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  • Big Time
    Annu. Rev. Earth Planet. Sci. (IF 9.235) Pub Date : 2019-05-30
    Paul F. Hoffman

    The Proterozoic Eon was once regarded as the neglected middle half of Earth history. The name refers to early animals, but they did not appear until the eon (2.5–0.54 Ga) was nearly over. Eukaryotic cells and sexual reproduction evolved much earlier in the eon, as did chloroplasts. Molecular dioxygen, the presence of which altered the geochemical behavior of nearly every element essential to life, rose from negligible to near-modern levels, and then plummeted before rising fitfully again. Plate tectonics took on a modern form, and two supercontinents, Nuna and Rodinia, successively congregated and later dispersed. Climate regulatory failures, i.e., Snowball Earth, appear to be a uniquely Proterozoic phenomenon, having occurred twice in rapid succession near the end of the eon (from 717 to 660 Ma and from 650 to 635 Ma) and arguably once near its beginning (ca. 2.43 Ga). Dynamic sea glaciers covered Snowball Earth oceans from pole to pole, and equatorial sublimation drove slow-moving ice sheets on land. Ultimately, the gradual accumulation of CO2 triggered rapid deglaciation and transient greenhouse aftermaths. Physically based and geologically tested, Neoproterozoic Snowball Earth appears to have molecular legacies in ancient bitumens and modern organisms. This is the story of my love affair with an eon that is now a little less neglected.

    更新日期:2019-12-31
  • Unanticipated Uses of the Global Positioning System
    Annu. Rev. Earth Planet. Sci. (IF 9.235) Pub Date : 2019-05-30
    Kristine M. Larson

    Global Positioning System (GPS) instruments are routinely used today to measure crustal deformation signals from tectonic plate motions, faulting, and glacial isostatic adjustment. In parallel with the expansion of GPS networks around the world, several new and unexpected applications of GPS have been developed. For example, GPS instruments are now being used routinely to measure ground motions during large earthquakes. Access to real-time GPS data streams has led to the development of better hazard warnings for tsunamis, flash floods, earthquakes, and volcanic eruptions. Terrestrial water storage changes can be derived from GPS vertical coordinate time series. Finally, GPS signals that reflect on the surfaces below a GPS antenna can be used to measure soil moisture, snow accumulation, vegetation water content, and water levels. In the future, combining GPS with the signals from the Russian, European, and Chinese navigation constellations will significantly enhance these applications. ▪ GPS data are now routinely used to study the dynamics of earthquake rupture. ▪ GPS instruments are an integral part of warning systems for earth- quakes, tsunamis, flash floods, and volcanic eruptions. ▪ Reflected GPS signals provide a new source of soil moisture, snow depth, vegetation water content, and tide gauge data. ▪ GPS networks can sense changes in soil moisture, groundwater, and snow depth and thus can contribute to water resource assessments.

    更新日期:2019-12-31
  • Dynamics in the Uppermost Lower Mantle: Insights into the Deep Mantle Water Cycle Based on the Numerical Modeling of Subducted Slabs and Global-Scale Mantle Dynamics
    Annu. Rev. Earth Planet. Sci. (IF 9.235) Pub Date : 2019-05-30
    Takashi Nakagawa; Tomoeki Nakakuki

    In this review, we address the current status of numerical modeling of the mantle transition zone and uppermost lower mantle, focusing on the hydration mechanism in these areas. The main points are as follows: (a) Slab stagnation and penetration may play significant roles in transporting the water in the whole mantle, and (b) a huge amount of water could be absorbed into the deep mantle to preserve the surface seawater over the geologic timescale. However, for further understanding of water circulation in the deep planetary interior, more mineral physics investigations are required to reveal the mechanism of water absorption in the lower mantle and thermochemical interaction across the core–mantle boundary region, which can provide information on material properties to the geodynamics community. Moreover, future investigations should focus on determining the amount of water in the early planetary interior, as suggested by the planetary formation theory of rocky planets. Moreover, the supplying mechanism of water during planetary formation and its evolution caused by plate tectonics are still essential issues because, in geodynamics modeling, a huge amount of water seems to be required to preserve the surface seawater in the present day and to not be dependent on an initial amount of water in Earth's system. ▪ Slab stagnation and penetration of the hydrous lithosphere are essential for understanding the global-scale material circulation. ▪ Thermal feedback caused by water-dependent viscosity is a main driving mechanism of water absorption in the mantle transition zone and uppermost lower mantle. ▪ The hydrous state in the early rocky planets remains to be determined from cosmo- and geochemistry and planetary formation theory. ▪ Volatile cycles in the deep planetary interior may affect the evolution of the surface environment.

    更新日期:2019-12-31
  • Atmospheric Escape and the Evolution of Close-In Exoplanets
    Annu. Rev. Earth Planet. Sci. (IF 9.235) Pub Date : 2019-05-30
    James E. Owen

    Exoplanets with substantial hydrogen/helium atmospheres have been discovered in abundance, many residing extremely close to their parent stars. The extreme irradiation levels that these atmospheres experience cause them to undergo hydrodynamic atmospheric escape. Ongoing atmospheric escape has been observed to be occurring in a few nearby exoplanet systems through transit spectroscopy both for hot Jupiters and for lower-mass super-Earths and mini-Neptunes. Detailed hydrodynamic calculations that incorporate radiative transfer and ionization chemistry are now common in one-dimensional models, and multidimensional calculations that incorporate magnetic fields and interactions with the interstellar environment are cutting edge. However, comparison between simulations and observations remains very limited. While hot Jupiters experience atmospheric escape, the mass-loss rates are not high enough to affect their evolution. However, for lower-mass planets, atmospheric escape drives and controls their evolution, sculpting the exoplanet population that we observe today. ▪ Observations of some exoplanets have detected atmospheric escape driven by hydrodynamic outflows, causing the exoplanets to lose mass over time. ▪ Hydrodynamic simulations of atmospheric escape are approaching the sophistication required to compare them directly to observations. ▪ Atmospheric escape sculpts sharp features into the exoplanet population that we can observe today; these features have recently been detected.

    更新日期:2019-12-31
  • The Sedimentary Cycle on Early Mars
    Annu. Rev. Earth Planet. Sci. (IF 9.235) Pub Date : 2019-05-30
    Scott M. McLennan; John P. Grotzinger; Joel A. Hurowitz; Nicholas J. Tosca

    Two decades of intensive research have demonstrated that early Mars (2 Gyr) had an active sedimentary cycle, including well-preserved stratigraphic records, understandable within a source-to-sink framework with remarkable fidelity. This early cycle exhibits first-order similarities to (e.g., facies relationships, groundwater diagenesis, recycling) and first-order differences from (e.g., greater aeolian versus subaqueous processes, basaltic versus granitic provenance, absence of plate tectonics) Earth's record. Mars’ sedimentary record preserves evidence for progressive desiccation and oxidation of the surface over time, but simple models for the nature and evolution of paleoenvironments (e.g., acid Mars, early warm and wet versus late cold and dry) have given way to the view that, similar to Earth, different climate regimes on Mars coexisted on regional scales and evolved on variable timescales, and redox chemistry played a pivotal role. A major accomplishment of Mars exploration has been to demonstrate that surface and subsurface sedimentary environments were both habitable and capable of preserving any biological record. ▪ Mars has an ancient sedimentary rock record with many similarities to but also many differences from Earth's sedimentary rock record. ▪ Mars’ ancient sedimentary cycle shows a general evolution toward more desiccated and oxidized surficial conditions. ▪ Climatic regimes of early Mars were relatively clement but with regional variations leading to different sedimentary mineral assemblages. ▪ Surface and subsurface sedimentary environments on early Mars were habitable and capable of preserving any biological record that may have existed.

    更新日期:2019-12-31
  • New Horizons Observations of the Atmosphere of Pluto
    Annu. Rev. Earth Planet. Sci. (IF 9.235) Pub Date : 2019-05-30
    G. Randall Gladstone; Leslie A. Young

    New Horizons data provide a snapshot of the current state of Pluto's atmosphere. Winds are slow and mostly controlled by sublimation of surface ices. Molecular nitrogen is the primary constituent below 1,800 km, while methane and carbon monoxide are important minor species. Photolysis of these gases leads to a thin haze that encompasses Pluto from the surface up to >500-km altitude and is important in heating and cooling the atmosphere. A cold (∼70 K) upper atmosphere curtails the escape of Pluto's molecular nitrogen to space, although there is substantial escape of methane (∼5 × 1025 molecules s−1), coincidentally about equal to its loss by photochemistry. It is unknown if the current atmosphere is representative of its long-term average state. From the inferred rapid rate of haze settling, it seems that Pluto's atmosphere must occasionally undergo collapse to allow time for radiation processing of the colorless haze material into the dark deposits found on the surface. ▪ This article outlines what has been gleaned about Pluto's atmosphere in the years since the New Horizons flyby. ▪ Pluto's atmosphere is most similar to Titan's—with the photochemistry of supervolatile nitrogen and hydrocarbons resulting in a kind of factory for cold haze production. ▪ Much has been learned about Pluto's atmosphere, but many new questions have arisen, and these will likely remain unanswered until there is a follow-up mission—no doubt a long time from now.

