Showing papers in "Annual Review of Earth and Planetary Sciences in 2006"
TL;DR: This paper measured the timing and rates at which rocks approach the surface and cool as a result of exhumation, and used thermochronology to constrain erosion rates and their spatial-temporal variations on timescales of ∼10 5 −10 7 years.
Abstract: Erosion of orogenic mountain ranges exhumes deeply buried rocks and controls weathering, climate, and sediment production and transport at a variety of scales. Erosion also affects the topographic form and kinematics of orogens, and it may provide dynamic feedbacks between climate and tectonics by spatially focused erosion and rock uplift. Thermochronology measures the timing and rates at which rocks approach the surface and cool as a result of exhumation. Relatively well-understood noble gas and fission-track thermochronometric systems have closure temperatures ranging from ∼60 to ∼550 ◦ C, making them sensitive to exhumation through crustal depths of about one to tens of kilometers. Thus, thermochronology can constrain erosion rates and their spatial-temporal variations on timescales of ∼10 5 –10 7 years, commensurate with orogenic growth and decay cycles and possible climate-tectonic feedback response times. Useful methods for estimating erosion rates include inverting ages for erosion rates using crustal thermal models, vertical transects, and detrital approaches. Spatial-temporal patterns of thermochronometrically determined erosion rates help constrain flow of material through orogenic wedges, orogenic growth and decay cycles, paleorelief, and relationships with structural, geomorphic, or climatic features.
823 citations
TL;DR: The Yarkovsky and YORP effects are thermal radiation forces and torques that cause small objects to undergo semimajor axis drift and spin vector modifications, respectively, as a function of their spin, orbit, and material properties as discussed by the authors.
Abstract: The Yarkovsky and YORP (Yarkovsky-O’Keefe-Radzievskii-Paddack) effects are thermal radiation forces and torques that cause small objects to undergo semimajor axis drift and spin vector modifications, respectively, as a function of their spin, orbit, and material properties. These mechanisms help to (a) deliver asteroids (and meteoroids) with diameter D < 40 km from their source locations in the main belt to chaotic resonance zones capable of transporting this material to Earth-crossing orbits; (b) disperse asteroid families, with drifting bodies jumping or becoming trapped in mean-motion and secular resonances within the main belt; (c) modify the rotation rates and obliquities of D < 40 km asteroids; and (d ) allow asteroids to enter into spin-orbit resonances, which affect the evolution of their spin vectors and feedback into the Yarkovsky-driven semimajor axis evolution. Accordingly, we suggest that nongravitational forces should now be considered as important as collisions and gravitational perturbations to our overall understanding of asteroid evolution.
661 citations
TL;DR: In this article, the authors studied the relationship between sediment transport and river morphology by defining sediment transport regimes on the basis of the Shields number, a non-dimensional measure of the capacity of the channel to move sediment of a given caliber.
Abstract: The morphology of an alluvial river channel is the consequence of sediment transport and sedimentation in the river. Morphological style is determined chiefly by the caliber and quantity of sediment delivered to the channel, although modulated by channel scale. Yet the relations between sediment transport and river morphology have received only limited, qualitative attention. In this review, the problem is studied by defining sediment transport regimes on the basis of the Shields number, a nondimensional measure of the capacity of the channel to move sediment of a given caliber. The problem is also approached from an inverse perspective by which the quantity and character of sediment deposits are used to infer details about the variation of sediment transport and sedimentation along a channel. Coupling the two approaches establishes a basis to gain new insights into the origins of alluvial channel morphology.
607 citations
TL;DR: Very low storage capacity in the lower mantle, if verified experimentally, presents a challenge to the view that the H2O-rich sources of oceanic island basalts reside in the upper mantle as mentioned in this paper.
