scispace - formally typeset
Search or ask a question

Showing papers in "Annual Review of Earth and Planetary Sciences in 2007"


Journal ArticleDOI
TL;DR: The recent past may be insufficient for prediction, however, as feedbacks between the carbon cycle and climate become more prominent as mentioned in this paper, leading to more accurate predictions of future concentrations of CO2 and more accurate prediction of the rate and extent of climate change.
Abstract: The global carbon budget is, of course, balanced. The conservation of carbon and the first law of thermodynamics are intact. “Balancing the carbon budget” refers to the state of the science in evaluating the terms of the global carbon equation. The annual increases in the amount of carbon in the atmosphere, oceans, and land should balance the emissions of carbon from fossil fuels and deforestation. Balancing the carbon budget is not the real issue, however. The real issue is understanding the processes responsible for net sources and sinks of carbon. Such understanding should lead to more accurate predictions of future concentrations of CO2 and more accurate predictions of the rate and extent of climatic change. The recent past may be insufficient for prediction, however. Oceanic and terrestrial sinks that have lessened the rate of growth in atmospheric CO2 until now may diminish as feedbacks between the carbon cycle and climate become more prominent.

839 citations


Journal ArticleDOI
TL;DR: The Aral Sea is a huge terminal lake located among the deserts of Central Asia and has been repeatedly filled and dried, owing both to natural and human forces as discussed by the authors, and the most recent desiccation started in the early 1960s and owes overwhelmingly to the expansion of irrigation that has drained its two tributary rivers.
Abstract: The Aral Sea is a huge terminal lake located among the deserts of Central Asia. Over the past 10 millennia, it has repeatedly filled and dried, owing both to natural and human forces. The most recent desiccation started in the early 1960s and owes overwhelmingly to the expansion of irrigation that has drained its two tributary rivers. Lake level has fallen 23 m, area shrunk 74%, volume decreased 90%, and salinity grew from 10 to more than 100g/l, causing negative ecological changes, including decimation of native fish species, initiation of dust/salt storms, degradation of deltaic biotic communities, and climate change around the former shoreline. The population residing around the lake has also been negatively impacted. There is little hope in the foreseeable future to fully restore the Aral Sea, but measures to preserve/rehabilitate parts of the water body and the deltas are feasible.

576 citations


Journal ArticleDOI
TL;DR: The history of the southern central Andes, including the world's second largest plateau and adjacent intermontane basins and ranges of the Eastern Cordillera and the northern Sierras Pampeanas of Argentina and Bolivia, impressively documents the effects of tectonics and topography on atmospheric circulation patterns, the development of orographic barriers, and their influence on erosion and landscape evolution at various timescales as discussed by the authors.
Abstract: The history of the southern central Andes, including the world’s second largest plateau and adjacent intermontane basins and ranges of the Eastern Cordillera and the northern Sierras Pampeanas of Argentina and Bolivia, impressively documents the effects of tectonics and topography on atmospheric circulation patterns, the development of orographic barriers, and their influence on erosion and landscape evolution at various timescales. Protracted aridity in the orogen interior has facilitated the creation and maintenance of the Puna-Altiplano plateau. Contraction and range uplift, filling of basins, and possibly wholesale uplift of the plateau increased gravitational stresses in the orogen interior, which caused the eastward migration of deformation into the foreland and successive aridification. The uplift of the Andean orogen has also had a far-reaching influence on atmospheric and moisture-transport patterns in South America. This is documented by the onset of humid climate conditions on the eastern side of the Andes in late Miocene time, which was coupled with the establishment of dramatic precipitation gradients perpendicular to the orogen, and changes in tectonic processes in the Andean orogenic wedge.

372 citations


Journal ArticleDOI
TL;DR: Isotopic fingerprinting has been used to trace magmatic processes and the components that contribute to magmas as mentioned in this paper, and the relationship between isotopic composition and petrographic features, such as dissolution surfaces, can be used to constrain magma evolution pathways involving open system processes.
Abstract: Isotopic fingerprinting has long been used to trace magmatic processes and the components that contribute to magmas. Recent technological improvements have provided an opportunity to analyze isotopic compositions on the scale of individual crystals, and consequently to integrate isotopic and geochemical tracing with textural and petrographic observations. It has now become clear that mineral phases are commonly not in isotopic equilibrium with their host glass/groundmass. Isotopic ratios recorded from core to rim of a mineral grain reflect the progressive changes in the magma composition from which the mineral crystallized. The sense of these changes and the relationship between isotopic composition and petrographic features, such as dissolution surfaces, can be used to constrain magma evolution pathways involving open system processes such as magma mixing, contamination and recharge.

