Annual Review of Earth and Planetary Sciences
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Flood Basalts and Mass Extinctions 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.
Annual Review of Earth and Planetary Sciences - Tập 47 Số 1 - Trang 275-303 - 2019
THE MIDCONTINENT RIFT SYSTEM
Annual Review of Earth and Planetary Sciences - Tập 13 Số 1 - Trang 345-383 - 1985
The Thermal Conductivity of Earth's Core: A Key Geophysical Parameter's Constraints and Uncertainties The thermal conductivity of iron alloys at high pressures and temperatures is a critical parameter in governing ( a) the present-day heat flow out of Earth's core, ( b) the inferred age of Earth's inner core, and ( c) the thermal evolution of Earth's core and lowermost mantle. It is, however, one of the least well-constrained important geophysical parameters, with current estimates for end-member iron under core-mantle boundary conditions varying by about a factor of 6. Here, the current state of calculations, measurements, and inferences that constrain thermal conductivity at core conditions are reviewed. The applicability of the Wiedemann-Franz law, commonly used to convert electrical resistivity data to thermal conductivity data, is probed: Here, whether the constant of proportionality, the Lorenz number, is constant at extreme conditions is of vital importance. Electron-electron inelastic scattering and increases in Fermi-liquid-like behavior may cause uncertainties in thermal conductivities derived from both first-principles-associated calculations and electrical conductivity measurements. Additional uncertainties include the role of alloying constituents and local magnetic moments of iron in modulating the thermal conductivity. Thus, uncertainties in thermal conductivity remain pervasive, and hence a broad range of core heat flows and inner core ages appear to remain plausible.
Annual Review of Earth and Planetary Sciences - Tập 46 Số 1 - Trang 47-66 - 2018
REAL-TIME SEISMOLOGY AND EARTHQUAKE DAMAGE MITIGATION ▪ Abstract Real-time seismology refers to a practice in which seismic data are collected and analyzed quickly after a significant seismic event, so that the results can be effectively used for postearthquake emergency response and early warning. As the technology of seismic instrumentation, telemetry, computers, and data storage facility advances, the real-time seismology for rapid postearthquake notification is essentially established. Research for early warning is still underway. Two approaches are possible: (a) regional warning and (b) on-site (or site-specific) warning. In (a), the traditional seismological method is used to locate an earthquake, determine the magnitude, and estimate the ground motion at other sites. In (b), the beginning of the ground motion (mainly P wave) observed at a site is used to predict the ensuing ground motion at the same site. An effective approach to on-site warning is discussed in light of earthquake rupture physics.
Annual Review of Earth and Planetary Sciences - Tập 33 Số 1 - Trang 195-214 - 2005
The Early Origins of Terrestrial C<sub>4</sub> Photosynthesis 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, δ13 C 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 δ13 C proxy records indicate that the timing of C4 geographical expansion was not globally synchronous, and thus point toward more regional controls on the development of C4 -dominated ecosystems. Terrestrial and marine records indicate that continental aridity and wind strength increased during the Late Miocene. These conditions would have likely increased fire occurrence and fire intensity leading to the clearing of large tree stands and the expansion of C4 grasses in warm-season precipitation regimes.
Annual Review of Earth and Planetary Sciences - Tập 35 Số 1 - Trang 435-461 - 2007
Evolution of Grasses and Grassland Ecosystems The evolution and subsequent ecological expansion of grasses (Poaceae) since the Late Cretaceous have resulted in the establishment of one of Earth's dominant biomes, the temperate and tropical grasslands, at the expense of forests. In the past decades, several new approaches have been applied to the fossil record of grasses to elucidate the patterns and processes of this ecosystem transformation. The data indicate that the development of grassland ecosystems on most continents was a multistage process involving the Paleogene appearance of (C3 and C4 ) open-habitat grasses, the mid-late Cenozoic spread of C3 grass-dominated habitats, and, finally, the Late Neogene expansion of C4 grasses at tropical-subtropical latitudes. The evolution of herbivores adapted to grasslands did not necessarily coincide with the spread of open-habitat grasses. In addition, the timing of these evolutionary and ecological events varied between regions. Consequently, region-by-region investigations using both direct (plant fossils) and indirect (e.g., stable carbon isotopes, faunas) evidence are required for a full understanding of the tempo and mode of grass and grassland evolution.