Abstract: Hydrous melting driven by changes in H2O storage capacity may occur in a variety of settings in the mantle, including in oceanic basalt sources and in deeper regions above and below the transition zone. The 50–200 ppm H2O in the upper mantle likely derives from a blend of sources that may include residues of hydrous partial melting, either in the deep mantle and/or beneath arcs or oceanic islands. Relative to the large storage capacity in the transition zone, low storage capacities above and below may lead to hydrous melting for material upwelling through 410 km or downwelling through 670 km. The apparently very low storage capacity of the lower mantle (<20 ppm H2O) may force melting even if downwelling rocks have normal upper mantle H2O (50–200 ppm) concentrations. Very low storage capacity in the lower mantle, if verified experimentally, presents a challenge to the view that the H2O-rich sources of oceanic island basalts reside in the lower mantle.
536 citations
TL;DR: Several mechanisms have been proposed to explain triggering through changes in magma overpressure, including the growth of bubbles, the advection of large pressures by rising bubbles, and overturn of magma chambers as discussed by the authors.
Abstract: Approximately 0.4% of explosive volcanic eruptions occur within a few days of large, distant earthquakes. This many “triggered” eruptions is much greater than expected by chance. Several mechanisms have been proposed to explain triggering through changes in magma overpressure, including the growth of bubbles, the advection of large pressures by rising bubbles, and overturn of magma chambers. Alternatively, triggered eruptions may occur through failure of rocks surrounding stored magma. All these mechanisms require a process that enhances small static stress changes caused by earthquakes or that can convert (the larger) transient, dynamic strains into permanent changes in pressure. All proposed processes, in addition to viscoelastic relaxation of stresses, can result in delayed triggering of eruptions, although quantifying the connection between earthquakes and delayed, triggered eruptions is much more challenging. Mud volcanoes and geysers also respond to distant earthquakes. Mud volcanoes that discharge mud from depths greater than many hundreds of meters may be triggered by liquefaction caused by shaking, and may thus be similar to small mud volcanoes that originate within a few meters of the surface. Changes in permeability of the matrix surrounding main geyser conduits, by opening or creating new fractures, may explain the observed changes in their eruption frequency.
391 citations
TL;DR: The view of the atmospheric general circulation presented in this article focuses not on Earth's general circulation as such but on a continuum of idealized circulations with axisymmetric flow statistics, and the characteristics of the tropical Hadley circulation, of the extratropical circulation, and of atmospheric macroturbulence may depend on parameters such as the planet radius and rotation rate and the strength of the differential heating at the surface.
Abstract: Theories of how Earth’s surface climate may change in the future, of how it may have been in the past, and of how it is related to climates of other planets must build upon a theory of the general circulation of the atmosphere. The view of the atmospheric general circulation presented here focuses not on Earth’s general circulation as such but on a continuum of idealized circulations with axisymmetric flow statistics. Analyses of observational data for Earth’s atmosphere, simulations with idealized general circulation models, and theoretical considerations suggest how characteristics of the tropical Hadley circulation, of the extratropical circulation, and of atmospheric macroturbulence may depend on parameters such as the planet radius and rotation rate and the strength of the differential heating at the surface.
381 citations
TL;DR: A review of different methods of tabulating data from the Sepkoski database reveals 18 intervals during the Phanerozoic have peaks of both magnitude and rate of extinction that appear in each tabulating scheme, demonstrating that mass extinctions are not a homogeneous group of events.
Abstract: Recent analyses of Sepkoski’s genus-level compendium show that only three events form a statistically separate class of high extinction intensities when only post-Early Ordovician intervals are considered, but geologists have called numerous events mass extinctions. Is this a conflict? A review of different methods of tabulating data from the Sepkoski database reveals 18 intervals during the Phanerozoic have peaks of both magnitude and rate of extinction that appear in each tabulating scheme. These intervals all fit Sepkoski’s definition of mass extinction. However, they vary widely in timing and effect of extinction, demonstrating that mass extinctions are not a homogeneous group of events. No consensus has been reached on the kill mechanism for any marine mass extinction. In fact, adequate data on timing in ecologic, rather than geologic, time and on geographic and environmental distribution of extinction have not yet been systematically compiled for any extinction event.
