Global Data Compilation Research Articles

Leaf venation: structure, function, development, evolution, ecology and applications in the past, present and future

The design and function of leaf venation are important to plant performance, with key implications for the distribution and productivity of ecosystems, and applications in paleobiology, agriculture and technology. We synthesize classical concepts and the recent literature on a wide range of aspects of leaf venation. We describe 10 major structural features that contribute to multiple key functions, and scale up to leaf and plant performance. We describe the development and plasticity of leaf venation and its adaptation across environments globally, and a new global data compilation indicating trends relating vein length per unit area to climate, growth form and habitat worldwide. We synthesize the evolution of vein traits in the major plant lineages throughout paleohistory, highlighting the multiple origins of individual traits. We summarize the strikingly diverse current applications of leaf vein research in multiple fields of science and industry. A unified core understanding will enable an increasing range of plant biologists to incorporate leaf venation into their research.

Soils as pacemakers and limiters of global silicate weathering

The weathering and erosion processes that produce and destroy regolith are widely recognized to be positively correlated across diverse landscapes. However, conceptual and numerical models predict some limits to this relationship that remain largely untested. Using new global data compilations of soil production and weathering rates from cosmogenic nuclides and silicate weathering fluxes from global rivers, we show that the weathering-erosion relationship is capped by certain ‘speed limits’. We estimate a soil production speed limit of between 320 to 450tkm−2yr−1 and the associated weathering rate speed limit of roughly 150tkm−2yr−1. These limits appear to be valid for a range of lithologies, and also extend to mountain belts, where soil cover is not continuous and erosion rates outpace soil production. We argue that the presence of soil and regolith is a requirement for high weathering fluxes from a landscape, and that rapidly eroding, active mountain belts are not the most efficient sites for weathering.

Citizen scientists analyzing tropical cyclone intensities

A new crowd sourcing project called CycloneCenter enables the public to analyze historical global tropical cyclone (TC) intensities. The primary goal of CycloneCenter, which launched in mid‐September, is to resolve discrepancies in the recent global TC record arising principally from inconsistent development of tropical cyclone intensity data. The historical TC record is composed of data sets called “best tracks,” which contain a forecast agency's best assessment of TC tracks and intensities. Best track data have improved in quality since the beginning of the geostationary satellite era in the 1960s (because TCs could no longer disappear from sight). However, a global compilation of best track data (International Best Track Archive for Climate Stewardship (IBTrACS)) has brought to light large interagency differences between some TC best track intensities, even in the recent past [Knapp et al., 2010Knapp et al., 2010]. For example, maximum wind speed estimates for Tropical Cyclone Gay (1989) differed by as much as 70 knots as it was tracked by three different agencies.

Mo isotope and trace element patterns of Lower Cambrian black shales in South China: Multi-proxy constraints on the paleoenvironment

The Precambrian/Cambrian boundary marks a critical interval in Earth history. Paleoenvironmental changes of the oceans have been suggested as a possible explanation for some significant events such as the marine biological evolution (“Cambrian explosion”). Here we report a remarkable variation range in trace element, iron speciation and molybdenum isotope signatures of black shales from the Early Cambrian Dingtai profile (Guizhou province) and three synsedimentary polymetallic Ni–Mo–(PGE–Au) sulfide ore deposits (Dazhuliushui and Maluhe in Guizhou province, and Sancha in Hunan province) on the Yangtze Platform, South China. Based on the (isotope) geochemical features, we classify the Dingtai profile into three intervals: interval 1 (0–1m) has extreme metal and TOC enrichment and heavy δ98/95Mo values. This unit has all features of a euxinic environment, and is then followed by interval 2 (1–11m) with variable δ98/95Mo composition. Elevated contents of redox-sensitive elements and their ratios, and relatively high FeHR/FeT ratios (“reactive iron”) suggest anoxic conditions. The overlying interval 3 (11–33m) reveals oxic to suboxic conditions with generally light δ98/95Mo values in the lowermost part and fluctuant δ98/95Mo values in the uppermost part, and relatively low redox-sensitive element contents. We propose a model of a partly closed ocean basin with periodic replenishment together with changing redox conditions for the remarkable variability of δ98/95Mo values. Light δ98/95Mo values indicate restricted seawater circulation dominated by local continental input, periodically replenished by fresh seawater with heavy δ98/95Mo.A global compilation of Mo isotope data from black shales indicates that the Mo isotopic variations have a consistent temporal trend, reflecting the oxygen evolution of the oceans. Relatively light δ98/95Mo values of the Lower Cambrian black shales compared to those of modern euxinic sediments are indicative of more widespread anoxic marine environments during the Early Cambrian.