    更新日期:2019-12-31
  • The Compositional Diversity of Low-Mass Exoplanets
    Annu. Rev. Earth Planet. Sci. (IF 9.235) Pub Date : 2019-05-30
    Daniel Jontof-Hutter

    Low-mass planets have an extraordinarily diverse range of bulk compositions, from primarily rocky worlds to those with deep gaseous atmospheres. As techniques for measuring the masses of exoplanets advance the field toward the regime of rocky planets, from ultrashort orbital periods to Venus-like distances, we identify the bounds on planet compositions, where sizes and incident fluxes inform bulk planet properties. In some cases, the precision of measurement of planet masses and sizes is approaching the theoretical uncertainties in planet models. An emerging picture explains aspects of the diversity of low-mass planets, although some problems remain: Do extreme low-density, low-mass planets challenge models of atmospheric mass loss? Are planet sizes strictly separated by bulk composition? Why do some stellar characterizations differ between observational techniques? With the Transiting Exoplanet Survey Satellite (TESS) mission, low-mass exoplanets around the nearest stars will soon be discovered and characterized with unprecedented precision, permitting more detailed planetary modeling and atmospheric characterization of low-mass exoplanets than ever before. ▪ Following the Kepler mission, studies of exoplanetary compositions have entered the terrestrial regime. ▪ Low-mass planets have an extraordinary range of compositions, from Earth-like mixtures of rock and metal to mostly tenuous gas. ▪ The TESS mission will discover low-mass planets that can be studied in more detail than ever before.

    更新日期:2019-12-31
  • Destruction of the North China Craton in the Mesozoic
    Annu. Rev. Earth Planet. Sci. (IF 9.235) Pub Date : 2019-05-30
    Fu-Yuan Wu; Jin-Hui Yang; Yi-Gang Xu; Simon A. Wilde; Richard J. Walker

    The North China Craton (NCC) was originally formed by the amalgamation of the eastern and western blocks along an orogenic belt at ∼1.9 Ga. After cratonization, the NCC was essentially stable until the Mesozoic, when intense felsic magmatism and related mineralization, deformation, pull-apart basins, and exhumation of the deep crust widely occurred, indicative of destruction or decratonization. Accompanying this destruction was significant removal of the cratonic keel and lithospheric transformation, whereby the thick (∼200 km) and refractory Archean lithosphere mantle was replaced by a thin (<80 km) juvenile one. The decratonization of the NCC was driven by flat slab subduction, followed by a rollback of the paleo-Pacific plate during the late Mesozoic. A global synthesis indicates that cratons are mainly destroyed by oceanic subduction, although mantle plumes might also trigger lithospheric thinning through thermal erosion. Widespread crust-derived felsic magmatism and large-scale ductile deformation can be regarded as petrological and structural indicators of craton destruction. ▪ A craton, a kind of ancient continental block on Earth, was formed mostly in the early Precambrian (>1.8 Ga). ▪ A craton is characterized by a rigid lithospheric root, which provides longevity and stability during its evolutionary history. ▪ Some cratons, such as the North China Craton, can be destroyed by losing their stability, manifested by magmatism, deformation, earthquake, etc.

    更新日期:2019-12-31
  • Seawater Chemistry Through Phanerozoic Time
    Annu. Rev. Earth Planet. Sci. (IF 9.235) Pub Date : 2019-05-30
    Alexandra V. Turchyn; Donald J. DePaolo

    The major ion balance of the ocean, particularly the concentrations of magnesium (Mg), calcium (Ca), and sulfate (SO4), has evolved over the Phanerozoic (last 550 million years) in concert with changes in sea level and the partial pressure of carbon dioxide (pCO2). We review these changes, along with changes in Mg/Ca and strontium/calcium (Sr/Ca) of the ocean; how the changes were reconstructed; and the implication of the suggested changes for the overall charge balance of the ocean. We conclude that marine Mg, Ca, and SO4 concentrations are responding to different aspects of coupled tectonic changes over the Phanerozoic and the resulting effect on sea level. We suggest a broad conceptual model for the Phanerozoic changes in Mg, Ca, and SO4 concentrations along with the seawater 87Sr/86Sr and sulfur isotope composition. ▪ Marine concentrations of magnesium, sulfate, and calcium have varied over the last 550 million years in sync with changes in sea level and atmospheric carbon dioxide. ▪ Seawater chemistry and sea level both respond to supercontinent formation and breakup, age of the ocean floor, and extent of continental shelf area. ▪ Changes in plate tectonics impact the ocean's chemical balance and the carbon cycle in varied ways, resulting in cyclical changes in key climatic variables over geological time.

    更新日期:2019-12-31
  • Global Patterns of Carbon Dioxide Variability from Satellite Observations
    Annu. Rev. Earth Planet. Sci. (IF 9.235) Pub Date : 2019-05-30
    Xun Jiang; Yuk L. Yung

    Advanced satellite technology has been providing unique observations of global carbon dioxide (CO2) concentrations. These observations have revealed important CO2 variability at different timescales and over regional and planetary scales. Satellite CO2 retrievals have revealed that stratospheric sudden warming and the Madden-Julian Oscillation can modulate atmospheric CO2 concentrations in the mid-troposphere. Atmospheric CO2 also demonstrates variability at interannual timescales. In the tropical region, the El Niño–Southern Oscillation and the Tropospheric Biennial Oscillation can change atmospheric CO2 concentrations. At high latitudes, mid-tropospheric CO2 concentrations can be influenced by the Northern Hemispheric annular mode. In addition to modulations by the large-scale circulations, sporadic events such as wildfires, volcanic eruptions, and droughts, which change CO2 surface emissions, can cause atmospheric CO2 concentrations to increase significantly. The natural variability of CO2 summarized in this review can help us better understand its sources and sinks and its redistribution by atmospheric motion. ▪ Global satellite CO2 data offer a unique opportunity to explore CO2 variability in different regions. ▪ Atmospheric CO2 concentration demonstrates variations at intraseasonal, seasonal, and interannual timescales. ▪ Both large-scale circulations and variations of surface emissions can modulate CO2 concentrations in the atmosphere.

    更新日期:2019-12-31
  • Permeability of Clays and Shales
    Annu. Rev. Earth Planet. Sci. (IF 9.235) Pub Date : 2019-05-30
    C.E. Neuzil

    The low permeability of clays, shales, and other argillaceous lithologies makes them key controls of transport and deformation processes in the crust but is known for being challenging to characterize. As muds are modified by compaction and diagenesis to low-porosity shales, permeability can decrease by six or more orders of magnitude, but at large scales it is often dramatically and unpredictably increased by fractures, faults, and other features. Testing and inverse modeling show that petrophysical properties and the geological environment are dominant controls of clay and shale matrix permeability and its scale dependence. Active sedimentation and tectonism on continental margins cause large-scale permeability to vary with time, but in stable continent interiors it is unclear how regional permeability of argillaceous formations changes over time or, in most cases, what controls it. Although rarely considered, it is also unknown whether Darcian permeability adequately describes flow in clay-rich materials. ▪ Critical for problems in energy, water supply, waste isolation, and geologic hazards, clay and shale permeability remains problematic. ▪ Test data and inverse model analyses are beginning to reveal where and how permeability of clay and shale changes with scale. ▪ In clays and shales, causes of permeability scale effects, their time dependence, and even flow behavior continue to raise questions.

