impending event? These questions remain the subject of vigorous basic research, supported by EAR as part of NSF’s participation in the National Earthquake Hazard Reduction Program.

The role Earth science plays in civil and environmental engineering is often underappreciated. The foundations of cities, as well as the transportation networks that connect them and the lifelines of utilities that sustain them, are necessarily embedded in the Earth. The geology of the Earth’s surface therefore determines many aspects of how this development takes place, from the distribution of skyscrapers on Manhattan Island to the layout of freeways across the Los Angeles basin, both of which reflect fundamental geological structures. The geological problems of the “built environment” are the subject of geotechnical engineering, which is a major consumer of Earth science information. Geotechnical engineers must understand the short-term and long-term properties of soils, rocks, groundwater movement and composite geological formations, including their static strengths, responses to dynamic stresses and deformations, and degradation by weathering and other alterations. As urban areas develop and expand, these engineers are being called upon more frequently to slow down natural processes or even stop them from running their course. The challenges cataloged in one popular account ¹² include preventing the Atchafalaya River from capturing the Mississippi River to keep it flowing past New Orleans, stopping the encroachment of basaltic lava on a community in Iceland, and minimizing the impact of flooding and debris flows from the steep scarp of the San Gabriel Mountains adjacent to Los Angeles. Basic research furnishes the knowledge of Earth materials and processes needed to address these engineering challenges.

The study of Earth materials has contributed significantly to materials science and engineering. For example, the study of nanocrystals and biomaterials originated in research on soils and biominerals, and Earth scientists have pioneered the development of substances ranging from high-temperature superconductors to superhard materials. Moreover, they have been leaders in the development of new analytical technologies, ranging from ultraprecise isotopic measurements and atomic resolution imaging of minute particles to the application of synchrotron, neutron, and other major facilities to the study of complex natural substances. These sophisticated analytical and experimental techniques have been employed in applications ranging from the engineering of synthetics to novel methods for forensic investigations. Earth scientists have also led in research at ultrahigh pressures, with applications to the physics and chemistry of materials as well as to simulating the deep interiors of planets.

With the increase in world population, the Earth has seemingly shrunk from a vast realm of unspoiled lands and seas to a small blue planet with limited resources for sustaining human activities. Environmental concerns now factor into policy decisions on the extraction and production of energy and mineral resources, as well as the disposal of their waste products. A key environmental issue is the storage of radioactive products from the nuclear arms program of the Cold War, spent fuel rods from nuclear power plants, and high-level radioactive wastes from medicine and other applications. Continued research on the level of seismic and volcanic activity and the stability of the water table will be needed to ensure the isolation of long-lived radioactive waste in designated underground repositories such as Yucca Mountain. Materials studies, including at the microscopic scale, have played an important role in revealing the potential for containment within or leakage through both the engineered barriers and the natural media of prospective waste disposal sites.

Mining, milling, and in situ leaching also produce wastes that are toxic to living organisms. Hardrock mining of metalliferous deposits can release metals and chemicals such as cyanide to surface and groundwater and to aquatic ecosystems. Moreover, mining activities directly affect terrestrial ecosystems because they destroy habitat and alter migration patterns by creating barriers and fragmenting animal territories. Geochemical, hydrological, mineralogical, and microbiological research and monitoring will be key to mitigating these adverse effects. In dealing with these and other challenging problems of the near-surface environment, basic research is needed to achieve an understanding that reaches from the atomic scale, at which the detailed fluidflow patterns and the distribution of contaminants between fluids and solids are determined, to the scale of major geological features and hydrologic systems, which govern the regional containment and dispersal of contaminants.

On an even larger scale, human activities are now capable of causing substantial, if unintended, global environmental change. Anthropogenic contributions to rising atmospheric CO₂ and other greenhouse gas concentrations and their potential impact on future climate are issues of global economic and political significance. Earth science is playing a significant role in understanding the global carbon budget and key aspects of greenhouse forcing, not only in the present, but at longer time scales, which are accessible only through the geological record. Information on paleoenvironments, which is extensive but relatively unexploited, can be used to identify forcing factors that have controlled climate in the past, their variation over time, and the causes of rapid transitions in the climate state. In particular, geochemical, isotopic, and paleontologic analyses of marine sediments and fossils can be

used to infer the extent of glaciers and ice sheets, as well as the temperature and composition of the oceans. The abundance and range of species, the nature of the land cover, and the position of shorelines can be inferred from analysis of terrestrial sediments, soils, and fossils. Such research provides important constraints on climate models, which are extending increasingly into the geological past.