An internally consistent, probabilistic, determination of ridge-axis hydrothermal fluxes from basalt-hosted systems

High-temperature hydrothermal systems at mid-ocean ridges play a critical role in global geochemical cycles. Most of the magmatic heat driving hydrothermal circulation along the global mid-ocean ridge system is released into basalt-hosted systems exemplified by intermediate- to fast-spreading ridges. Constraints on the fluid and chemical fluxes associated with these systems come from the compositions of high-temperature hydrothermal vent fluids and the compositions of altered sheeted dikes. Global data compilations of both of these data types, including 20 mineral components, 10 major fluid species, 13 trace elements and 6 isotope ratios, have been jointly fit using a numerical Bayesian inversion procedure. This new approach provides the first internally consistent estimates of fluid and chemical fluxes, with rigorously quantified uncertainties, for a broad suite of elements. The resulting global fluid flux is 8.0±2.1×1012kgyr−1, at a water-dike mass ratio of 0.92, sufficient to cool the sheeted dike complex from magmatic to hydrothermal temperatures and remove ~50% of the latent heat of crystallization of the plutonic complex. For conservative elements, the fluxes represent inputs into the ocean and should allow more accurate models of the controls on modern and paleo-seawater chemistry to be developed.

Cervical cancer and the human immunodeficiency virus: A review

Globally cervical cancer is one of the commonest cancers in women. It comprises approximately 12% of all cancers and is the commonest cancer in women in developing countries. The most recent compilation of global data indicates that an estimated 490 000 new cases of cervical cancer occur annually worldwide and nearly 80% of these are in developing countries, where screening programmes are not well established and are poorly organised. Cervical cancer is the leading cause of cancer death among women. It is estimated that 270 000 women die annually from cervical cancer, 85% of them in low-resource nations.1-3 In Africa, cervical cancer comprises 23.3% of all cancers in women.4 According to the South African National Cancer Registry (NCR) data, the lifetime risk for the development of cervical cancer in 1998 was 1 in 26 for South African women and 1 in 21 for black South African women.5 These are believed to be minimal rates, as the registry publishes only data collected from the pathology laboratories and is not a population-based cancer registry. HIV/ AIDS poses a severe threat to global health. In addition, the HIV epidemic has hit hardest in regions of high prevalence of cervical dysplasia and cancer. The HIV epidemic in South Africa is one of the worst in the world. The prevalence of HIV among South African women attending antenatal clinics in 2006 was 29.1%.6 With improved access to antiretroviral therapy, women are expected to live longer as the risk of death from opportunistic infections decreases. It is assumed that the incidence of cervical cancer and the prevalence of precursor lesions will increase, especially in countries that lack well-organised cervical screening. However, this remains to be seen.