    更新日期:2019-12-31
  • Flood Basalts and Mass Extinctions
    Annu. Rev. Earth Planet. Sci. (IF 9.235) Pub Date : 2019-05-30
    Matthew E. Clapham; Paul R. Renne

    Flood basalts were Earth's largest volcanic episodes that, along with related intrusions, were often emplaced rapidly and coincided with environmental disruption: oceanic anoxic events, hyperthermals, and mass extinction events. Volatile emissions, both from magmatic degassing and vaporized from surrounding rock, triggered short-term cooling and longer-term warming, ocean acidification, and deoxygenation. The magnitude of biological extinction varied considerably, from small events affecting only select groups to the largest extinction of the Phanerozoic, with less-active organisms and those with less-developed respiratory physiology faring especially poorly. The disparate environmental and biological outcomes of different flood basalt events may at first order be explained by variations in the rate of volatile release modulated by longer trends in ocean carbon cycle buffering and the composition of marine ecosystems. Assessing volatile release, environmental change, and biological extinction at finer temporal resolution should be a top priority to refine ancient hyperthermals as analogs for anthropogenic climate change. ▪ Flood basalts, the largest volcanic events in Earth history, triggered dramatic environmental changes on land and in the oceans. ▪ Rapid volcanic carbon emissions led to ocean warming, acidification, and deoxygenation that often caused widespread animal extinctions. ▪ Animal physiology played a key role in survival during flood basalt extinctions, with reef builders such as corals being especially vulnerable. ▪ The rate and duration of volcanic carbon emission controlled the type of environmental disruption and the severity of biological extinction.

    更新日期:2019-12-31
  • Repeating Earthquakes
    Annu. Rev. Earth Planet. Sci. (IF 9.235) Pub Date : 2019-05-30
    Naoki Uchida; Roland Bürgmann

    Repeating earthquakes, or repeaters, are identical in location and geometry but occur at different times. They appear to represent recurring seismic energy release from distinct structures such as slip on a fault patch. Repeaters are most commonly found on creeping plate boundary faults, where seismic patches are loaded by surrounding slow slip, and they can be used to track fault creep at depth. Their hosting environments also include volcanoes, subducted slabs, mining-induced fault structures, glaciers, and landslides. While true repeaters should have identical seismic waveforms, small differences in their seismograms can be used to examine subtle changes in source properties or in material properties of the rocks through which the waves propagate. Source studies have documented the presence of smaller slip patches within the rupture areas of larger repeaters, illuminated earthquake triggering mechanisms, and revealed systematic changes in rupture characteristics as a function of loading rate. ▪ Repeating earthquakes are observed in diverse tectonic and nontectonic settings. ▪ Their occurrence patterns provide quantitative information about fault creep, earthquake cycle dynamics, triggering, and predictability. ▪ Their seismic waveform characteristics provide important insights on earthquake source variability and temporal Earth structure changes.

    更新日期:2019-12-31
  • Soil Functions: Connecting Earth's Critical Zone
    Annu. Rev. Earth Planet. Sci. (IF 9.235) Pub Date : 2019-05-30
    Steven A. Banwart; Nikolaos P. Nikolaidis; Yong-Guan Zhu; Caroline L. Peacock; Donald L. Sparks

    Soil is the central interface of Earth's critical zone—the planetary surface layer extending from unaltered bedrock to the vegetation canopy—and is under intense pressure from human demand for biomass, water, and food resources. Soil functions are flows and transformations of mass, energy, and genetic information that connect soil to the wider critical zone, transmitting the impacts of human activity at the land surface and providing a control point for beneficial human intervention. Soil functions are manifest during bedrock weathering and, in fully developed soil profiles, correlate with the porosity architecture of soil structure and arise from the development of soil aggregates as fundamental ecological units. Advances in knowledge on the mechanistic processes of soil functions, their connection throughout the critical zone, and their quantitative representation in mathematical and computational models define research frontiers that address the major global challenges of critical zone resource provisioning for human benefit. ▪ Connecting the mechanisms of soil functions with critical zone processes defines integrating science to tackle challenges of climate change and food and water supply. ▪ Soil functions, which develop through formation of soil aggregates as fundamental eco-logical units, are manifest at the earliest stages of critical zone evolution. ▪ Global degradation of soil functions during the Anthropocene is reversible through positive human intervention in soil as a central control point in Earth's critical zone. ▪ Measurement and mathematical translation of soil functions and critical zone processes offer new computational approaches for basic and applied geosciences research.

    更新日期:2019-12-31
  • Earthquake Early Warning: Advances, Scientific Challenges, and Societal Needs
    Annu. Rev. Earth Planet. Sci. (IF 9.235) Pub Date : 2019-05-30
    Richard M. Allen; Diego Melgar

    Earthquake early warning (EEW) is the delivery of ground shaking alerts or warnings. It is distinguished from earthquake prediction in that the earthquake has nucleated to provide detectable ground motion when an EEW is issued. Here we review progress in the field in the last 10 years. We begin with EEW users, synthesizing what we now know about who uses EEW and what information they need and can digest. We summarize the approaches to EEW and gather information about currently existing EEW systems implemented in various countries while providing the context and stimulus for their creation and development. We survey important advances in methods, instrumentation, and algorithms that improve the quality and timeliness of EEW alerts. We also discuss the development of new, potentially transformative ideas and methodologies that could change how we provide alerts in the future. ▪ Earthquake early warning (EEW) is the rapid detection and characterization of earthquakes and delivery of an alert so that protective actions can be taken. ▪ EEW systems now provide public alerts in Mexico, Japan, South Korea, and Taiwan and alerts to select user groups in India, Turkey, Romania, and the United States. ▪ EEW methodologies fall into three categories, point source, finite fault, and ground motion models, and we review the advantages of each of these approaches. ▪ The wealth of information about EEW uses and user needs must be employed to focus future developments and improvements in EEW systems.

    更新日期:2019-12-31
  • Noble Gases: A Record of Earth's Evolution and Mantle Dynamics
    Annu. Rev. Earth Planet. Sci. (IF 9.235) Pub Date : 2019-05-30
    Sujoy Mukhopadhyay; Rita Parai

    Noble gases have played a key role in our understanding of the origin of Earth's volatiles, mantle structure, and long-term degassing of the mantle. Here we synthesize new insights into these topics gained from high-precision noble gas data. Our analysis reveals new constraints on the origin of the terrestrial atmosphere, the presence of nebular neon but chondritic krypton and xenon in the mantle, and a memory of multiple giant impacts during accretion. Furthermore, the reservoir supplying primordial noble gases to plumes appears to be distinct from the mid-ocean ridge basalt (MORB) reservoir since at least 4.45 Ga. While differences between the MORB mantle and plume mantle cannot be explained solely by recycling of atmospheric volatiles, injection and incorporation of atmospheric-derived noble gases into both mantle reservoirs occurred over Earth history. In the MORB mantle, the atmospheric-derived noble gases are observed to be heterogeneously distributed, reflecting inefficient mixing even within the vigorously convecting MORB mantle. ▪ Primordial noble gases in the atmosphere were largely derived from planetesimals delivered after the Moon-forming giant impact. ▪ Heterogeneities dating back to Earth's accretion are preserved in the present-day mantle. ▪ Mid-ocean ridge basalts and plume xenon isotopic ratios cannot be related by differential degassing or differential incorporation of recycled atmospheric volatiles. ▪ Differences in mid-ocean ridge basalts and plume radiogenic helium, neon, and argon ratios can be explained through the lens of differential long-term degassing.

    更新日期:2019-12-31
  • Supraglacial Streams and Rivers
    Annu. Rev. Earth Planet. Sci. (IF 9.235) Pub Date : 2019-05-30
    Lincoln H Pitcher; Laurence C. Smith

    Supraglacial meltwater channels that flow on the surfaces of glaciers, ice sheets, and ice shelves connect ice surface climatology with subglacial processes, ice dynamics, and eustatic sea level changes. Their important role in transferring water and heat across and into ice is currently absent from models of surface mass balance and runoff contributions to global sea level rise. Furthermore, relatively little is known about the genesis, evolution, hydrology, hydraulics, and morphology of supraglacial rivers, and a first synthesis and review of published research on these unusual features is lacking. To that end, we review their (a) known geographical distribution; (b) formation, morphology, and sediment transport processes; (c) hydrology and hydraulics; and (d) impact on ice sheet surface energy balance, heat exchange, basal conditions, and ice shelf stability. We conclude with a synthesis of key knowledge gaps and provide recommendations for future research. ▪ Supraglacial streams and rivers transfer water and heat on glaciers, connecting climate with subglacial hydrology, ice sliding, and global sea level. ▪ Ice surface melting may expand under a warming climate, darkening the ice surface and further increasing melt.