Annual Review of Earth and Planetary Sciences - Tập 39 Số 1 - Trang 517-544 - 2011
Global Cooling by Grassland Soils of the Geological Past and Near Future Major innovations in the evolution of vegetation such as the Devonian origin of forests created new weathering regimes and soils (Alfisols, Histosols) that increased carbon consumption and sequestration and ushered in the Permian-Carboniferous Ice Age. Similarly, global expansion of grasslands and their newly evolved, carbon-rich soils (Mollisols) over the past 40 million years may have induced global cooling and ushered in Pleistocene glaciation. Grassland evolution has been considered a consequence of mountain uplift and tectonic reorganization of ocean currents, but it can also be viewed as a biological force for global change through coevolution of grasses and grazers. Organisms in such coevolutionary trajectories adapt to each other rather than to their environment, and so can be forces for global change. Some past farming practices have aided greenhouse gas release. However, modern grassland agroecosystems are a potential carbon sink already under intensive human management, and carbon farming techniques may be useful in curbing anthropogenic global warming.
Annual Review of Earth and Planetary Sciences - Tập 41 Số 1 - Trang 69-86 - 2013
HIGH-MG ANDESITES IN THE SETOUCHI VOLCANIC BELT, SOUTHWESTERN JAPAN: Analogy to Archean Magmatism and Continental Crust Formation? The occurrence of unusual high-Mg andesite (HMA) characterizes the Setouchi volcanic belt in SW Japan, which was activated at 13.7±1.0 Ma by subduction of the young and hot Shikoku Basin lithosphere into the high-temperature upper mantle. This tectonic setting may be analogous to the thermal regime during Archean times, which suggests more ubiquitous production of HMA. A plausible process that can comprehensively account for the petrological and geochemical characteristics of Setouchi HMAs involves partial melting of subducting lithosphere, subsequent melt-mantle interactions, and final equilibration with the upper-most mantle. HMAs and more differentiated andesites, which are coined sanukitoids, are distinct in that they are phenocryst-poor (<10%), compact, and nearly anhydrous, despite HMA magmas originally containing ∼7 wt% H2 O, and commonly form composite lava flows. One mechanism for explaining these features is formation of a mostly solidified HMA pluton, remelting of the HMA pluton by intrusion of a high-temperature basaltic magma, consequent production of a nearly dry HMA magma, and mixing of this HMA magma with overlying residual felsic melts during ascent to form a zoned magma reservoir.
Annual Review of Earth and Planetary Sciences - Tập 34 Số 1 - Trang 467-499 - 2006
Extratropical Cooling, Interhemispheric Thermal Gradients, and Tropical Climate Change Recent studies suggest the existence of a global atmospheric teleconnection of extratropical cooling to the tropical rainfall climate, mediated through the development of a thermal contrast between the hemispheres—an interhemispheric thermal gradient. This teleconnection has been largely motivated by studies that show a global synchronization of rapid climate change during abrupt climate changes of the last glacial period, in addition to attribution studies of twentieth-century Sahel drought and studies that examined the climate impacts of anthropogenic aerosols. This research has led to interesting developments in atmospheric dynamics of the underlying mechanisms and in applications toward understanding past and present tropical climate change. The emerging teleconnection hypothesis promises to offer new insights into understanding future patterns of tropical rainfall changes due to interhemispheric thermal gradients from greenhouse warming, aerosols, and land-use change.
Annual Review of Earth and Planetary Sciences - Tập 40 Số 1 - Trang 383-412 - 2012
The Carbon Budget in Soils ▪ Abstract The global soil C reservoir, ∼1500 Gt of C (1 Gt = 1012 kg of C), is dynamic on decadal time scales and is sensitive to climate and human disturbance. At present, as a result of land use, soil C is a source of atmospheric CO2 in the tropics and possibly part of a sink in northern latitudes. Here I review the processes responsible for maintaining the global soil C reservoir and what is known about how it responds to direct and indirect human perturbations. “I am fire and air; my other elements I give to baser life” —William Shakespeare, Antony and Cleopatra
Annual Review of Earth and Planetary Sciences - Tập 29 Số 1 - Trang 535-562 - 2001
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