Earth science has found significant applications in the arenas of national defense and global security. A range of technologies based on Earth science are essential components in the global monitoring and verification of nuclear test bans, nuclear nonproliferation treaties, and other arms control measures. From the first multinational discussions in Geneva in the late 1950s, it has been recognized that reliable identification of small underground nuclear explosions is the primary technical issue confronting the verification of a comprehensive nuclear test ban treaty (CTBT). The resulting U.S. program in nuclear explosion seismology stimulated basic as well as applied research. To improve seismological detection and location capabilities, for example, the Department of Defense developed a 120-station World Wide Standardized Seismographic Network (WWSSN). The WWSSN sharpened the images of global seismicity, which played a significant role in the discovery of plate tectonics and yielded much better models of deep-Earth structure that in turn resulted in a better understanding of the Earth’s composition and internal dynamics.

After decades of negotiations, the CTBT was opened for signature on September 24, 1996, and has thus far been endorsed by 154 nations. Adherence to the treaty will be verified by the International Monitoring System (IMS). The IMS is a worldwide distribution of permanent stations designed to detect clandestine nuclear explosions by measuring wind-transported radionuclides and waves transmitted through the atmosphere (infrasound), oceans (hydroacoustic), and solid Earth (seismic). Basic research related to the hydroacoustic and infrasound networks will open new avenues of research in the Earth sciences (e.g., the infrasound network can be used to count meteorites). EAR-sponsored research related to the CTBT focuses primarily on seismology, although radionuclide and other geochemistry studies are also critical for verification of the CTBT and the Chemical Weapons Convention of 1993. Recent advances in particulate and isotopic analyses have considerable potential for improving the capabilities in radionuclide monitoring.

Earth science contributes to national security in a number of other ways. Precise geodetic measurements of the Earth’s topography, gravity field, and

the active deformation of its solid surface are crucial to military as well as civilian navigation. The electromagnetic properties of the solid Earth must be studied to determine their effects on global communications. On a much smaller spatial scale, electromagnetic sounding methods are employed by the military to detect unexploded ordnance. Geophysical remote sensing is used to gather intelligence on subsurface operations that require tunneling and other excavations.

The study of the Earth remains a true science of discovery. From the theory of evolution to the theory of plate tectonics, breakthroughs in this field have influenced deeply our thinking about the natural world, and there is every reason to believe that discoveries of similar significance will be made in the future, especially about events and processes still obscured in the Earth’s past or hidden at depths within its interior. Many great unsolved problems spring easily to mind: the origin of life; causes of rapid biological diversifications and extinctions; early evolution of the solar system and planetary accretion; segregation of the core, inner core and continents; workings of active fault systems; mechanisms of climate transitions; and extent of the deep biosphere. At the same time, it is important to recognize that scientific discoveries are not born in isolation, but usually arise in a context prepared by the continuing integration of new data into better models of how the world works. In Earth science, the rate of this synthesis has been accelerated by major improvements in three types of research capabilities: (1) techniques for deciphering the geological record of terrestrial change and extreme events, (2) facilities for observing active processes in the present-day Earth, and (3) computational technologies for realistic simulations of dynamic geosystems. Exploiting these capabilities and extending their range offer a new agenda for basic research.

A distinguishing feature of Earth science is its access to the planet’s unique history “written in stone.” This geological record comprises a wealth of information about terrestrial and extraterrestrial events and conditions, from the present back into the farthest reaches of time. It is preserved in the rocks and fossils of the continents, their margins, and the deep seafloor, as well as in a wide range of extraterrestrial materials collected in the form of meteorites, cosmic dust, and samples ferried by spacecraft from other bodies

in the solar system. ¹³ Sequences of sedimentary rocks record events on time scales ranging from the subannual to billions of years. Metamorphic rocks found in ancient continental regions yield radiometric ages of up to 4 billion years, and they document processes active when the Earth was still fresh from a Hadean period of planetary formation and bombardment. Meteorites extend this record back to the earliest events in the condensation of the solar nebula, 4.56 billion years ago, and minute samples of cosmic dust have been identified that push this chronicle even further back to the actual manufacturing of the chemical elements in earlier generations of stars.

The methods available for reconstructing the history of the Earth and its parent nebula have been greatly extended and improved. Entirely new techniques are now available from previously inaccessible isotopic systems; examples include the use of tungsten isotopes to constrain the timing of the segregation of the Earth’s metal core and osmium isotopes to date refractory mantle samples. Augmented capabilities have also come from substantial improvements to old techniques, such as recalibration of the carbon-14 method, and the use of accelerator mass spectrometry to extend its temporal resolution and reduce the requisite sample size.

