Showing papers in "Annual Review of Earth and Planetary Sciences in 2005"

THE EARLY HISTORY OF ATMOSPHERIC OXYGEN: Homage to Robert M. Garrels

Abstract: ▪ Abstract This paper reviews the Precambrian history of atmospheric oxygen, beginning with a brief discussion of the possible nature and magnitude of life before the evolution of oxygenic photosynthesis. This is followed by a summary of the various lines of evidence constraining oxygen levels through time, resulting in a suggested history of atmospheric oxygen concentrations. Also reviewed are the various processes regulating oxygen concentrations, and several models of Precambrian oxygen evolution are presented. A sparse geologic record, combined with uncertainties as to its interpretation, yields only a fragmentary and imprecise reading of atmospheric oxygen evolution. Nevertheless, oxygen levels have increased through time, but not monotonically, with major and fascinating swings to both lower and higher levels.

The north anatolian fault: a new look

Abstract: Dedicated to the memory of three pioneers, Ihsan Ketin, Sirri Erinc and Melih Tokay, and a recent student, Aykut Barka, who burnt himself out in pursuit of the mysteries of the North Anatolian Fault. ▪ Abstract The North Anatolian Fault (NAF) is a 1200-km-long dextral strike-slip fault zone that formed by progressive strain localization in a generally westerly widening right-lateral keirogen in northern Turkey mostly along an interface juxtaposing subduction-accretion material to its south and older and stiffer continental basements to its north. The NAF formed approximately 13 to 11 Ma ago in the east and propagated westward. It reached the Sea of Marmara no earlier than 200 ka ago, although shear-related deformation in a broad zone there had already commenced in the late Miocene. The fault zone has a very distinct morphological expression and is seismically active. Since the seventeenth century, it has shown cyclical seismic behavior, with century-long cycles beginning in the east and progressing westwa...

Earthquake triggering by static, dynamic, and postseismic stress transfer

Abstract: ▪ Abstract Earthquake triggering is the process by which stress changes associated with an earthquake can induce or retard seismic activity in the surrounding region or trigger other earthquakes at great distances. Calculations of static Coulomb stress changes associated with earthquake slip have proven to be a powerful tool in explaining many seismic observations, including aftershock distributions, earthquake sequences, and the quiescence of broad, normally active regions following large earthquakes. Delayed earthquake triggering, which can range from seconds to decades, can be explained by a variety of time-dependent stress transfer mechanisms, such as viscous relaxation, poroelastic rebound, or afterslip, or by reductions in fault friction, such as predicted by rate and state constitutive relations. Rapid remote triggering of earthquakes at great distances (from several fault lengths to 1000s of km) is best explained by the passage of transient (dynamic) seismic waves, which either immediately induce ...

THE EDIACARA BIOTA: Neoproterozoic Origin of Animals and Their Ecosystems

Abstract: ▪ Abstract The Ediacara biota (575–542 Ma) marks the first appearance of large, architecturally complex organisms in Earth history. Present evidence suggests that the Ediacara biota included a mixture of stem- and crown-group radial animals, stem-group bilaterian animals, “failed experiments” in animal evolution, and perhaps representatives of other eukaryotic kingdoms. These soft-bodied organisms were preserved under (or rarely within) event beds of sand or volcanic ash, and four distinct preservational styles (Flinders-, Fermeuse-, Conception-, and Nama-style) profoundly affected the types of organisms and features that could be preserved. Even the earliest Ediacaran communities (575–565 Ma) show vertical and lateral niche subdivision of the sessile, benthic, filter-feeding organisms, which is strikingly like that of Phanerozoic and modern communities. Later biological and ecological innovations include mobility (>555 Ma), calcification (550 Ma), and predation (<549 Ma). The Ediacara biota abruptly disa...

Real-Time Seismology and Earthquake Damage Mitigation

Abstract: ■ 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.