    更新日期:2019-12-31
  • Isotopes in the Water Cycle: Regional- to Global-Scale Patterns and Applications
    Annu. Rev. Earth Planet. Sci. (IF 9.235) Pub Date : 2019-05-30
    Gabriel J. Bowen; Zhongyin Cai; Richard P. Fiorella; Annie L. Putman

    Stable isotope ratios of hydrogen and oxygen have been applied to water cycle research for over 60 years. Over the past two decades, however, new data, data compilations, and quantitative methods have supported the application of isotopic data to address large-scale water cycle problems. Recent results have demonstrated the impact of climate variation on atmospheric water cycling, provided constraints on continental- to global-scale land-atmosphere water vapor fluxes, revealed biases in the sources of runoff in hydrological models, and illustrated regional patterns of water use and management by people. In the past decade, global isotopic observations have spurred new debate over the role of soils in the water cycle, with potential to impact both ecological and hydrological theory. Many components of the water cycle remain underrepresented in isotopic databases. Increasing accessibility of analyses and improved platforms for data sharing will refine and grow the breadth of these contributions in the future. ▪ Isotope ratios in water integrate information on hydrological processes over scales from cities to the globe. ▪ Tracing water with isotopes helps reveal the processes that govern variability in the water cycle and may govern future global changes. ▪ Improvements in instrumentation, data sharing, and quantitative analysis have advanced isotopic water cycle science over the past 20 years.

    更新日期:2019-12-31
  • Marsh Processes and Their Response to Climate Change and Sea-Level Rise
    Annu. Rev. Earth Planet. Sci. (IF 9.235) Pub Date : 2019-05-30
    Duncan M. FitzGerald; Zoe Hughes

    In addition to their being vital components of mid- to high-latitude coastal ecosystems, salt marshes contain 0.1% of global sequestered terrestrial carbon. Their sustainability is now threatened by accelerating sea-level rise (SLR) that has reached a rate that is many times greater than the rate at which they formed and evolved. Modeling studies have been instrumental in predicting how marsh systems will respond to greater frequencies and durations of tidal inundation and in quantifying thresholds when marshes will succumb and begin to disintegrate due to accelerating SLR. Over the short term, some researchers believe that biogeomorphic feedbacks will improve marsh survival through greater biomass productivity enhanced by warmer temperatures and higher carbon dioxide concentrations. Increased sedimentation rates are less likely due to lower-than-expected suspended sediment concentrations. The majority of marsh loss today is through wave-induced edge erosion that beneficially adds sediment to the system. Edge erosion is partly offset by upland marsh migration during SLR. ▪ Despite positive biogeomorphic feedbacks, many salt marshes will succumb to accelerating sea-level rise due to insufficient mineral sediment. ▪ The latest multivariate marsh modeling is producing predictions of marsh evolution under various sea-level rise scenarios. ▪ The least well-known variables in projecting changes to salt marshes are suspended sediment concentrations and net sediment influx to the marsh. ▪ We are in the infancy of understanding the importance and processes of marsh edge erosion and the overall dynamicism of marshes. ▪ This review defines the latest breakthroughs in understanding the response of salt marshes to accelerating sea-level rise and decreasing sediment supply. ▪ Climate change is accelerating sea-level rise, warming temperatures, and increasing carbon dioxide, all of which are impacting marsh vegetation and vertical accretion.

    更新日期:2019-12-31
  • The Mesozoic Biogeographic History of Gondwanan Terrestrial Vertebrates: Insights from Madagascar's Fossil Record
    Annu. Rev. Earth Planet. Sci. (IF 9.235) Pub Date : 2019-05-30
    David W. Krause; Joseph J.W. Sertich; Patrick M. O'Connor; Kristina Curry Rogers; Raymond R. Rogers

    The Mesozoic plate tectonic and paleogeographic history of Gondwana had a profound effect on the distribution of terrestrial vertebrates. As the supercontinent fragmented into a series of large landmasses (South America, Africa-Arabia, Antarctica, Australia, New Zealand, the Indian subcontinent, and Madagascar), particularly during the Late Jurassic and Cretaceous, its terrestrial vertebrates became progressively isolated, evolving into unique faunal assemblages. We focus on four clades that, during the Mesozoic, had relatively low ability for dispersal across oceanic barriers—crocodyliforms, sauropod dinosaurs, nonavian theropod dinosaurs, and mammals. Their distributions reveal patterns that are critically important in evaluating various biogeographic hypotheses, several of which have been informed by recent discoveries from the Late Cretaceous of Madagascar. We also examine the effects of lingering, intermittent connections, or reconnections, of Gondwanan landmasses with Laurasia (through the Caribbean, Mediterranean, and Himalayan regions) on the distributions of different clades. ▪ This article reviews the biogeographic history of terrestrial vertebrates from the Mesozoic of the southern supercontinent Gondwana. ▪ Relatively large, terrestrial animals—including crocodyliforms, sauropod and nonavian theropod dinosaurs, and mammals—are the focus of this review. ▪ Most patterns related to vicariance occurred during the Late Jurassic and Cretaceous, the intervals of most active Gondwanan fragmentation. ▪ Recent discoveries of vertebrates from the Late Cretaceous of Madagascar have played a key role in formulating and testing various biogeographic hypotheses.

    更新日期:2019-12-31
  • Droughts, Wildfires, and Forest Carbon Cycling: A Pantropical Synthesis
    Annu. Rev. Earth Planet. Sci. (IF 9.235) Pub Date : 2019-05-30
    Paulo M. Brando; Lucas Paolucci; Caroline C. Ummenhofer; Elsa M. Ordway; Henrik Hartmann; Megan E. Cattau; Ludmila Rattis; Vincent Medjibe; Michael T. Coe; Jennifer Balch

    Tropical woody plants store ∼230 petagrams of carbon (PgC) in their aboveground living biomass. This review suggests that these stocks are currently growing in primary forests at rates that have decreased in recent decades. Droughts are an important mechanism in reducing forest C uptake and stocks by decreasing photosynthesis, elevating tree mortality, increasing autotrophic respiration, and promoting wildfires. Tropical forests were a C source to the atmosphere during the 2015–2016 El Niño–related drought, with some estimates suggesting that up to 2.3 PgC were released. With continued climate change, the intensity and frequency of droughts and fires will likely increase. It is unclear at what point the impacts of severe, repeated disturbances by drought and fires could exceed tropical forests’ capacity to recover. Although specific threshold conditions beyond which ecosystem properties could lead to alternative stable states are largely unknown, the growing body of scientific evidence points to such threshold conditions becoming more likely as climate and land use change across the tropics. ▪ Droughts have reduced forest carbon uptake and stocks by elevating tree mortality, increasing autotrophic respiration, and promoting wildfires. ▪ Threshold conditions beyond which tropical forests are pushed into alternative stable states are becoming more likely as effects of droughts intensify.

    更新日期:2019-12-31
  • Exoplanet Clouds
    Annu. Rev. Earth Planet. Sci. (IF 9.235) Pub Date : 2019-05-30
    Christiane Helling

    Clouds, which are common features in Earth's atmosphere, form in atmospheres of planets that orbit other stars than our Sun, in so-called extrasolar planets or exoplanets. Exoplanet atmospheres can be chemically extremely rich. Exoplanet clouds are therefore composed of a mix of materials that changes throughout the atmosphere. They affect atmospheres through element depletion and through absorption and scattering; hence, they have a profound impact on an atmosphere's energy budget. While astronomical observations point us to the presence of extrasolar clouds and make first suggestions on particle size and material composition, we require fundamental and complex modeling work to merge the individual observations into a coherent picture. Part of this work includes developing an understanding of cloud formation in nonterrestrial environments. ▪ Exoplanet atmospheres exhibit a wide chemical diversity that enables the formation of mineral clouds in contrast to the predominant water clouds on Earth. ▪ Clouds consume elements, causing specific atoms and molecules to drop in abundance. Transport processes such as gravitational settling or advection delocalize this process. ▪ Extrasolar planets can have extreme weather conditions where day- and nightside temperatures vary hugely. This affects cloud formation, and hence the cloud coverage and atmosphere's appearance can change dramatically. ▪ Dynamic extrasolar clouds develop intracloud lightning, and electric circuits may occur on more local, smaller scales in giant exoplanets compared to smaller, Earth-like planets with less dramatic hydrodynamics.