380 citations
TL;DR: The Cambrian “explosion” is a unique episode in Earth history, when essentially all the animal phyla first appear in the fossil record and is best understood as being the result of the interplay of the combinatorial bilaterian developmental system and the increase in the number of needs the first bilaterians had to meet as complex ecological interactions developed.
Abstract: The Cambrian “explosion” is a unique episode in Earth history, when essentially all the animal phyla first appear in the fossil record A variety of environmental, developmental (genetic), and ecological explanations for this complex and somewhat protracted event are reviewed, with a focus on how well each explains the observed increases in disparity and diversity, the time of onset of the radiation, its duration, and its uniqueness The increase in disparity (the origin of the phyla) and diversity are best understood as being the result of the interplay of the combinatorial bilaterian developmental system and the increase in the number of needs the first bilaterians had to meet as complex ecological interactions developed The time of onset is constrained by the evolution of the environment, whereas its duration appears to be controlled primarily by rates of developmental innovation The uniqueness of the event is either due to ensuing developmental limitation, to ecological saturation, or simply to the exhaustion of ecologically viable morphologies that could be produced by the nascent bilaterian developmental system
379 citations
TL;DR: The discovery of the first chemically produced mass-independent isotope effect in 1983 by Thiemens & Heidenreich opened a broad variety of applications, including physical chemistry studies, atmospheric chemistry, paleoclimatology, biologic primary productivity assessment, Solar System origin and evolution, planetary atmospheres (Mars), and the origin of life in Earth's earliest environment.
Abstract: The discovery of the first chemically produced mass-independent isotope effect in 1983 by Thiemens & Heidenreich opened a broad variety of applications, including physical chemistry studies, atmospheric chemistry, paleoclimatology, biologic primary productivity assessment, Solar System origin and evolution, planetary atmospheres (Mars), and the origin and evolution of life in Earth's earliest environment. This chapter reviews the history of the field as well as all of the various applications since the first report of the mass-independent isotope effect.
358 citations
TL;DR: The occurrence of unusual high-Mg andesite (HMA) characterizes the Setouchi volcanic belt in SW Japan, which was activated at 137±10 Ma by subduction of the young and hot Shikoku Basin lithosphere into the high-temperature upper mantle as mentioned in this paper.
Abstract: The occurrence of unusual high-Mg andesite (HMA) characterizes the Setouchi volcanic belt in SW Japan, which was activated at 137±10 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% H2O, 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 intru
304 citations
TL;DR: The field of M ¨ ossbauer spectroscopy (MS) has recently enjoyed renewed visibility in the diverse geoscience communities as a result of the inclusion of MS spectrograms in the literature.
Abstract: The field of M ¨ ossbauer spectroscopy (MS) has recently enjoyed renewed visibility in the diverse geoscience communities as a result of the inclusion of M ¨ ossbauer
TL;DR: In this article, experimental and field data that document a progressive increase in the D/H ratio of most organic hydrogen at the bulk and molecular levels, and suggest that the transfer of hydrogen from water to organic matter is the most important mechanism leading to those changes.
Abstract: Changes in the D/H ratio of sedimentary organic matter (SOM) during thermal maturation have been difficult to interpret because the effects of hydrogen exchange and kinetic fractionations are confounded in natural samples. Recent analytical developments have significantly improved our understanding of the responsible mechanisms. In this paper, we review experimental and field data that document a progressive increase in the D/H ratio of most organic hydrogen at the bulk and molecular levels, and suggest that the transfer of hydrogen from water to organic matter is the most important mechanism leading to those changes. SOM and water in natural petroleum systems approach a pseudoequilibrium D/H fractionation of about −80 to −110‰. D/H ratios of organic hydrogen can preserve quantitative information about paleoclimate throughout diagenesis, and some qualitative information through catagenesis.
TL;DR: In this article, the authors show that small craters can sometimes be used to derive meaningful age constraints and that distant secondaries globally dominate the number of small lunar craters; this would invalidate part of production functions that have been widely used for age dating.