Representing model uncertainty in weather and climate prediction

Abstract: ▪ Abstract Weather and climate predictions are uncertain, because both forecast initial conditions and the computational representation of the known equations of motion are uncertain. Ensemble prediction systems provide the means to estimate the flow-dependent growth of uncertainty during a forecast. Sources of uncertainty must therefore be represented in such systems. In this paper, methods used to represent model uncertainty are discussed. It is argued that multimodel and related ensembles are vastly superior to corresponding single-model ensembles, but do not provide a comprehensive representation of model uncertainty. A relatively new paradigm is discussed, whereby unresolved processes are represented by computationally efficient stochastic-dynamic schemes.

Atmospheric moist convection

Abstract: ▪ Abstract Various forms of atmospheric moist convection are reviewed through a consideration of three prevalent regimes: stratocumulus; trade-wind; and deep, precipitating, maritime convection. These regimes are chosen because they are structural components of the general circulation of the atmosphere and because they highlight distinguishing features of this polymorphous phenomenon. In particular, the ways in which varied forms of moist convection communicate with remote parts of the flow through mechanisms other than the rearrangement of fluid parcels are emphasized. These include radiative, gravity wave, and/or microphysical (precipitation) processes. For each regime, basic aspects of its phenomenology are presented along with theoretical frameworks that have arisen to help rationalize the phenomenology. Recent developments suggest that the increased capacity for numerical simulation and increasingly refined remote sensing capabilities bodes well for major advances in the coming years.

Early crustal evolution of mars 1

Abstract: ▪ Abstract The bulk of the ∼50-km-thick Martian crust formed at ∼4.5 Gyr B.P., perhaps from a magma ocean. This crust is probably a basaltic andesite or andesite and is enriched in incompatible and heat-producing elements. Later additions of denser basalt to the crust were volumetrically minor, but resurfaced significant portions of the Northern hemisphere. A significant fraction of the total thickness of the crust was magnetized prior to 4 Gyr B.P., with the magnetization later selectively removed by large impacts. Early large impacts also modified the hemispheric contrast in crustal thickness (the dichotomy), which was possibly caused by long-wavelength mantle convection. Subsequent Noachian modification of the crust included further impacts, significant fluvial erosion, and volcanism associated with the formation of the Tharsis rise. Remaining outstanding questions include the origin of the dichotomy and the nature of the magnetic anomalies.

THE Hf-W ISOTOPIC SYSTEM AND THE ORIGIN OF THE EARTH AND MOON

Abstract: ▪ Abstract The Earth has a radiogenic W-isotopic composition compared to chondrites, demonstrating that it formed while 182Hf (half-life 9 Myr) was extant in Earth and decaying to 182W. This implies that Earth underwent early and rapid accretion and core formation, with most of the accumulation occurring in ∼10 Myr, and concluding approximately 30 Myr after the origin of the Solar System. The Hf-W data for lunar samples can be reconciled with a major Moon-forming impact that terminated the terrestrial accretion process ∼30 Myr after the origin of the Solar System. The suggestion that the proto-Earth to impactor mass ratio was 7:3 and occurred during accretion is inconsistent with the W isotope data. The W isotope data is satisfactorily modeled with a Mars-sized impactor on proto-Earth (proto-Earth to impactor ratio of 9:1) to form the Moon at ∼30 Myr.

Mathematical Modeling of Whole Landscape Evolution

Abstract: ▪ Abstract The mathematical modeling of landform evolution consists of two components: the processes represented (i.e., considered dominant) in the model and the (typically computer) model representation of these processes. This review discusses the current debates surrounding processes represented in landform evolution. The potential impact on both evolving landforms and computer model structure is discussed. Issues specifically discussed include (a) the fundamental nature of mass conservation and the role of detachment- and transport-limited processes in mass conservation equations, (b) the interaction between detachment- and transport-limitation in channels, (c) the role of hillslope erosion and soil properties and their interaction with channel processes, (d) the interactions with tectonics when applying these models at large scale, (e) depositional structures and implications for paleo-climatic interpretation, (f) engineering applications of these models, and (g) numerical issues in the computer imp...