    更新日期:2019-12-31
  • The origin and early evolution of life on Earth.
    Annu. Rev. Earth Planet. Sci. (IF 9.235) Pub Date : 1990-01-01
    J Oró,S L Miller,A Lazcano

    We do not have a detailed knowledge of the processes that led to the appearance of life on Earth. In this review we bring together some of the most important results that have provided insights into the cosmic and primitive Earth environments, particularly those environments in which life is thought to have originated. To do so, we first discuss the evidence bearing on the antiquity of life on our planet and the prebiotic significance of organic compounds found in interstellar clouds and in primitive solar system bodies such as comets, dark asteroids, and carbonaceous chondrites. This is followed by a discussion on the environmental models of the Hadean and early Archean Earth, as well as on the prebiotic formation of organic monomers and polymers essential to life. We then consider the processes that may have led to the appearance in the Archean of the first cells, and how these processes may have affected the early steps of biological evolution. Finally, the significance of these results to the study of the distribution of life in the Universe is discussed.

    更新日期:2019-11-01
  • Understanding oblique impacts from experiments, observations, and modeling.
    Annu. Rev. Earth Planet. Sci. (IF 9.235) Pub Date : 2001-10-05
    E Pierazzo,H J Melosh

    Natural impacts in which the projectile strikes the target vertically are virtually nonexistent. Nevertheless, our inherent drive to simplify nature often causes us to suppose most impacts are nearly vertical. Recent theoretical, observational, and experimental work is improving this situation, but even with the current wealth of studies on impact cratering, the effect of impact angle on the final crater is not well understood. Although craters' rims may appear circular down to low impact angles, the distribution of ejecta around the crater is more sensitive to the angle of impact and currently serves as the best guide to obliquity of impacts. Experimental studies established that crater dimensions depend only on the vertical component of the impact velocity. The shock wave generated by the impact weakens with decreasing impact angle. As a result, melting and vaporization depend on impact angle; however, these processes do not seem to depend on the vertical component of the velocity alone. Finally, obliquity influences the fate of the projectile: in particular, the amount and velocity of ricochet are a strong function of impact angle.

    更新日期:2019-11-01
  • Stromatolites in Precambrian carbonates: evolutionary mileposts or environmental dipsticks?
    Annu. Rev. Earth Planet. Sci. (IF 9.235) Pub Date : 2001-09-07
    J P Grotzinger,A H Knoll

    Stromatolites are attached, lithified sedimentary growth structures, accretionary away from a point or limited surface of initiation. Though the accretion process is commonly regarded to result from the sediment trapping or precipitation-inducing activities of microbial mats, little evidence of this process is preserved in most Precambrian stromatolites. The successful study and interpretation of stromatolites requires a process-based approach, oriented toward deconvolving the replacement textures of ancient stromatolites. The effects of diagenetic recrystallization first must be accounted for, followed by analysis of lamination textures and deduction of possible accretion mechanisms. Accretion hypotheses can be tested using numerical simulations based on modem stromatolite growth processes. Application of this approach has shown that stromatolites were originally formed largely through in situ precipitation of laminae during Archean and older Proterozoic times, but that younger Proterozoic stromatolites grew largely through the accretion of carbonate sediments, most likely through the physical process of microbial trapping and binding. This trend most likely reflects long-term evolution of the earth's environment rather than microbial communities.

    更新日期:2019-11-01
  • Sediment bacteria: who's there, what are they doing, and what's new?
    Annu. Rev. Earth Planet. Sci. (IF 9.235) Pub Date : 1997-01-01
    K H Nealson

    The prokaryotes (bacteria) comprise the bulk of the biomass and chemical activity in sediments. They are well suited to their role as sediment chemists, as they are the right size and have the required metabolic versatility to oxidize the organic carbon in a variety of different ways. The characteristic vertical nutrient (electron donor and electron acceptor) profiles seen in sediments are produced as a result of microbial activities, with each nutrient a product or reactant of one or more metabolic groups. Thus, understanding the mechanisms by which the chemical environment of a sediment is generated and stabilized requires a knowledge of resident populations, something that has been very difficult to obtain, given the techniques available to microbiologists. however, the new approaches of molecular biology, which have added insights into the phylogenetic relationships of the prokaryotes, have also provided tools whereby sedimentary populations can be examined without the need for culturing the organisms. These techniques, in concert with new methods of microscopy, isolation of new metabolic groups, and the study of new ecosystems, suggest that there is much that will be learned about the microbiology of sedimentary environments in the coming years.

    更新日期:2019-11-01
  • The origin of life in the solar system: current issues.
    Annu. Rev. Earth Planet. Sci. (IF 9.235) Pub Date : 1995-01-01
    C F Chyba,G D McDonald

    The authors review current issues in the study of biogenesis and exobiology research. Topics include definitions of life; exobiological environments in the solar system, including the planets and their satellites, comets, and asteroids; energy sources for prebiotic chemistry, and the concept of the RNA world.

    更新日期:2019-11-01
  • Earth Abides Arsenic Biotransformations.
    Annu. Rev. Earth Planet. Sci. (IF 9.235) Pub Date : 2014-05-01
    Yong-Guan Zhu,Masafumi Yoshinaga,Fang-Jie Zhao,Barry P Rosen

    Arsenic is the most prevalent environmental toxic element and causes health problems throughout the world. The toxicity, mobility, and fate of arsenic in the environment are largely determined by its speciation, and arsenic speciation changes are driven, at least to some extent, by biological processes. In this article, biotransformation of arsenic is reviewed from the perspective of the formation of Earth and the evolution of life, and the connection between arsenic geochemistry and biology is described. The article provides a comprehensive overview of molecular mechanisms of arsenic redox and methylation cycles as well as other arsenic biotransformations. It also discusses the implications of arsenic biotransformation in environmental remediation and food safety, with particular emphasis on groundwater arsenic contamination and arsenic accumulation in rice.

    更新日期:2019-11-01
  • Autogenic Sedimentation in Clastic Stratigraphy
    Annu. Rev. Earth Planet. Sci. (IF 9.235) Pub Date : 2017-09-07
    Elizabeth A. Hajek, Kyle M. Straub

    Internally generated, or autogenic, terrestrial and marine sediment-transport dynamics can produce depositional patterns similar to those associated with climatic, tectonic, or sea level changes. A central challenge in accurately interpreting the sedimentary archive is determining what scales and types of deposits reflect autogenic controls on sedimentation in different environments. Autogenic sediment-transport dynamics commonly result from intermittent sediment storage in transient landforms, which produces episodic, spatially discontinuous sedimentation across a basin. The transition from localized, variable sedimentation to even, basin-wide sedimentation marks the shift from stochastic landscape dynamics to deterministic deposition responding to the long-term balance between sediment supply and the creation of space to accommodate sediment. This threshold can be measured in a wide variety of stratigraphic successions and has important bearing on whether climatic, tectonic, or sea level signals can be recognized in physical sedimentary deposits.

    更新日期:2017-09-21
  • Reconstructing Climate from Glaciers
    Annu. Rev. Earth Planet. Sci. (IF 9.235) Pub Date : 2017-09-07
    Andrew N. Mackintosh, Brian M. Anderson, Raymond T. Pierrehumbert

    Glaciers offer the potential to reconstruct past climate over timescales from decades to millennia. They are found on nearly every continent, and at the Last Glacial Maximum, glaciers were larger in all regions on Earth. The physics of glacier-climate interaction are relatively well understood, and glacier models can be used to reconstruct past climate from geological evidence of past glacier extent. This can lead to significant insights regarding past, present, and future climate. For example, glacier modeling has demonstrated that the near-ubiquitous global pattern of glacier retreat during the last few centuries resulted from a global-scale climate warming of ∼1°C, consistent with instrumental data and climate proxy records. Climate reconstructions from glaciers have also demonstrated that the tropics were colder at the Last Glacial Maximum than was originally inferred from sea surface temperature reconstructions. Future efforts to reconstruct climate from glaciers may provide new constraints on climate sensitivity to CO2 forcing, polar amplification of climate change, and more.

    更新日期:2017-09-21
  • The Late Heavy Bombardment
    Annu. Rev. Earth Planet. Sci. (IF 9.235) Pub Date : 2017-09-07
    William F. Bottke, Marc D. Norman

    Heavily cratered surfaces on the Moon, Mars, and Mercury show that the terrestrial planets were battered by an intense bombardment during their first billion years or more, but the timing, sources, and dynamical implications of these impacts are controversial. The Late Heavy Bombardment refers to impact events that occurred after stabilization of the planetary lithospheres such that they could be preserved as craters and basins. Lunar melt rocks and meteorite shock ages point toward a discrete episode of elevated impact flux between ∼3.5 and ∼4.0–4.2 Ga, and a relative quiescence between ∼4.0–4.2 and ∼4.4 Ga. Evidence from Precambrian impact spherule layers suggests that a long-lived tail of terrestrial impactors lasted to ∼2.0–2.5 Ga. Dynamical models that include populations residual from primary accretion and destabilized by giant planet migration can potentially account for the available observations, although all have pros and cons. The most parsimonious solution to match constraints is a hybrid model with discrete early, post-accretion and later, planetary instability–driven populations of impactors.