371 citations


Journal ArticleDOI
TL;DR: Finite element analysis has much potential in addressing questions of form-function relationships, providing appropriate questions are ask, and explicit hypothesis-testing bridges these two standpoints.
Abstract: Finite element analysis (FEA) is a technique that reconstructs stress, strain, and deformation in a digital structure. Although commonplace in engineering and orthopedic science for more than 30 years, only recently has it begun to be adopted in the zoological and paleontological sciences to address questions of organismal morphology, function, and evolution. Current research tends to focus on either deductive studies that assume a close relationship between form and function or inductive studies that aim to test this relationship, although explicit hypothesis-testing bridges these two standpoints. Validation studies have shown congruence between in vivo or in vitro strain and FE-inferred strain. Future validation work on a broad range of taxa will assist in phylogenetically bracketing our extinct animal FE-models to increase confidence in our input parameters, although currently, FEA has much potential in addressing questions of form-function relationships, providing appropriate questions are ask...

367 citations


Journal ArticleDOI
TL;DR: The electron microprobe can be used to characterize the geometry of compositional domains, analyze the composition of each domain, and, when carefully configured, determine the U-Th-total Pb age for domains as small as 5 μm in width as mentioned in this paper.
Abstract: Monazite is a light rare earth element (LREE)-bearing phosphate mineral that is present in a wide variety of rock types, has an extremely variable composition reflecting host rock conditions, and is a robust geochronometer that can preserve crystallization ages through a long history of geological events. Monazite crystals typically contain distinct compositional domains that represent successive generations of monazite, which in turn, can provide a detailed record of the geologic history of its host rocks. The electron microprobe can be used to characterize the geometry of compositional domains, analyze the composition of each domain, and, when carefully configured, determine the U-Th-total Pb age for domains as small as 5 μm in width. These data allow the monazite to be linked with, and place timing constraints on, silicate processes in the host rocks. Current applications span a broad range of geologic processes in igneous, metamorphic, hydrothermal, and sedimentary rocks.

347 citations


Journal ArticleDOI
TL;DR: In this paper, the basis of stable isotope fractionation as it applies to transition metals and metalloids is reviewed, analytical considerations, and the current status and future prospects of this rapidly developing research area.
Abstract: Considered esoteric only a few years ago, research into the stable isotope geochemistry of transition metals is moving into the geoscience mainstream. Although initial attention focused on the potential use of some of these nontraditional isotope systems as biosignatures, they are now emerging as powerful paleoceanographic proxies. In particular, the Fe and Mo isotope systems are providing information about changes in oxygenation and metal cycling in ancient oceans. Zn, Cu, Tl, and a number of other metals and metalloids also show promise. Here we review the basis of stable isotope fractionation as it applies to these elements, analytical considerations, and the current status and future prospects of this rapidly developing research area.

301 citations


Journal ArticleDOI
TL;DR: In this article, the authors provide a theory behind the application of stable isotope-based approaches to paleoaltimetry and apply this theory to test cases using modern precipitation and surface water isotopic compositions to demonstrate that it generally accords well with observations.
Abstract: The quantitative estimation of paleoaltitude has become an increasing focus of Earth scientists because surface elevation provides constraints on the geodynamic mechanisms operating in mountain belts, as well as the influence of mountain belt growth on regional and global climate. The general observation of decreasing δ18O and δ2H values in rainfall as elevation increases has been used in both empirical and theoretical approaches to estimate paleoelevation. These studies rely on the preservation of ancient surface water compositions in authigenic minerals to reconstruct the elevation at the time the minerals were forming. In this review we provide a theory behind the application of stable isotope-based approaches to paleoaltimetry. We apply this theory to test cases using modern precipitation and surface water isotopic compositions to demonstrate that it generally accords well with observations. Examples of the application of paleoaltimetry techniques to Himalaya-Tibet and the Andes are discussed ...

294 citations


Journal ArticleDOI
TL;DR: The Tongbai-Dabie-Sulu (east-central China)-Imjingang-Gyeonggi (central Korea)-Renge-Suo (Southwestern Japan)-Sikhote-Alin orogen along the paleo-Pacific edge of cratonal Asia.
Abstract: Convergent plate motion at ∼320–210 Ma generated the Tongbai-Dabie-Sulu (east-central China)-Imjingang-Gyeonggi (central Korea)-Renge-Suo (Southwestern Japan)-Sikhote-Alin orogen along the paleo-Pacific edge of cratonal Asia. This amalgamated belt reflects collision between the Sino-Korean and Yangtze cratons on the SW portion, and accretion of outboard oceanic arcs ± sialic fragments against the NE margin. Subducted Proterozoic-Paleozoic continental and oceanic crustal complexes underwent high- and ultrahigh-pressure metamorphism at low to moderate temperatures. Tectonic slices of sialic crust episodically disengaged from the downgoing plate and, driven by buoyancy, ascended rapidly to midcrustal levels from depths exceeding 90–200 km after continental collision in east-central China plus or minus Korea, and from ∼30–50 km after arrival of far-traveled oceanic terranes in SW Japan and the Russian Far East. On achieving neutral buoyancy and stalling out at 10–20 km depth, later doming, gravitation...