Historical variation of the geomagnetic axial dipole

The geomagnetic axial dipole (hereinafter denoted g 1 0 ) is the largest component of our planet’s magnetic field. Its magnitude determines the morphology of solar-terrestrial electrical current systems and it is the most fundamental diagnostic property of the core-generated geodynamo. Elucidating past and future variations of g 1 0 ( t ) is consequently of central importance in geomagnetism. Previous historical geomagnetic field models, such as gufm1 of Jackson et al. [Jackson, A., Jonkers, A.R.T., Walker, M.R., 2000. Four centuries of geomagnetic secular variation from historical records. Philos. Trans. R. Soc. Lond. A 358, 957–990], used direct observations to constrain g 1 0 ( t ) only after 1840 A.D.; before this time a crude linear extrapolation of the post-1840 A.D. rate of change (15 nT/year) was employed. In this contribution I construct historical field models with g 1 0 ( t ) instead constrained from 1590 A.D. to 1840 A.D. by an archaeointensity dataset compiled by Korte et al. [Korte, M., Genevey, A., Constable, C.G., Frank, U., Schnepp, E., 2005. Continuous geomagnetic field models for the past 7 millennia. 1. A new global data compilation. Geochem. Geophys. Geosyst. 6, doi:10.1029/2004GC000800]. A range of possible linear models of the form g 1 0 ( t ) = g 1 0 ( 1840 ) + β ( t − 1840 ) are first explored; β = 2.74 ± 42.32 nT/year is found to explain the archaeointensity dataset with maximum likelihood, consistent with the recent findings of Gubbins et al. [Gubbins, D., Jones, A.L., Finlay, C.C., 2006. Fall in Earth’s magnetic field is erratic. Science 312, 900–902]. Relaxing the linear constraint in an effort to find more physically plausible models, I find it is necessary to artificially increase the weight given to the archaeointensity data in order to obtain acceptable models. Despite satisfactorily explaining both the historical and archaeointensity data, and possessing reasonable spatial and temporal complexity, such free evolution models perform worse than the simpler linearly constrained models when tested against the independent dataset of Gallet et al. [Gallet, Y., Genevey, A., Fluteau, F., 2005. Does Earth’s magnetic field secular variation control centennial climate change? Earth Plan. Sci. Lett. 236, 159–173]. Bayesian model comparison techniques indicate that a model ( gufm1-g10c) involving no change in g 1 0 ( t ) between 1590 A.D. and 1840 A.D. is most probable given the presently available data and current modelling techniques. I propose that this new, empirically derived, constraint on the evolution of the geomagnetic axial dipole be incorporated into the next generation of historical field models.

Survival variability and population density in fish populations

To understand the processes that regulate the abundance and persistence of wild populations is a fundamental goal of ecology and a prerequisite for the management of living resources. Variable abundance data, however, make the demonstration of regulation processes challenging. A previously overlooked aspect in understanding how populations are regulated is the possibility that the pattern of variability--its strength as a function of population size--may be more than 'noise', thus revealing much about the characteristics of population regulation. Here we show that patterns in survival variability do provide evidence of regulation through density. Using a large, global compilation of marine, anadromous and freshwater fisheries data, we examine the relationship between the variability of survival and population abundance. The interannual variability in progeny survival increases at low adult abundance in an inversely density-dependent fashion. This pattern is consistent with models in which density dependence enters after the larval stage. The findings are compatible with very simple forms of density dependence: even a linear increase of juvenile mortality with adult density adequately explains the results. The model predictions explain why populations with strong regulation may experience large increases in variability at low densities. Furthermore, the inverse relationship between survival variability and the strength of density dependence has important consequences for fisheries management and recovery, and population persistence or extinction.

Simulation of global crop production with the ecosystem model DayCent

Agriculture has become a key element within the earth system as it changes global biogeochemical and water cycles, while global environmental change affects land productivity and thus future land-use decisions. To address these issues and their complex interdependency in a consistent modelling approach we adapted the agro-ecosystem model DayCent for the simulation of major crops at the global scale. Based on a global compilation of environmental and management data and an algorithm to calculate global planting dates, DayCent was parameterised and calibrated to simulate global yield levels for wheat, maize, rice and soybeans. Simulation results show that the DayCent model is able to reproduce the major effects of climate, soil and management on crop production. Average simulated crop yield per country agree well with agricultural statistics (Modelling efficiency is about 0.66 for wheat, rice and maize, and 0.32 for soybean) and spatial patterns of yields generally correspond to observed crop distributions and sub-national census data.