    更新日期:2017-09-21
  • The Rise of Animals in a Changing Environment: Global Ecological Innovation in the Late Ediacaran
    Annu. Rev. Earth Planet. Sci. (IF 9.235) Pub Date : 2017-09-07
    Mary L. Droser, Lidya G. Tarhan, James G. Gehling

    The evolutionary trajectory of early complex life on Earth is interpreted largely from the fossils of the Precambrian soft-bodied Ediacara Biota, which appeared and evolved during a time of dynamic biogeochemical and environmental fluctuation in the global ocean. The Ediacara Biota is historically divided into three successive Assemblages—the Avalon, the White Sea, and the Nama—which are marked by the appearance of novel biological traits and ecological strategies. In particular, the younger White Sea and Nama Assemblages record a “second wave” of ecological innovations, which included not only the development of uniquely Ediacaran body plans and ecologies, such as matground adaptations, but also the dual emergence of bilaterian-grade animals and Phanerozoic-style ecological innovations, including spatial heterogeneity, complex reproductive strategies, ecospace utilization, motility, and substrate competition. The late Ediacaran was an evolutionarily dynamic time characterized by strong environmental control over the distribution of taxa in time and space.

    更新日期:2017-09-21
  • Climate and the Pace of Erosional Landscape Evolution
    Annu. Rev. Earth Planet. Sci. (IF 9.235) Pub Date : 2017-09-07
    J. Taylor Perron

    Earth's climate affects nearly all aspects of landscape evolution, from the breakdown of rock to the delivery of sediment to the oceans. Yet quantifying climate's influence on landscapes is a major challenge, not only because it is difficult to know how landscapes responded to past changes in climate, but also because landscapes are shaped by various processes that respond to climate in different ways. I review the current state of efforts to quantify climate's effects on the rates of the main processes that drive landscape evolution, with a focus on unglaciated landscapes formed by bedrock erosion. Although many uncertainties remain, recent research has clarified how the processes governing hillslopes, bedrock channels, and chemical erosion depend on major climate factors such as precipitation and temperature. A few themes emerge, including the importance of climatically mediated biological processes, the role of variability, and the value of natural experiments for revealing climate's effects.

    更新日期:2017-09-21
  • Tectonic Evolution of the Central Andean Plateau and Implications for the Growth of Plateaus
    Annu. Rev. Earth Planet. Sci. (IF 9.235) Pub Date : 2017-09-07
    Carmala N. Garzione, Nadine McQuarrie, Nicholas D. Perez, Todd A. Ehlers, Susan L. Beck, Nandini Kar, Nathan Eichelberger, Alan D. Chapman, Kevin M. Ward, Mihai N. Ducea, Richard O. Lease, Christopher J. Poulsen, Lara S. Wagner, Joel E. Saylor, George Zandt, Brian K. Horton

    Current end-member models for the geodynamic evolution of orogenic plateaus predict (a) slow and steady rise during crustal shortening and ablative subduction (i.e., continuous removal) of the lower lithosphere or (b) rapid surface uplift following shortening, which is associated with punctuated removal of dense lower lithosphere and/or lower crustal flow. This review integrates results from recent studies of the modern lithospheric structure, geologic evolution, and surface uplift history of the Central Andean Plateau to evaluate the geodynamic processes involved in forming it. Comparison of the timing, magnitude, and distribution of shortening and surface uplift, in combination with other geologic evidence, highlights the pulsed nature of plateau growth. We discuss specific regions and time periods that show evidence for end-member geodynamic processes, including middle–late Miocene surface uplift of the southern Eastern Cordillera and Altiplano associated with shortening and ablative subduction, latest Oligocene–early Miocene and late Miocene–early Pliocene punctuated removal of dense lower lithosphere in the Eastern Cordillera and Altiplano, and late Miocene–early Pliocene crustal flow in the central and northern Altiplano.

    更新日期:2017-09-21
  • Statistics of Earthquake Activity: Models and Methods for Earthquake Predictability Studies
    Annu. Rev. Earth Planet. Sci. (IF 9.235) Pub Date : 2017-09-07
    Yosihiko Ogata

    Statistical methods and various models in time-space-magnitude parameter space of earthquakes are being developed to analyze seismic activity based on earthquake hypocenter catalogs that are routinely accumulated. Considering complex geophysical environments and uncertainties, we seek proper stochastic modeling that depends on the history of earthquake occurrences and relevant geophysical information for describing and forecasting earthquake activity. Also, we need empirical Bayesian models with many parameters in order to describe nonstationary or nonhomogeneous seismic activity. This review is concerned with earthquake predictability research aimed at realizing practical operational forecasting. In particular, uncertainty lies in identifying whether abnormal phenomena are precursors to large earthquakes. The predictability of such models can be examined by certain statistical criteria.

    更新日期:2017-09-21
  • Origin and Evolution of Regional Biotas: A Deep-Time Perspective
    Annu. Rev. Earth Planet. Sci. (IF 9.235) Pub Date : 2017-09-07
    Mark E. Patzkowsky

    Historical processes tens to hundreds of millions of years in the past have shaped not only the trajectory of life through time but also the distribution and composition of life today. Studies aimed at the origin and evolution of regional biotas promise to forge a stronger link among paleobiology, ecology, and evolutionary biology. Improvements in high-resolution stratigraphic interpretation, numerical modeling of the fossil record, and the application of phylogenetic methods to extinct groups will lead to advances in understanding of (a) assembly of regional biotas, (b) the ecology of extinct taxa, (c) the diversification and environmental expansion of major groups, (d) the processes underlying regional ecosystem persistence and pulsed change, and (e) whether or not diversity has limits over geologic time.

    更新日期:2017-09-21
  • Effects of Partial Melting on Seismic Velocity and Attenuation: A New Insight from Experiments
    Annu. Rev. Earth Planet. Sci. (IF 9.235) Pub Date : 2017-09-07
    Yasuko Takei

    The effects of partial melting on seismic velocity and attenuation have long been studied by focusing on the direct effects of melt, such as the poroelastic effect. The direct effects are generally very small for a very small melt fraction. Because geochemical studies have shown that the melt fraction during partial melting is very small (∼0.1%), it is difficult to explain upper-mantle low-velocity regions by the direct effects of melt. Recent experimental studies, by using a rock analog, have captured a significant enhancement of polycrystal anelasticity just before partial melting in the absence of melt. This newly recognized effect enables us to interpret seismological and geochemical observations consistently. The new anelasticity model significantly changes the interpretation of upper-mantle seismic structures. This review summarizes the recent progress in the understanding of polycrystal anelasticity, starting from a basic knowledge of linear anelasticity.

    更新日期:2017-09-21
  • Shape, Internal Structure, Zonal Winds, and Gravitational Field of Rapidly Rotating Jupiter-Like Planets
    Annu. Rev. Earth Planet. Sci. (IF 9.235) Pub Date : 2017-09-07
    Keke Zhang, Dali Kong, Gerald Schubert

    High-precision gravitational measurements by orbiting spacecraft provide a means of probing the structures, fluid motions, and convective dynamos in the interiors of the rapidly rotating outer planets. Here, the classical theory of rotating homogeneous planets is briefly reviewed. Emphasis is placed on recent developments in theories and methods that relate internal structure and processes to their gravitational signatures. Whereas early theories usually treated the effects of interior density stratification and rotational distortion as perturbations to a spherical state, recent research is marked by a self-consistent perturbation approach in which the leading-order problem accounts exactly for rotational distortion, thereby determining the basic shape, internal structure, and gravitational field of the planet. The next-order problem, which is mathematically and physically coupled with the leading-order problem, describes the modifications caused by internal fluid motions. Although the theories and methods have general applicability, advances have been spurred by the need to have a basis for interpretation of the gravitational data for Jupiter and Saturn expected from the Juno and Cassini missions.