251 citations


Journal ArticleDOI
TL;DR: The C4 photosynthetic pathway as discussed by the authors is a series of structural and biochemical modifications around the more primitive C3 pathway that improve the photoynthetic efficiency under specific climatic conditions.
Abstract: The C4 photosynthetic pathway is a series of structural and biochemical modifications around the more primitive C3 pathway that improve the photosynthetic efficiency under specific climatic conditions. Hence, the origin and subsequent geographical expansion of the C4 plants likely reflects a record of climate change. Multiple paleoatmospheric pCO2 proxies indicate a critical CO2 threshold was breached ∼30 Ma, that potentially selected for CO2-concentrating mechanisms to overcome photorespiratory stresses imposed on the basic C3 pathway. Details of the C4 pathway's earliest origins remain enigmatic given the paucity of the geologic record. Nonetheless, δ13C proxy records from paleosol carbonates, ungulate teeth, and plant-derived compounds indicate C4 plants likely represented an important component of plant biomass by the Early Miocene. Low CO2 levels appear to be a precondition for the development of the C4 photosynthetic pathway; however, comparisons of δ13C proxy records indicate that the timin...

249 citations


Journal ArticleDOI
TL;DR: The Indian Ocean tsunami of 2004 resulted from a fault rupture more than 1000 km in length that included and dwarfed fault patches that had broken historically during lesser shocks as discussed by the authors, and such variation in rupture mode, known from written history at a few subduction zones is also characteristic of earthquake histories inferred from geology on the Pacific Rim.
Abstract: Histories of earthquakes and tsunamis, inferred from geological evidence, aid in anticipating future catastrophes. This natural warning system now influences building codes and tsunami planning in the United States, Canada, and Japan, particularly where geology demonstrates the past occurrence of earthquakes and tsunamis larger than those known from written and instrumental records. Under favorable circumstances, paleoseismology can thus provide long-term advisories of unusually large tsunamis. The extraordinary Indian Ocean tsunami of 2004 resulted from a fault rupture more than 1000 km in length that included and dwarfed fault patches that had broken historically during lesser shocks. Such variation in rupture mode, known from written history at a few subduction zones, is also characteristic of earthquake histories inferred from geology on the Pacific Rim.

Journal ArticleDOI
TL;DR: In this article, the impact of glaciers on biogeochemical cycles will be longlasting, as the legacy of glacial erosion processes continues as long as sediment yields are elevated, and more significant effects may be associated with silt deposited in loess and on continental margins.
Abstract: Glaciers affect biogeochemistry of landscapes through their sediments. Glacial erosion rates are high and the sediments produced are distinctively fine grained, hence glaciers can be thought of as producers of mineral surface area. Although this mineral surface area is highly reactive, temperature limits chemical weathering fluxes from glaciers and their surroundings. More significant effects may be associated with silt deposited in loess and on continental margins. Thick deposits in both settings contribute to carbon cycling through both silicate weathering and organic carbon burial. The impact of glaciers on biogeochemical cycles will be long-lasting, as the legacy of glacial erosion processes continues as long as sediment yields are elevated.

Journal ArticleDOI
TL;DR: In the last ice age cycle and beyond, abrupt changes of North Atlantic deep water formation, North Atlantic sea ice extent, and widespread climate occurred repeatedly in response to changing freshwater fluxes and perhaps other causes.
Abstract: Linked, abrupt changes of North Atlantic deep water formation, North Atlantic sea ice extent, and widespread climate occurred repeatedly during the last ice age cycle and beyond in response to changing freshwater fluxes and perhaps other causes. This paradigm, developed and championed especially by W.S. Broecker, has repeatedly proven to be successfully predictive as well as explanatory with high confidence. Much work remains to fully understand what happened and to assess possible implications for the future, but the foundations for this work are remarkably solid.