Modeling sensitivity of biodiffusion coefficient to seasonal bioturbation

Biodiffusion coefficient is the predominant parameter used to constrain biological activity in marine sediments. Bioturbation characterization is important because of the dominant role it plays on the flux determination through the sediment-water interface. Biological mixing is quantified through models of radionuclides diagenesis by both a biodiffusion coefficient (Db) and a mixed depth (L) under the basic steady-state assumption. Based on a new global compilation of radionuclide data in marine sediments and on previously published modeling results, we show that short-live radionuclides are perfectly devoted to quantify biological mixing for sediments associated with L 2 /Db lower than 125, representing the decay constant of the radionuclide. 75 % of the 234 Th-derived Db, and 79 % of the 7 Be-derived Db are concerned by this result. However, as transient regimes prevail within marine sediments, especially at a seasonal time scale and within the coastal and shelf environment, it is necessary to model their impacts on Db calculations. A transient model of radionuclide decay and transport is therefore used to perform extensive sensitivity tests of Db calculations in respect to seasonal mixing. Numerical tests of seasonal sensitivity indicate that 234 Th and 7 Be are the most sensitive tracers to seasonal biological mixing: the steady-state assumption remains valid and applicable for most of natural marine environments. However, systematic tests reveal that incorrect seasonal sensitivity of 234 Th is detected for marine environments with L 2 /Db lower than 10 and greater than 1000. In these cases, the apparent seasonal variations of the biological activity need to be corrected. The main parameter in selecting the appropriate radionuclide for field analyses is the dimensionless pulse, which defines the relative importance of decay time scale relative to the seasonal time scale. This pulse controls the relative extension of the domain of satisfactory sensitivity. Consequently, long-lived radionuclides ( 210 Pb and 228 Th) are not appropriate for predicting seasonal mixing, except for specific environments which display an unexpected sensitivity to seasonal mixing. These marine environments are characterized by a moderate biological mixing and a deep mixed-layer.

Assessing a Satellite-Era Perspective of the Global Water Cycle

Abstract The capability of a global data compilation, largely satellite based, is assessed to depict the global atmospheric water cycle’s mean state and variability. Monthly global precipitation estimates from the Global Precipitation Climatology Project (GPCP) and the Climate Prediction Center (CPC) Merged Analysis of Precipitation (CMAP) span from 1979 to 1999. Monthly global Special Sensor Microwave Imager (SSM/I)-based bulk aerodynamic ocean evaporation estimates span from June 1987 to December 1999. Global terrestrial evapotranspiration rates are estimated over a multidecade period (1975–99) using a global land model simulation forced by bias-corrected reanalysis data. Monthly total precipitable water (TPW) from the NASA Global Water Vapor Project (NVAP) spans from 1988 to 1999. The averaged annual global precipitation (P) and evaporation (E) estimates are out of balance by 5% or 24 000 (metric) gigatons (Gton) of water, which exceeds the uncertainty of global mean annual precipitation (∼±1%). For any given year, the annual flux imbalance can be on the order of 10% (48 000 Gton of water). However, observed global TPW interannual variations suggest a water flux imbalance on the order of 0.01% (48 Gton of water)—a finding consistent with a general circulation model (GCM) simulation. Variations in observationally based global P and E rates show weak monthly and interannual consistency, and depending on the choice of ocean evaporation data, the mean annual cycle of global E − P can be up to 5 times larger to that of TPW. The global ocean annual evaporation rates have as much as a ∼1% yr−1 increase during the period analyzed (1988–99), which is consistent in sign with most transient CO2 GCM simulations, but at least an order of magnitude larger. The ocean evaporation trends are driven by trends in SSM/I-retrieved near-surface atmospheric humidity and wind speed, and the largest year-to-year changes are coincident with transitions in the SSM/I fleet. In light of (potential) global water cycle changes in GCM projections, the ability to consistently detect or verify these changes in nature rests upon one or more of the following: quantification of global evaporation uncertainty, at least a twofold improvement in consistency between the observationally based global precipitation and evaporation variations, a two order of magnitude rectification between annual variations of E − P and precipitable water as well as substantial improvements in the consistency of their seasonal cycles, a critical reevaluation of intersatellite calibration for the relevant geophysical quantities used for ocean evaporation estimates, and the continuation of a dedicated calibration in this regard for future satellite transitions.