    更新日期:2017-09-21
  • Tungsten Isotopes in Planets
    Annu. Rev. Earth Planet. Sci. (IF 9.235) Pub Date : 2017-09-07
    Thorsten Kleine, Richard J. Walker

    The short-lived Hf-W isotope system has a wide range of important applications in cosmochemistry and geochemistry. The siderophile behavior of W, combined with the lithophile nature of Hf, makes the system uniquely useful as a chronometer of planetary accretion and differentiation. Tungsten isotopic data for meteorites show that the parent bodies of some differentiated meteorites accreted within 1 million years after Solar System formation. Melting and differentiation on these bodies took ∼1–3 million years and was fueled by decay of 26Al. The timescale for accretion and core formation increases with planetary mass and is ∼10 million years for Mars and >34 million years for Earth. The nearly identical 182W compositions for the mantles of the Moon and Earth are difficult to explain in current models for the formation of the Moon. Terrestrial samples with ages spanning ∼4 billion years reveal small 182W variations within the silicate Earth, demonstrating that traces of Earth's earliest formative period have been preserved throughout Earth's history.

    更新日期:2017-09-21
  • Forming Planets via Pebble Accretion
    Annu. Rev. Earth Planet. Sci. (IF 9.235) Pub Date : 2017-09-07
    Anders Johansen, Michiel Lambrechts

    The detection and characterization of large populations of pebbles in protoplanetary disks have motivated the study of pebble accretion as a driver of planetary growth. This review covers all aspects of planet formation by pebble accretion, from dust growth over planetesimal formation to the accretion of protoplanets and fully grown planets with gaseous envelopes. Pebbles are accreted at a very high rate—orders of magnitude higher than planetesimal accretion—and the rate decreases only slowly with distance from the central star. This allows planetary cores to start their growth in much more distant positions than their final orbits. The giant planets orbiting our Sun and other stars, including systems of wide-orbit exoplanets, can therefore be formed in complete consistency with planetary migration. We demonstrate how growth tracks of planetary mass versus semimajor axis can be obtained for all the major classes of planets by integrating a relatively simple set of governing equations.

    更新日期:2017-09-21
  • Southeast Asia: New Views of the Geology of the Malay Archipelago
    Annu. Rev. Earth Planet. Sci. (IF 9.235) Pub Date : 2017-09-07
    Robert Hall

    Southeast (SE) Asia is surrounded by subduction zones causing intense seismicity and volcanic activity. Subduction has been the principal tectonic driver of collisions that caused the growth of continental SE Asia, and most recently the collision of Australia with SE Asia. The western part of SE Asia, Sundaland, is a heterogeneous and weak region, reflecting processes that can be observed today in the east, where there are subduction zones in different stages of development. A close relationship between subduction rollback and extension has caused dramatic elevation of land, exhumation of deep crust, and spectacular subsidence of basins, observable with remotely acquired images and seismic and multibeam data obtained from oil exploration. New dating indicates that subsidence and uplift occurred at high rates during short time intervals. Laboratory studies, modeling, and reconstructions provide valuable insights, but field-based studies continue to present surprises and new discoveries essential for interpretations of the geological history of the region.

    更新日期:2017-09-21
  • Photochemistry of Sulfur Dioxide and the Origin of Mass-Independent Isotope Fractionation in Earth's Atmosphere
    Annu. Rev. Earth Planet. Sci. (IF 9.235) Pub Date : 2017-09-07
    Shuhei Ono

    Archean sulfide and sulfate minerals commonly exhibit anomalous ratios among four stable sulfur isotopes, 32S, 33S, 34S, and 36S. These anomalous relationships, referred to as sulfur mass-independent fractionation (S-MIF), provide strong evidence for an early anoxic atmosphere. Correlated variations among three isotope ratios (δ33S, δ34S, and δ36S) can be observed in rocks throughout the Archean and are a key clue toward identifying the source reaction of S-MIF. Studies to investigate the origin of Archean S-MIF so far have primarily focused on the photochemistry of sulfur dioxide (SO2). Photolysis of SO2 at wavelengths <220 nm and photoexcitation at 240–340 nm both yield large-magnitude S-MIF. Proposed mechanisms of S-MIF include isotopologue-dependent self-shielding, cross-sectional amplitudes, and vibronic coupling during intersystem crossing. This review discusses the emerging picture of the physical origins of S-MIF and their implications for the chemistry of the early Earth's atmosphere.

    更新日期:2017-09-21
  • Back-Projection Imaging of Earthquakes
    Annu. Rev. Earth Planet. Sci. (IF 9.235) Pub Date : 2017-09-07
    Eric Kiser, Miaki Ishii

    Back-projection analysis of earthquakes is a type of array processing that images the source of seismic waves coherently recorded at stations throughout the seismic network. The method was developed following the magnitude 9.2 Sumatra-Andaman earthquake in 2004. Although properties of earthquakes have been investigated using array data prior to the introduction of the back-projection method, this technique differs from other approaches because it makes limited assumptions and allows detailed and complex rupture propagation to be examined. These advantages have led several researchers to apply the method to many of the largest earthquakes to occur this century. The method has also been effective for the detection of smaller events. A critical component of the success of back-projection has been the development of large-scale, dense seismic arrays. Further improvements and future applications of the method will depend greatly on the continued maintenance and development of these networks.

    更新日期:2017-09-21
  • Interface Kinetics, Grain-Scale Deformation, and Polymorphism
    Annu. Rev. Earth Planet. Sci. (IF 9.235) Pub Date : 2017-09-07
    S.J.S. Morris

    Deviatoric stress generated within subducting slabs by the olivine–spinel transformation has been modeled by assuming the phases to be simply connected rather than comprising a mixture in which one phase is embedded within another. Here, we use a simplified model to explain how transformation strain is incorporated into a continuum model, and we then use the simplified model to explain quantitatively the origin of the unreasonably large deviatoric stresses predicted by existing slab models. We review experiments on the transformation of single-crystal samples and argue that they are consistent with the occurrence, at the grain scale, of deviatoric stresses comparable with those predicted (erroneously) to exist at the slab scale by those slab models. Using a simple example, we show that although large deviatoric stresses can exist at the grain scale, their average over a sample containing many grains can be hydrostatic. This leads us to the problem of modeling the microscale structure. We outline the thermodynamics needed for such nonhydrostatic systems, and we illustrate their use and implications with examples.

    更新日期:2017-09-21
  • Hydrogeomorphic Ecosystem Responses to Natural and Anthropogenic Changes in the Loess Plateau of China
    Annu. Rev. Earth Planet. Sci. (IF 9.235) Pub Date : 2017-09-07
    Bojie Fu, Shuai Wang, Yu Liu, Jianbo Liu, Wei Liang, Chiyuan Miao

    China's Loess Plateau is both the largest and deepest loess deposit in the world, and it has long been one of the most severely eroded areas on Earth. Since the 1970s, numerous soil- and water-conservation practices have been implemented: terracing, planting of vegetation, natural vegetation rehabilitation, and check-dam construction. With the implementation of the Grain-for-Green Project in 1999, the Loess Plateau has become the most successful ecological restoration zone in China. However, these large-scale restoration measures and drought have significantly reduced both runoff and sediment from the Loess Plateau. This situation has both advantages and disadvantages for the lower Yellow River. Some local soil erosion has been successfully controlled, but the whole regional ecosystem remains very fragile. Therefore, it is necessary to balance each ecosystem service, for example, by determining the region's vegetation capacity and its spatial distribution for the sustainable development of the socioecological system of the Loess Plateau.

    更新日期:2017-09-21
  • Aerosol Effects on Climate via Mixed-Phase and Ice Clouds
    Annu. Rev. Earth Planet. Sci. (IF 9.235) Pub Date : 2017-09-07
    T. Storelvmo

    Clouds in Earth's atmosphere can be composed of liquid droplets, ice crystals, or a combination of the two. Clouds’ thermodynamic phase is largely controlled by temperature, but other factors can also have a significant effect. Aerosols—i.e., particles suspended in Earth's atmosphere—affect cloud properties differently depending on cloud phase and can potentially have a strong influence on climate via any cloud type. Aerosol-cloud-climate interactions have been a topic of active research for more than two decades, but these interactions nevertheless currently represent one of the most uncertain forcings of climate change over the past century. Most research to date has focused on how aerosols can impact climate via liquid clouds, which are better understood and observed than their ice-containing counterparts. Thus, the problem of how liquid clouds mediate aerosols’ effects on climate is a more tractable one. However, there is no a priori reason to think that mixed-phase and ice clouds are any less affected by changes in atmospheric aerosol composition than liquid clouds, and estimates of how aerosols can influence these ice-containing clouds have started to emerge. Laboratory and field work, as well as satellite observations, is now shifting attention to this new frontier in the field of aerosol-cloud-climate interactions, allowing for improved representation of ice processes in numerical models. Here, we review this recent progress in our understanding of aerosol effects on mixed-phase and ice clouds, focusing on the four underpinning research pillars of laboratory experiments, field observations, satellite retrievals, and numerical modeling of global climate. Evident from this review is the possibility of a powerful yet poorly constrained climate forcing, which is uncertain in terms of both its magnitude and its sign.