State-of-the art analytical techniques promise to define much more precisely the timing, duration, and lateral extent of “extreme events,” which include major magmatic eruptions, large bolide impacts, unusual excursions in global climate, and collapses and reversals of the Earth’s magnetic field. During these rare occurrences, conditions at the Earth’s surface have greatly exceeded their usual range, and they have therefore exerted a disproportionate influence on the evolution of the planet and its biosphere. Absolute dates on the ages of individual units within geological formations can now be obtained from the uranium-lead and potassium-argon systems with sufficient precision (fractions of a percent) to estimate the duration of the Cambrian “explosion” (the sudden first appearance of macroscopic, skeleton-bearing life), the great mass extinction at the Permo-Triassic boundary, and the huge outpourings of magma (millions of cubic kilometers) in the form of flood basalts that have occurred at irregular intervals throughout Earth history.

Extreme events of short duration can be difficult to decipher because only a small fraction of history is preserved in the geological record. What happened must be inferred from fragmentary evidence, such as the sequence of sedimentary deposits (floods, mudflows, major storms), juxtapositioning

of different paleoenvironments (earthquakes), or characteristic mineralogy or chemistry (bolide impacts). On the other hand, extreme events of longer duration can be easier to recognize than smaller, more transient changes. Climatic extremes such as the “hothouse” conditions of the Cretaceous resulted in widespread bauxite deposits (lateritic weathering), petroleum generation (high marine stands and biologic productivity), and iron- and phosphorous-rich sedimentary rocks (marine upwelling). Precambrian mantle plumes have been postulated as the cause of the major magmatic eruptions that led to the formation of large igneous provinces and their associated mineral deposits, which are themselves chemical extremes.

Similarly, relatively recent extreme events are recognizable in sediment and ice cores. Analysis of such cores has led to a greater appreciation of the transient nature of climate change and the potential for abrupt and amplified responses following small perturbations in atmospheric and oceanic processes. For example, marine records from the Paleocene-Eocene boundary reveal an intense warming period, lasting no more than 10,000 years, associated with a large benthic extinction, changes in ocean circulation patterns, and increased ocean temperatures, especially in higher latitudes. Isotopic analysis suggests that a catastrophic release of methane, possibly from marine clathrates, resulted in a sharp increase in greenhouse warming. On land, soil and vertebrate fossil evidence links this event to the sudden onset of warm terrestrial climates and the first appearance of modern mammal lineages.

The combination of precise geochronology and systematic field investigations can reconstruct surprisingly complete and detailed accounts of what happened during major events in Earth history. One of the most fascinating detective stories in all of geoscience is the discovery of the Chicxulub crater off the Yucatan peninsula, the “smoking gun” that confirmed the Alvarez hypothesis that a bolide impact killed the dinosaurs at the end of the Cretaceous. ¹⁴ Research of this type is yielding an increasingly rich picture of Earth processes, which in turn is helping to assess the significance of future changes and extremes, the mechanisms that might trigger them, and the hazards to human life that could result.

Until recently, only rudimentary instrumentation was available for collecting synoptic data on global processes in real time, and the monitoring

of processes on regional and local scales was spotty at best. However, the ongoing “digital revolution” has significantly improved the observational capabilities of Earth science through the development of many new remotesensing and direct-sampling technologies. In addition, data-gathering efforts have been greatly facilitated by worldwide communication systems that can transmit high-resolution observations of many variables from remote locations in real or near-real time. Newly available technologies range from space-based platforms and global networks of surface observatories to extremely sensitive instruments that can measure Earth materials and processes in both the laboratory and the field.

Laser altimetry from aircraft can be combined with accurate digital elevation models to investigate the surficial processes of erosion and sedimentation at the meter scale. Interferometric synthetic aperture radar aboard satellites can map decimeter-level deformations of fault ruptures, magma inflation of volcanoes, and ground subsidence continuously over areas tens to hundreds of kilometers wide. These images of the strain field complement the even more precise, pointwise measurements from the satellite-based Global Positioning System (GPS). GPS receivers can be located with millimeter precision over baselines of thousands of kilometers and can thus be used to map long-term strain rates across wide plate boundaries, such as in the western United States, while arrays of GPS stations can be used to measure the short-term deformations associated with volcanoes and earthquakes.