Abstract: Small craters (less than one kilometer diameter) can be primary craters produced by impact of interplanetary debris, or they can be secondary craters produced by fallback of high-velocity ejecta blocks from much larger but infrequent primary impacts. The prevalent assumption over recent decades has been that primaries are most abundant, so most small craters are independent random events and can be used for dating. However, recent results from Europa and Mars support the early theory that distant secondaries globally dominate the number of small lunar craters; this would invalidate part of production functions that have been widely used for age dating. Crater excavation results in higher mean ejection velocities for smaller fragments, resulting in a steeper size-frequency distribution for secondary craters than is produced by the same size-frequency distribution of interplanetary debris. This review also discusses how small craters can sometimes be used to derive meaningful age constraints.
TL;DR: Aerogel is an ultra-low-density material that can be used to capture small particles incident upon it at speeds in excess of 1 km s−1.
Abstract: Aerogel is an ultra-low-density material that can be used to capture small particles incident upon it at speeds in excess of 1 km s−1. This permits capture of cosmic dust in space where the high speeds usually result in destructive impact events. The performance of aerogel in laboratory impact tests is described. Completely intact capture is rare; most studies show that between 10% to 100% of the incident particle's mass is captured. However, in all cases unaltered domains were found in the particles captured in the laboratory at speeds up to 6 or 7 km s−1. Several analytic techniques can be applied in situ to particles captured in aerogel, yielding data on the preimpact composition of the particle. Extraction techniques for removing small particles from aerogel are described, and after extraction, handling and analysis in the laboratory can proceed as for any small-sized particle. Coupled with the survival of intact regions in the captured particles, this allows detailed identification of the com...
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TL;DR: A review of observations and theories regarding binary asteroids and binary trans-Neptunian objects [collectively, binary minor planets (BMPs)] is presented in this paper, where the most promising models invoke rotational disruption for the smallest, shortest-lived objects (the asteroids nearest to Earth), consistent with the observed fast rotation of these bodies.
Abstract: A review of observations and theories regarding binary asteroids and binary transNeptunian objects [collectively, binary minor planets (BMPs)] is presented. To date, these objects have been discovered using a combination of direct imaging, lightcurve analysis, and radar. They are found throughout the Solar System, and present a challenge for theorists modeling their formation in the context of Solar System evolution. The most promising models invoke rotational disruption for the smallest, shortestlived objects (the asteroids nearest to Earth), consistent with the observed fast rotation of these bodies; impacts for the larger, longer-lived asteroids in the main belt, consistent with the range of size ratios of their components and slower rotation rates; and mutual capture for the distant, icy, trans-Neptunian objects, consistent with their large component separations and near-equal sizes. Numerical simulations have successfully reproduced key features of the binaries in the first two categories; the third remains to be investigated in detail.
TL;DR: For ten earthquakes in nonmagmatic settings, there are credible published accounts of pre-earthquake deformation-rate changes lasting hundreds of seconds to more than a decade.
Abstract: For ten earthquakes in nonmagmatic settings, there are credible published accounts of pre-earthquake deformation-rate changes lasting hundreds of seconds to more than a decade. Although most M > 7.5 earthquakes have occurred without detectable pre-earthquake deformation, the detection threshold for aseismic deformation remains high, in that aseismic slip with moment equivalent to an M5 earthquake would in most (although not all) cases have been missed. Interseismic deformation rates vary without being followed by earthquakes, and a strain-rate change prior to the 1989 Mw6.9 Loma Prieta, California, earthquake is shown to be similar in size to many other rate changes that have occurred since that time. Most examples of pre-earthquake aseismic deformation lasting hundreds of seconds or more probably originate adjacent to, or downdip of, the seismic rupture plane, rather than within the zone that undergoes seismic failure.
TL;DR: The meaning of the word "Planet" has been the subject of much controversy over the past 15 years as discussed by the authors, and it is clear that scientists do not have a widely accepted or clear definition of what a planet is, and both scientists and the public are confused by its use in various contexts.