    更新日期:2017-09-21
  • Earth's Continental Lithosphere Through Time
    Annu. Rev. Earth Planet. Sci. (IF 9.235) Pub Date : 2017-09-07
    Chris J. Hawkesworth, Peter A. Cawood, Bruno Dhuime, Tony I.S. Kemp

    The record of the continental lithosphere is patchy and incomplete; no known rock is older than 4.02 Ga, and less than 5% of the rocks preserved are older than 3 Ga. In addition, there is no recognizable mantle lithosphere from before 3 Ga. We infer that there was lithosphere before 3 Ga and that ∼3 Ga marks the stabilization of blocks of continental lithosphere that have since survived. This was linked to plate tectonics emerging as the dominant tectonic regime in response to thermal cooling, the development of a more rigid lithosphere, and the recycling of water, which may in turn have facilitated plate tectonics. A number of models, using different approaches, suggest that at 3 Ga the volume of continental crust was ∼70% of its present-day volume and that this may be a minimum value. The continental crust before 3 Ga was on average more mafic than that generated subsequently, and this pre-3 Ga mafic new crust had fractionated Lu/Hf and Sm/Nd ratios as inferred for the sources of tonalite-trondhjemite-granodiorite and later granites. The more intermediate composition of new crust generated since 3 Ga is indicated by its higher Rb/Sr ratios. This change in composition was associated with an increase in crustal thickness, which resulted in more emergent crust available for weathering and erosion. This in turn led to an increase in the Sr isotope ratios of seawater and in the drawdown of CO2. Since 3 Ga, the preserved record of the continental crust is marked by global cycles of peaks and troughs of U-Pb crystallization ages, with the peaks of ages appearing to match periods of supercontinent assembly. There is increasing evidence that the peaks of ages represent enhanced preservation of magmatic rocks in periods leading up to and including continental collision in the assembly of supercontinents. These are times of increased crustal growth because more of the crust that is generated is retained within the crust. The rates of generation of continental crust and mantle lithosphere may have remained relatively constant at least since 3 Ga, yet the rates of destruction of continental crust have changed with time. Only relatively small volumes of rock are preserved from before 3 Ga, and so it remains difficult to establish which of these are representative of global processes and the extent to which the rock record before 3 Ga is distorted by particular biases.

    更新日期:2017-09-21
  • Seismic and Electrical Signatures of the Lithosphere–Asthenosphere System of the Normal Oceanic Mantle
    Annu. Rev. Earth Planet. Sci. (IF 9.235) Pub Date : 2017-09-07
    Hitoshi Kawakatsu, Hisashi Utada

    Although plate tectonics started as a theory of the ocean basins nearly 50 years ago, the mechanical details of how it works are still poorly known. Our understanding of these details has been hampered partly by our inability to characterize the physical nature of the lithosphere–asthenosphere system (LAS) beneath the ocean. We review the existing observational constraints on the seismic and electrical properties of the LAS, particularly for normal oceanic regions away from mid-oceanic ridges, hot spots, and subduction zones, where plate tectonics is expected to present its simplest form. Whereas a growing volume of seismic data on land has provided remarkable advances in large-scale pictures, seafloor observations have been shedding new light on essential details. By combing through these observational constraints, researchers are unveiling the nature of the enigmatic LAS. Future directions for large-scale seafloor observations are also discussed.

    更新日期:2017-09-21
  • Major Questions in the Study of Primate Origins
    Annu. Rev. Earth Planet. Sci. (IF 9.235) Pub Date : 2017-09-07
    Mary T. Silcox, Sergi López-Torres

    Numerous factors have stimulated new enthusiasm for understanding the process of primate origins, including new fossil discoveries, improvements to methods for analyzing molecular data, and technological advances. These novel approaches have led to a better appreciation of the complexities of early primate evolution. Eight fundamental questions provide a framework for thinking about these issues. Among these topics are the phylogenetic position of Primates in Mammalia and the membership of particular fossil groups in the order. Also of central interest are questions about early primate ecology and anatomy such as the ancestral body mass, diet, locomotor mode, interactions with predators, and brain size and form. And finally, considerations of the paleontological record need to be informed by the most relevant living models, which help flesh out the story that is being told by fossils. Although much is known about all of these areas, fundamental questions still remain.

    更新日期:2017-09-21
  • Origin and Evolution of Water in the Moon's Interior
    Annu. Rev. Earth Planet. Sci. (IF 9.235) Pub Date : 2017-09-07
    Erik H. Hauri, Alberto E. Saal, Miki Nakajima, Mahesh Anand, Malcolm J. Rutherford, James A. Van Orman, Marion Le Voyer

    Nearly forty years after the return of the first lunar samples to Earth, improvements in laboratory detection limits made possible the first definitive discovery of magmatic water in lunar volcanic samples. The intervening decade has seen an exponential increase in the amount of data on the abundance of magmatic water, and its hydrogen isotope composition, in various rock types recovered from the Moon. Here we review these data and describe how the abundance of water in the lunar interior places important constraints on models for the high-temperature origin and evolution of the Moon.

    更新日期:2017-09-21
  • Plant Evolution and Climate Over Geological Timescales
    Annu. Rev. Earth Planet. Sci. (IF 9.235) Pub Date : 2017-09-07
    C. Kevin Boyce, Jung-Eun Lee

    The terrestrial vegetation is unambiguously an important factor in the climate system, modulating the exchange of energy, momentum, water vapor, and other trace gases between land and atmosphere. Here, we review the evolution of the terrestrial flora from the Proterozoic through to the Neogene at three distinct scales—the overall evolution of floral composition, the evolution of plant physiology, and the evolution of landscape occupation both spatially and seasonally—all in the context of how the vegetation may have influenced climate through time and which deep-time evolutionary transitions may have had the greatest effect. Our focus is upon the direct impacts of the vegetation on temperature and precipitation, but we also consider the indirect impacts of plants on climate via atmospheric composition. We argue that the times of greatest change in plant climate feedbacks are likely to have been the Carboniferous and the early Paleogene.

    更新日期:2017-09-21
  • The Fascinating and Complex Dynamics of Geyser Eruptions
    Annu. Rev. Earth Planet. Sci. (IF 9.235) Pub Date : 2017-09-07
    Shaul Hurwitz, Michael Manga

    Geysers episodically erupt liquid and vapor. Despite two centuries of scientific study, basic questions persist—why do geysers exist? What determines eruption intervals, durations, and heights? What initiates eruptions? Through monitoring eruption intervals, analyzing geophysical data, taking measurements within geyser conduits, performing numerical simulations, and constructing laboratory models, some of these questions have been addressed. Geysers are uncommon because they require a combination of abundant water recharge, magmatism, and rhyolite flows to supply heat and silica, and large fractures and cavities overlain by low-permeability materials to trap rising multiphase and multicomponent fluids. Eruptions are driven by the conversion of thermal to kinetic energy during decompression. Larger and deeper cavities permit larger eruptions and promote regularity by isolating water from weather variations. The ejection velocity may be limited by the speed of sound of the liquid + vapor mixture.

    更新日期:2017-09-21
  • Researching the Earth—and a Few of Its Neighbors
    Annu. Rev. Earth Planet. Sci. (IF 9.235) Pub Date : 2017-09-07
    Susan Werner Kieffer

    During my career, our knowledge of erupting geysers and volcanoes in the Solar System has exploded. In this prefatory, I tell how I became fascinated with high-speed processes through studying meteorite impact dynamics, and then how my initial idea of studying Old Faithful geyser as a volcanic analog led me to work not only on the dynamics of eruption of Mount St. Helens in 1980 but also on geysers erupting on Io (a fiery satellite of Jupiter), Triton (a frigid satellite of Neptune), and Enceladus (an active satellite of Saturn). Unforeseeably, the study of these events also led to work on mineral thermodynamics and the hydraulics and geomorphic evolution of rapids in the Grand Canyon. This is a narrative, not a formal review article, but the reader can find references in the Related Resources section to explore topics in more detail.

    更新日期:2017-09-21
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