O.144 Controlled lower border split of mandibular body – Modification of BSSO

The cosmogenic meteoric 10Be that is produced in the atmosphere and mainly scavenged by rainfall is a valuable tool for determining dates and rates of Earth surface processes. A key prerequisite for its applications is the knowledge of the long-term 10Be depositional flux to Earth's surface. Previous efforts on obtaining 10Be depositional fluxes include general atmospheric circulation modelling (GCM), empirical fitting of rainfall 10Be records, and determining the inventory of soil profiles of known age. Here, we derive 10Be depositional fluxes from Holocene river terrace 10Be inventories across the Taiwan mountain belt. We measured 10Be and 9Be concentrations from three terrace profiles, with 14C ages ranging between 3.83 and 9.05 cal. kyr BP and sampling depths of up to 6.2 m.Based on 10Be inventories of our river terraces, the calculated long-term 10Be depositional fluxes vary from 0.32 to 0.49 × 106 at/cm2/yr in the Taiwan orogen. We identify partial Be retention, surface erosion, multi-phase sediment deposition, and incomplete sampling depth in these terraces as potential causes of flux underestimation. When accounting for each of these factors and their uncertainties, the resulting flux estimates of each terrace show an overlapping range of 0.66–0.88 × 106 at/cm2/yr. This newly constrained flux range representative over millennial timescales is thus recommended for Earth surface applications in the fast-eroding Taiwan orogen, especially in regions with similar climatic conditions as the studied terraces. When comparing to flux estimates from other approaches, the flux from the rainfall-based fitting equation exceeds our new terrace-derived flux by more than a factor of two. We consider such high flux to be unlikely for the Taiwan orogen, and suggest that the control of precipitation on the 10Be flux here may be overestimated in rainfall data fitting. The GCM-derived flux overestimates the 10Be depositional flux in this setting to a smaller degree (at least 23%), which is in accordance with findings from previous global data compilation of 10Be fluxes.

Phylogenetic and Growth Form Variation in the Scaling of Nitrogen and Phosphorus in the Seed Plants

Plant biomass and nutrient allocation explicitly links the evolved strategies of plant species to the material and energy cycles of ecosystems. Allocation of nitrogen (N) and phosphorus (P) is of particular interest because N and P play pivotal roles in many aspects of plant biology, and their availability frequently limits plant growth. Here we present a comparative scaling analysis of a global data compilation detailing the N and P contents of leaves, stems, roots, and reproductive structures of 1,287 species in 152 seed plant families. We find that P and N contents (as well as N : P) are generally highly correlated both within and across organs and that differences exist between woody and herbaceous taxa. Between plant organs, the quantitative form of the scaling relationship changes systematically, depending on whether the organs considered are primarily structural (i.e., stems, roots) or metabolically active (i.e., leaves, reproductive structures). While we find significant phylogenetic signals in the data, similar scaling relationships occur in independently evolving plant lineages, which implies that both the contingencies of evolutionary history and some degree of environmental convergence have led to a common set of rules that constrain the partitioning of nutrients among plant organs.