Observing processes that are active beneath the solid surface is particularly challenging, because the Earth’s interior is inaccessible and characterized by extreme conditions. Rocks in the outer few kilometers of the crust can be sampled directly by trenching, tunneling, and drilling. Trenching to a depth of a few meters provides a means of studying environments (e.g., paleosols, fluvial systems) and processes (e.g., weathering, faulting) that operated in the relatively recent geological past. Paleoseismologists have made particularly effective use of trenching techniques to discover and date precisely the history of individual large earthquakes on major faults. Although laborious and expensive, drilling is often the best method for probing more deeply buried rock masses and collecting in situ measurements of active geological processes. Novel logging techniques developed by the petroleum industry, such as nuclear magnetic resonance and electromagnetic borehole imaging, are furnishing unparalleled data on the environments deep within sedimentary basins and continental basement rocks. The German KTB drilling project, which penetrated to a depth of 9100 m in 1994, furnished key insights into crustal processes, revealing the near-critical state of crustal stress predicted by Byerly’s relationship, which has important implications for earthquake mechanics. In addition, the project confirmed hydrostatic pore pressure at great depth in the Earth’s crust and detailed geochemical data provided

constraints on how the hydrological cycle operates. Samples from more recent deep drilling of a Hawaiian volcano are yielding a better understanding of the physics and chemistry of deep-seated sources of volcanism. Deep drilling of active faults such as the San Andreas offers great promise for elucidating earthquake processes, including the role of fluids in fault mechanics.

Earthquakes and controlled (artificial) seismic sources generate a variety of elastic waves that encode an immense amount of information about the Earth through which they propagate. This illumination can be captured on arrays of seismic sensors and digitally processed into three-dimensional images of Earth structure and moving pictures of earthquake ruptures. Seismology thus gives geoscientists the eyes to observe fundamental processes within the planetary interior. In the past 15 years, the NSF-funded Incorporated Research Institutions for Seismology (IRIS) have provided new tools of seismological imaging to a broadly based user community, and the results have transformed the study of the solid Earth. The USArray program, a part of the recently proposed EarthScope initiative, would greatly extend these seismological capabilities, allowing the Earth beneath North America to be imaged at much higher resolution than with existing instrumentation (see Chapter 2 , Box 2.2 ).

Measurements of the gravitational potential and electromagnetic fields constrain the mass variations and electrical properties of the interior, information that is complementary to seismological imaging and critical to its interpretation in terms of dynamic processes. The upcoming Gravity Recovery and Climate Experiment (GRACE) mission, for example, will measure the time-dependent component of gravity and thereby significantly advance studies of postglacial rebound, structure, and evolution of the crust and lithosphere; the hydrologic cycle; and mantle dynamics and plumes. ¹⁵

Geophysical interpretation also requires the understanding of Earth materials at the extreme pressures, high temperatures, and special chemical environments of the deep interior. Only by characterizing materials at these conditions can one translate the observations of remote sensing and geochemical sampling into a concrete understanding of the current state, evolution, and ultimately, origin of the planet. State-of-the-art laboratories and apparatus are needed for this purpose. Both static and dynamic (shockwave) methods are employed, with the NSF Center for High-Pressure Research (CHiPR) being a leader for the United States in the application of synchrotron facilities to static high-pressure experiments with diamond-anvil cells and multianvil presses. High-pressure techniques developed for the study of the deep interiors of the Earth and other planets now allow the

densities of solids and fluids to be changed by as much as an order of magnitude in the laboratory, revealing unforeseen properties while also producing new types of materials and supplying novel insights into condensed-matter physics ( Figure 1.3 ). ¹⁶

The chemical and isotopic composition of volcanic rocks on the Earth’s surface and of accidental inclusions of mantle rocks (xenoliths) in such lavas carries vast amounts of information on magma formation processes and the history responsible for the Earth’s chemically layered structure. The petrological and geochemical signatures of some xenoliths indicate that they have come from the midmantle transition zone and even the lower mantle, providing samples of the deep interior that can be studied directly in the laboratory. Advances in geochemical techniques and interpretation continue to expand and refine the understanding of chemical phenomena occurring within the mantle and core, both at the present time and in the distant geological past. Of particular interest is the increasing convergence between geochemical and geophysical approaches and the brightening prospects for a unified model of deep-Earth dynamics.