Evolution of the continental lithosphere

Abstract: ▪ Stable cratons and stable continental platforms are salient features of the Earth. Mantle xenoliths provide detailed data on deep structure. Cratonal lithosphere is about 200 km thick. It formed in the Archean by processes analogous to modern tectonics and has been stable beneath the larger cratons since that time. Its high viscosity, high yield strength, and chemical buoyancy protected it from being entrained by underlying stagnant lid convection and by subduction. Chemically buoyant mantle does not underlie platforms. Platform lithosphere has gradually thickened with time as convection waned as the Earth's interior cooled. The thermal contraction associated with this thickening causes platforms to subside relative to cratons. At present, the thickness of platform lithosphere is comparable to that of cratonal lithosphere.

Evolution of Fish-Shaped Reptiles (reptilia: Ichthyopterygia) in Their Physical Environments and Constraints

Abstract: ▪ Abstract Ichthyosaurs were a group of Mesozoic marine reptiles that evolved fish-shaped body outlines. They are unique in several anatomical characters, including the possession of enormous eyeballs sometimes exceeding 25 cm and an enlarged manus with sometimes up to 20 bones in a single digit, or 10 digits per manus. They are also unique in that their biology has been studied from the perspective of physical constraints, which allowed estimation of such characteristics as optimal cruising speed, visual sensitivity, and even possible basal metabolic rate ranges. These functional inferences, although based on physical principles, obviously contain errors arising from the limitations of fossilized data, but are necessarily stronger than the commonly made inferences based on superficial correlations among quantities without mechanical or optical explanations for why such correlations exist.

Are the alps collapsing

Abstract: ▪ Abstract Orogenic collapse is a process that transfers gravitational potential energy from regions of high potential energy to regions of lower potential energy. This transfer is classically considered to be accomplished by extension in the orogenic core and by synchronous shortening in foreland regions of the orogen. Not all extensional features in collisional mountain belts need, however, reflect orogenic collapse. Normal faulting, thrust faulting, and strike-slip faulting are all active in different parts of the Alps today and reflect complex local responses to ongoing Europe-Adria convergence. The Western Alps is the only area today where extension and shortening radial to orogen trend occur synchronously and where orogenic collapse may be an important process. Elsewhere in the Alps, normal faults are oriented at a high angle to orogen trend and were primarily active in Oligocene and Miocene time. Most present-day activity in the Central and Eastern Alps is on strike-slip faults that are accommodati...

Lakes beneath the ice sheet: The occurrence, analysis, and future exploration of Lake Vostok and other Antarctic subglacial lakes

Abstract: ▪ Abstract Airborne geophysics has been used to identify more than 100 lakes beneath the ice sheets of Antarctica. The largest, Lake Vostok, is more than 250 km in length and 1 km deep. Subglacial lakes occur because the ice base is kept warm by geothermal heating, and generated meltwater collects in topographic hollows. For lake water to be in equilibrium with the ice sheet, its roof must slope ten times more than the ice sheet surface. This slope causes differential temperatures and melting/freezing rates across the lake ceiling, which excites water circulation. The exploration of subglacial lakes has two goals: to find and understand the life that may inhabit these unique environments and to measure the climate records that occur in sediments on lake floors. The technological developments required for in situ measurements mean, however, that direct studies of subglacial lakes may take several years to happen.

Molecular approaches to marine microbial ecology and the marine nitrogen cycle

Abstract: ▪ Abstract Microbes are recognized as important components of the Earth system, playing key roles in controlling the composition of the atmosphere and surface waters, forming the basis of the marine food web, and the cycling of chemicals in the ocean. A revolution in microbial ecology has occurred in the past 15–20 years with the advent of rapid methods for discovering and sequencing the genes of uncultivated microbes from natural environments. Initially based on sequences from the 16S rRNA gene, this revolution made it possible to identify microorganisms without first cultivating them, to discover and characterize the immense previously unsuspected diversity of the microbial world, and to reconstruct the evolutionary relationships among microbes. Subsequent focus on functional genes, those that encode enzymes that catalyze biogeochemical transformations, and current work on larger DNA fragments and entire genomes make it possible to link microbial diversity to ecosystem function. These approaches have yi...