PATTERNS AND PROCESSES OF LATEST ORDOVICIAN GRAPTOLITE EXTINCTION AND RECOVERY BASED ON DATA FROM SOUTH CHINA

We have studied the pattern of graptolite species turnover during the latest Ordovician mass extinction based on four continuous Ashgillian to earliest Llandovery sections together with data from more than 30 other published sections. The studied sections represent relatively shallow-water and deeper-water belts in the Yangtze Platform region. Using temporally scaled range data, species diversities and extinction and origination probabilities have been calculated using several analytical methods, including a capture- mark-recapture method. We test the statistical significance of these results and the apparent taxonomic selectivity of extinction and origination via Monte Carlo simulations and contingency analysis. Graptolite species diversity within the Yangtze Platform rose steadily during the late Ashgill, until in the mid-late Paraorthograptus pacificusChron, when rising extinction risk overtook origination. Diversity dropped to very low levels during the early Hirnantian when extinction probabilities attained significantly elevated rates for a period of 600-900 Ky. The period of high extinction risk was followed immediately by a short period of very high origination probability. A second, short period of high extinction risk occurred at the end of Hirnantian time. The Hirnantian extinction events marked a change from relatively low, steady origination and extinction probabilities to a prolonged period of elevated extinction risk and highly variable origination probability that extended well into the Rhuddanian. Extinction and origination was highly selective during the Hirnantian and favored both the survival and diversification of the Normalograptidae relative to the Dicranograptidae, Diplograptidae, and Orthograptidae. The main phase of extinction in the latest Rawtheyan and early Hirnantian was coincident with continental glaciation in the Southern Hemisphere. The resulting changes in ocean circulation and oxygenation appear to have almost completely eliminated the preferred habitat for most graptolite species. The Yangtze Platform region, however, may have served as a refugium for many taxa that disappeared earlier in other regions as well as a host site for the initiation of graptolite rediversification. Following the end of the glaciation, conditions favorable for graptolite proliferation were restored but graptolite communities remained unstable for much of the late Hirnantian and early Rhuddanian. Accordingly, the Hirnantian mass extinction appears to have fundamentally altered graptolite species dynamics as well as clade dominance patterns. A full understanding of the history of life requires an expanded, hierarchical theory of evolution that gives to mass extinctions (and other levels of selection) an appropriate role in determining clade and diversity histories. INCE THE beginning of the scientific study of the fossil record it has been evident that the history of life is intermittently interrupted by widely spaced extinction events during which large fractions of the world's species diversity became extinct. The Late Ordovician was one such event, and graptolites were among the organisms that showed high rates of taxonomic turnover during this interval. Most previous studies of the Late Ordovician grap- tolite extinction (e.g., Melchin and Mitchell, 1991; Koren', 1991; Koren' and Bjerreskov, 1999) were based on attempts at global compilation of data from many separate sections and different zonal schemes. The range data themselves were gathered primar- ily from the published literature, and necessarily involved many different (and in some cases contradictory) systematic treatments of the graptolite faunas, as well as varying sampling intervals and intensities. However, more precise, quantitative data on the rate and magnitude of extinction are essential to understand the pro- cesses that underlay the extinction event. These data require a finely resolved chronology and consistent systematic treatment of the faunas. The present paper employs a large and revised compilation of graptolite species ranges based on our recollection and published data from 37 densely sampled sections in South China. These include four continuous sections (Wangjiawan and Fenxiang of

Helium not in store

The ratio of helium isotopes in some oceanic volcanoes seemed to demand a reservoir of virgin primordial gas in the Earth's mantle. In fact, that might not be necessary — a relief for other geophysical models. Degassing of the Earth's mantle through magmatism results in the irreversible loss of helium to space. As virtually all Earth's 3He is ‘primordial’, high 3He/4He ratios in ocean island basalts are generally taken as evidence for a primitive, unmelted reservoir in the deep Earth. A new global data compilation now shows that ocean island basalts displaying the strongest primordial signal are chemically and isotopically most like mid-ocean-ridge basalts, indicating a common melting history for continent and ocean crust formation via incomplete degassing. This suggests that there is no primordial undegassed reservoir of helium in the mantle, reconciling a long-standing paradox in mantle dynamics.