Abstract: The past 15 years have brought about a revolution in our understanding of our Solar System and other planetary systems. During this time, discoveries include the first Kuiper belt objects (KBOs), the first brown dwarfs, and the first extrasolar planets. Although discoveries continue apace, they have called into question our previous perspectives on planets, both here and elsewhere. The result has been a debate about the meaning of the word “planet” itself. It is clear that scientists do not have a widely accepted or clear definition of what a planet is, and both scientists and the public are confused (and sometimes annoyed) by its use in various contexts. Because “planet” is a very widely used term, it seems worth the attempt to resolve this problem. In this essay, we try to cover all the issues that have come to the fore and bring clarity (if not resolution) to the debate.
TL;DR: In this article, a bubble plume theory is applied to the dynamics of lake eruptions and the various kinetic and dynamic processes involved are examined and quantified, and theoretical calculations are consistent with the high exit velocities and eruption columns inferred from observations.
Abstract: Dissolved gas in liquid is able to power violent eruptions. Two kinds of such gas-driven eruptions are known in nature: explosive volcanic eruptions driven by dissolved H2O in magma at high temperatures and lake eruptions driven by dissolved CO2 in water at low temperatures. There are two known occurrences of lake eruptions, one in 1984 (Lake Monoun) and one in 1986 (Lake Nyos), both in Cameroon, Africa. The erupted CO2 gas asphyxiated ∼1700 people in the Lake Nyos eruption and 37 people at Lake Monoun. Here we review experimental simulations of CO2-driven water eruptions and dynamic models of such eruptions, and a bubble plume theory is applied to the dynamics of lake eruptions. Field evidence, experimental results, and theoretical models show that lake eruptions can be violent, and theoretical calculations are consistent with the high exit velocities and eruption columns inferred from observations. Furthermore, the dynamics of lake degassing experiments are consistent with theoretical models. Other kinds of gas-driven eruptions are possible and may have occurred in nature in the past. A concentrated and large release of methane gas or hydrate from marine sediment may result in an ocean eruption. Furthermore, injection of liquid CO2 into oceans might also lead to ocean eruptions if care is not taken. The various kinetic and dynamic processes involved are examined and quantified.
TL;DR: The level of achievable stratigraphic resolution determines the nature of the many ecological, evolutionary, and geological questions for which a reasonable answer may be expected as discussed by the authors, which is the case for many questions about rates of geological, geochemical, and evolutionary processes.
Abstract: The level of achievable stratigraphic resolution determines the nature of the many ecological, evolutionary, and geological questions for which a reasonable answer may be expected. Advances in correlation techniques and in high-resolution radiometric dating and their integration with the fossil record through quantitative biostratig- raphy and potentially orbital cyclicity now allows many questions about rates of geological, geochemical, and evolutionary processes to be extended into deep time.
TL;DR: In recognition of the contributions of Norman Phillips and Joseph Smagorinsky to the field of numerical weather prediction (NWP), a symposium was held in 2003; this account is an amplification of a talk presented there as mentioned in this paper.
Abstract: In recognition of the contributions of Norman Phillips and Joseph Smagorinsky to the field of numerical weather prediction (NWP), a symposium was held in 2003; this account is an amplification of a talk presented there. Ideas anticipating the advent of NWP, the first technically successful numerical weather forcast, and the subsequent progression of NWP to a mature discipline are described, with special emphasis on the work of Phillips and Smagorinsky and their mentor Jule Charney.
TL;DR: The race is not to the swift, nor the battle to the strong, neither yet bread to the wise, nor riches to men of understanding, nor yet favour to men with skill; but time and chance happeneth to them all.
Abstract: I returned and saw under the sun, that the race is not to the swift, nor the battle to the strong, neither yet bread to the wise, nor yet riches to men of understanding, nor yet favour to men of skill; but time and chance happeneth to them all. Ecclesiastes 9:11 (King James version)