Journal ArticleDOI
TL;DR: The authors assesses the evidence from both "proxy" climate data and theoretical climate model simulations with regard to the nature and causes of climate variability over a time interval spanning roughly the past two millennia.
Abstract: To assess the significance of modern climate change, it is essential to place recent observed changes in a longer-term context. This review assesses the evidence from both “proxy” climate data and theoretical climate model simulations with regard to the nature and causes of climate variability over a time interval spanning roughly the past two millennia. Evidence is reviewed for changes in temperature, drought, and atmospheric circulation over this timescale. Methods for reconstructing past climate from proxy data are reviewed and comparisons with the results of climate modeling studies are provided. The assessment provided affirms the role of natural (solar and volcanic) radiative forcing in past changes in large-scale mean temperature changes and in dynamical modes of climate variability such as the North Atlantic Oscillation (NAO) and El Ni ˜ no/Southern Oscillation (ENSO) influencing large-scale climate. At hemispheric scales, late twentieth century warmth appears unprecedented in the context of at least the past 2000 years. This anomalous warmth can only be explained by modern anthropogenic forcing.

Journal ArticleDOI
TL;DR: Trilobite evolution is consistent with an increased premium on effective enrollment and protective strategies, and with an evolutionary trade-off between the flexibility to vary the number of trunk segments and the ability to regionalize portions of the trunk.
Abstract: The good fossil record of trilobite exoskeletal anatomy and ontogeny, coupled with information on their nonbiomineralized tissues, permits analysis of how the trilobite body was organized and developed, and the various evolutionary modifications of such patterning within the group. In several respects trilobite development and form appears comparable with that which may have characterized the ancestor of most or all euarthropods, giving studies of trilobite body organization special relevance in the light of recent advances in the understanding of arthropod evolution and development. The Cambrian diversification of trilobites displayed modifications in the patterning of the trunk region comparable with those seen among the closest relatives of Trilobita. In contrast, the Ordovician diversification of trilobites, although contributing greatly to the overall diversity within the clade, did so within a narrower range of trunk conditions. Trilobite evolution is consistent with an increased premium on effective enrollment and protective strategies, and with an evolutionary trade-off between the flexibility to vary the number of trunk segments and the ability to regionalize portions of the trunk.

Journal ArticleDOI
TL;DR: The hemispheric dichotomy is a fundamental feature of Mars, expressed by a physiographic and geologic divide between the heavily cratered southern highlands and the relatively smooth plains of the northern lowlands as discussed by the authors.
Abstract: The hemispheric dichotomy is a fundamental feature of Mars, expressed by a physiographic and geologic divide between the heavily cratered southern highlands and the relatively smooth plains of the northern lowlands. The origin of the dichotomy, which may have set the course for most of the subsequent geologic evolution of Mars, remains unclear. Internally driven models for the dichotomy form the lowlands by mantle convection, plate tectonics, or early mantle overturn. Externally driven models invoke one giant impact or multiple impacts. Areal densities of buried basins, expressed by quasicircular depressions and subsurface echoes in radar sounding data, suggest that the dichotomy formed early in the geologic evolution of Mars. Tectonic features along the dichotomy boundary suggest late-stage modification by flexure or relaxation of the highlands after volcanic resurfacing of the northern lowlands. Subsequent deposition and erosion by fluvial, aeolian, and glacial processes shaped the present-day dichotomy boundary.

Journal ArticleDOI
TL;DR: Burning has been a near-continuous feature of the Australian environment but has become progressively more important since the mid-Tertiary, associated with the development of the characteristic sclerophyll vegetation as discussed by the authors.
Abstract: Burning has been a near-continuous feature of the Australian environment but has become progressively more important since the mid-Tertiary, associated with the development of the characteristic sclerophyll vegetation. In the Quaternary, the extent of burning has varied temporally and regionally with glacial-interglacial cyclicity. Burning during glacial periods was reduced in drier areas, presumably because of a critical reduction in fuel availability, but increased in relatively wetter areas where fuel levels were high. On both glacial and Holocene timescales, peaks in charcoal often accompany transitions between fire-insensitive vegetation types, suggesting that burning is facilitated during periods of climate change and environmental instability. This suggestion has been supported by the demonstration of close relationships between fire and El Nino activity. Burning has also increased progressively over the past few hundred thousand years with major accelerations around the time of first human...

Journal ArticleDOI
TL;DR: The Fossil Forest site, located on Axel Heiberg Island, Canada, has yielded a particularly rich assemblage of plant macro- and micro-fossils, as well as paleosols, all exquisitely preserved as mentioned in this paper.
Abstract: Lush forests, dominated by deciduous conifers, existed well north of the Arctic Circle during the middle Eocene (∼45 Ma). The Fossil Forest site, located on Axel Heiberg Island, Canada, has yielded a particularly rich assemblage of plant macro- and microfossils, as well as paleosols—all exquisitely preserved. Methods ranging from classical paleobotany, to stable-isotope geochemistry, have been applied to materials excavated from the Fossil Forest and have revealed layers of diverse conifer forests with a rich angiosperm understory that successfully endured three months of continuous light and three months of continuous darkness. Paleoenvironmental reconstructions suggest a warm, ice-free environment, with high growing-season-relative humidity, and high rates of soil methanogenesis. Methods to evaluate intraseasonal variability highlight the switchover from stored to actively fixed carbon during the short annual growing season.