Measurement systems are now providing data on active Earth processes that are of unprecedented quality and quantity. To take full advantage of these rich sources of information, geoscientists will have to harness the power of advancing information technologies to collect and assemble raw data, to process and archive data products, and to make these products widely available to researchers and other users. A number of challenges can be identified: how to collect data in real time at modest cost from expanding global networks of sensors, many in remote locations; how to reconfigure networks for robust operation when components fail, emergencies arise, or demands peak; how to ensure prompt delivery of data to users with time-critical needs (e.g., rapid response to natural disasters) while maintaining quality control and accessibility by lower-priority users; how to process heterogeneous data streams quickly enough that the data volume does not overwhelm managers and users; how to archive data in a way that enhances research capabilities rather than leading to overfull data warehouses. This type of information management will require innovations in Internet connectivity, multimedia information processing, digital libraries, and visualization techniques. Geoscientists are in an excellent position to exploit and contribute to the research being done in all of these areas by the information technology communities.

ting their behaviors, can be of immense practical value; thus, achieving a predictive understanding has become a major research goal. Because most geosystems involve many components that interact nonlinearly over a wide spectrum of spatial and temporal scales, the behaviors they display are not amenable to classical theoretical analysis and manual calculation. Indeed, because of the rapidly expanding capabilities for observing terrestrial activity, the data volumes on geosystems will soon be measured in petabytes. The interpretation of such vast quantities of data lies beyond the expertise and ability of the lone scientist, requiring collaborations among large groups of investigators from a variety of disciplines. The primary integrative mechanism for this multidisciplinary activity is the system-level model.

Only in the past few years have computational capabilities permitted numerical simulations of an interesting spectrum of geosystem behaviors in three spatial dimensions. For instance, although the first attempts to model solid-state convection in the Earth’s mantle date from the early 1970s, the numerical resolution required to represent mantle convection properly in three dimensions was attained only in the 1990s. The first simulation of a self-sustaining core dynamo based on a realistic set of governing equations was not achieved until 1995. For some problems, such as simulations of active fault systems, full three-dimensional calculations over the appropriate scale range exceed the capabilities of even the largest available computers.

Continuing progress in geosystem modeling will depend heavily on improvements to the computational infrastructure of Earth science, including computational algorithms for exploiting parallel computers and other hardware, access to distributed computing and collaborative environments, advanced methods for code development and sharing, software libraries, visualization tools, and data management capabilities. The need for community models that can function as “virtual laboratories” for the study of particular geosystems presents a major challenge because new organizational structures will have to be set up to develop, verify, and maintain the requisite software components. The strategies and tools for this type of collaborative research are being developed by computer scientists in partnership with other research communities, and Earth scientists can learn and profit from participating in these efforts.

Most geosystems are so complex that the ability to extrapolate the observed behaviors into new regimes and confirm them with additional data becomes an essential measure of how well a system is understood. Predictions made from system-level models thus play an integral role in an iterated cycle of data gathering and analysis, hypothesis testing, and model improvement. The reliance on this type of model-based empiricism has significant implications for the organizational structure of geoscience, in addition to its epistemology, because it offers a framework for integrating

observations from many disciplines. In the study of active faulting, for example, geologists map faults, geomorphologists date fault motion, seismologists locate earthquakes, geodesists measure deformations, and rock mechanists investigate the frictional properties of fault materials. Numerical simulations of active fault systems attempt to bring together these various types of observations in the context of a self-consistent model. The success of such a model in reconciling diverse types of information can thus be used to confirm the compatibility of the data from different disciplines and ferret out inconsistencies, in addition to giving researchers confidence in their underlying assumptions and hypotheses.

The problems of relating observations and simulations are particularly difficult in the research fields sponsored by EAR, because the solid Earth is characterized by physical and chemical processes that generally have shorter ranges and longer durations than the fluid systems investigated by meteorologists and oceanographers. Two representative examples illustrate this point. First, the global circulation time is on the order of a month for the troposphere and about a thousand years for the deep ocean, but it exceeds 100 million years for mantle convection. Second, chemical diffusion is an important process both above and below the Earth’s solid surface, but the diffusivities of the common cations are 10 to 15 orders of magnitude lower in solid rock than in liquid water.

Fluid-bearing geosystems in the Critical Zone and upper crust—rock bodies containing magmas, petroleum, or water—present special challenges in this regard because the relevant processes range from the atomic level (i.e., sorption-desorption on mineral surfaces) to tens of kilometers or more. Their elucidation requires systematic, coordinated observations involving multiple disciplinary techniques that are spatially dense and extend over long time intervals. Field studies of this type are often most efficiently accomplished through the joint efforts of several groups of investigators in carefully chosen localities. Measurements and experiments within such “natural laboratories” may have to continue for many years. This mode of research is becoming more common as the trend toward the quantification of geological processes and system-level behaviors accelerates. Hence, the demand for basic research funds to invest in natural laboratories can be expected to increase.