Evolution of helium isotopes in the Earth's mantle

Degassing of the Earth's mantle through magmatism results in the irreversible loss of helium to space, and high (3)He/(4)He ratios observed in oceanic basalts have been considered the main evidence for a 'primordial' undegassed deep mantle reservoir. Here we present a new global data compilation of ocean island basalts, representing upwelling 'plumes' from the deep mantle, and show that island groups with the highest primordial signal (high (3)He/(4)He ratios) have striking chemical and isotopic similarities to mid-ocean-ridge basalts. We interpret this as indicating a common history of mantle trace element depletion through magmatism. The high (3)He/(4)He in plumes may thus reflect incomplete degassing of the deep Earth during continent and ocean crust formation. We infer that differences between plumes and the upper-mantle source of ocean-ridge basalts reflect isolation of plume sources from the convecting mantle for approximately 1-2 Gyr. An undegassed, primordial reservoir in the mantle would therefore not be required, thus reconciling a long-standing contradiction in mantle dynamics.

Continuous geomagnetic field models for the past 7 millennia: 1. A new global data compilation

A global data set of archeomagnetic and paleomagnetic data covering the past 7000 years has been compiled. It consists of 16,085 results of inclination, 13,080 of declination, and 3188 of intensity for the time span 5000 BC to 1950 AD. Declination and inclination data come partly from existing databases and partly from original literature. A new global compilation of intensity data for the millennial scale is included. Data and dating uncertainties are discussed as we attempted to obtain an internally coherent data set. The global distribution of the data is very inhomogeneous in both time and space. All the data are compared to predictions from the previous 3000 year global model, CALS3K.1. This collection of data will be useful for global secular variation studies and geomagnetic field modeling, although southern hemisphere data are still underrepresented. In particular, we will use it in a further study to update and extend the existing global model, CALS3K.1. The huge increase in data compared to the previous compilation will result in significant changes from current models. As we might have missed some suitable data, we encourage the reader to notify us about any data that have not been included yet and might fit in, as improving our global millennial scale models remains our aim for the future. The data files described in this paper are available from the EarthRef Digital Archive (ERDA) at http://earthref.org/cgi‐bin/erda.cgi?n=331.

Ecosystem remodelling among vertebrates at the Permian–Triassic boundary in Russia

The mass extinction at the Permian-Triassic boundary, 251 million years (Myr) ago, is accepted as the most profound loss of life on record. Global data compilations indicate a loss of 50% of families or more, both in the sea and on land, and these figures scale to a loss of 80-96% of species, based on rarefaction analyses. This level of loss is confirmed by local and regional-scale studies of marine sections, but the terrestrial record has been harder to analyse in such close detail. Here we document the nature of the event in Russia in a comprehensive survey of 675 specimens of amphibians and reptiles from 289 localities spanning 13 successive geological time zones in the South Urals basin. These changes in diversity and turnover cannot be explained simply by sampling effects. There was a profound loss of genera and families, and simplification of ecosystems, with the loss of small fish-eaters and insect-eaters, medium and large herbivores and large carnivores. Faunal dynamics also changed, from high rates of turnover through the Late Permian period to greater stability at low diversity through the Early Triassic period. Even after 15 Myr of ecosystem rebuilding, some guilds were apparently still absent-small fish-eaters, small insect-eaters, large herbivores and top carnivores.