Journal ArticleDOI
TL;DR: The morphology of passive continental shelves is dictated by the input of sediments from rivers and their redistribution by waves, currents, and gravity-driven flows as discussed by the authors, and the pathways followed by sediments sculpt a landscape whose diversity is rarely matched on Earth's surface.
Abstract: The morphology of passive continental shelves is dictated by the input of sediments from rivers and their redistribution by waves, currents, and gravity-driven flows. The pathways followed by sediments sculpt a landscape whose diversity is rarely matched on Earth's surface. Sediments are released to the shelf from triangularly shaped, elongated, and dendritic deltas. Barrier islands rise from gently sloping areas, tidal channels dissect flats and saltmarshes, fine sediments form broad convex deposits, and shallow submarine valleys convey sediments and water to the deep ocean. This morphological diversity is based on two main building elements: water and sediments. Fluxes of water and sediments are particularly suitable to be modeled with numerical methods based on the continuum hypothesis and hydrodynamics theory. In recent years, a series of models have been developed to explore and understand the formation of shelf landforms from the dynamics of sediment transport. Herein we present an overview ...

Journal ArticleDOI
TL;DR: In this article, the authors show that some reaction classes at mineral surfaces are surprisingly robust and treatable using kinetic information in hand, such as dissociation of the oxygens that bridge metals and that hold the structure together.
Abstract: Earth scientists will come to rely heavily upon computational chemistry because our environments are so difficult to sample. Essential geochemical information can often be better acquired by simulation than by either experiment or field sampling. No reactions are more essential to geochemistry than those involving water. Considerable advances are being made in understanding these hydrolytic reactions by close coupling of simulation to experiments on 1–5-nmsized metal-hydroxide clusters. These clusters are sufficiently small that experiments can identify reaction properties at specific metaloxygen sites that can then be treated using high-level methods of simulation. This twofold approach shows that some reaction classes at mineral surfaces are surprisingly robust and treatable using kinetic information in hand. Pathways for other reactions, such as dissociation of the oxygens that bridge metals and that hold the structure together, are enormously sensitive to details that neither experiment, nor simulation, alone can fully uncover. New efforts are needed to synthesize 1–5 nm experimental molecules to predict rate parameters for these aqueous reactions.

Journal ArticleDOI
TL;DR: In this paper, the authors present an overview of how noninvasive geophysical methods can be used for this purpose, focusing on monitoring mechanical properties, fluid transport, and biogeochemical processes.
Abstract: Geophysical methods can be used to create images of the Earth’s interiorthatconstitutesnapshotsatthemomentofdataacquisition.In manyapplications,itisimportanttomeasurethetemporalchangein the subsurface, because the change is associated with deformation, fluid flow, temperature changes, or changes in material properties. We present an overview of how noninvasive geophysical methods can be used for this purpose. We focus on monitoring mechanical properties, fluid transport, and biogeochemical processes, and present case studies that illustrate the use of geophysical methods for detecting time-lapse changes in associated properties.

Journal ArticleDOI
TL;DR: The etiology of many chronic diseases from exposure to earth materials (asbestos disease, As-and Se-induced cancers, and other disabilities) are suspected, but precise mechanisms of induction are presently unknown as mentioned in this paper.
Abstract: Insidious hazards that affect humans and other living creatures are addressed in this review. Debilitation and disease that may arise from naturally occurring gases, minerals, and elements create problems with characteristics that inhibit progress toward adequate and immediate solutions: (a) Human or animal reactions are delayed, not detected until long after the original exposure; (b) sporadic or continual low-level exposures to the minor or trace amounts of offending materials via the atmosphere, hydrosphere, and lithosphere are difficult to evaluate; (c) the air, water, and food consumed may contain hazardous substances that go unnoticed; and (d ) health reactions depend on bioavailability of the hazard and susceptibility of the individual. The etiology of many chronic diseases from exposure to earth materials—asbestos disease, As- and Se-induced cancers, and other disabilities—are suspected, but precise mechanisms of induction are presently unknown. Stipulation of disease from Earth-based hazardous materials requires collaboration of Earth and biomedical scientists to avert, or at least ameliorate, future disease and debilitation.