Thermal thickness and evolution of Precambrian lithosphere: A global study

The thermal thickness of Precambrian lithosphere is modeled and compared with estimates from seismic tomography and xenolith data. We use the steady state thermal conductivity equation with the same geothermal constraints for all of the Precambrian cratons (except Antarctica) to calculate the temperature distribution in the stable continental lithosphere. The modeling is based on the global compilation of heat flow data by Pollack et al. [1993] and more recent data. The depth distribution of heat‐producing elements is estimated using regional models for ∼300 blocks with sizes varying from 1°×1° to about 5°×5° in latitude and longitude and is constrained by laboratory, seismic and petrologic data and, where applicable, empirical heat flow/heat production relationships. Maps of the lateral temperature distribution at depths 50, 100, and 150 km are presented for all continents except Antarctica. The thermal thickness of the lithosphere is calculated assuming a conductive layer overlying the mantle with an adiabat of 1300°C. The Archean and early Proterozoic lithosphere is found to have two typical thicknesses, 200–220 km and 300–350 km. In general, thin (∼220 km) roots are found for Archean and early Proterozoic cratons in the Southern Hemisphere (South Africa, Western Australia, South America, and India) and thicker (>300 km) roots are found in the Northern Hemisphere (Baltic Shield, Siberian Platform, West Africa, and possibly the Canadian Shield). We find that the thickness of continental lithosphere generally decreases with age from >200 km beneath Archean cratons to intermediate values of 200±50 km in early Proterozoic lithosphere, to about 140±50 km in middle and late Proterozoic cratons. Using known crustal thickness, our calculated geotherms, and assuming that isostatic balance is achieved at the base of the lithosphere, we find that Archean and early Proterozoic mantle lithosphere is 1.5% less dense (chemically depleted) than the underlying asthenosphere, while middle and late Proterozoic subcrustal lithosphere should be depleted by ∼0.6–0.7%. Our results suggest three contrasting stages of lithosphere formation at the following ages: >2.5 Ga, 2.5–1.8 Ga, and <1.8 Ga. Ages of komatiites, greenstone belts, and giant dike swarms broadly define similar stages and apparently reflect secular changes in mantle temperature and, possibly, convection patterns.

A global isostatic gravity model of the Earth

The long-wavelength features of the external gravity field of the Earth contain the gravitational signal from deep-seated lateral mass and density inhomogeneities sustained by dynamic Earth mantle processes. To interpret the observed gravity field with respect to mantle dynamics and structures, it is essential first to remove the lithosphere-induced anomalous gravitational potential, which is generated by the topographic surface load and its isostatically compensating masses. Based upon the most recent global compilation of crustal thickness and density data and the age distribution of cooling oceanic lithosphere, residual topography and gravity are calculated by subtracting the ‘known’ crustal and oceanic lithosphere compensating masses and gravitational effects from the surface fields. Empirical admittances between residual topography and gravity are then computed to estimate the effective depths of the remaining compensating masses, which are not explained by the initial data and model assumptions. This additional compensation is eventually placed by adjusting the density in the uppermost mantle between the Moho and, on average, 70 km depth, with a maximum of 118 km under Tibet. The lithospheric mass distribution is used in a subsequent forward computation to create a global model of the lithosphere-induced gravitational potential. The resulting isostatic model is considered to be valid for spatial wavelengths longer than 500 km. The isostatic lithosphere model field, expressed in terms of both gravity and geoid heights, is subtracted from the observed free-air gravity field to yield a global set of 1° × 1° isostatic gravity disturbances and from a satellite-derived long-wavelength geoid to yield the isostatic residual geoid. The comparison of residual (mantle) gravity, residual topography and isostatic corrected gravity allows us to identify the main characteristics of the underlying mantle; for example, dynamic support by mantle flow of the North Atlantic topographic high. Applying the isostatic correction, the overall pattern of the geoid becomes smoother and the most pronounced features, which are separated in the observed geoid, tend to get connected to larger structures. These results stress the importance of separation of the lithospheric gravitational impact for a correct interpretation of the external gravity field, even in its very long-wavelength constituents. Also, the isostatic corrected geoid spectrum reveals a stronger decrease in power from degree 3 to degree 4 and degree 5 to degree 6, which is in accordance with seismological models of deep-mantle structures.