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The largest mass extinction occurred about 250 million years ago at the boundary between the Permian and the Triassic. At that time, almost all of the continents were part of [...]

Our studies in southern China have revealed a remarkable sulfur and strontium isotope excursion at the end of the Permian, along with a coincident concentration of impact-metamorphosed grains and kaolinite and a significant decrease in manganese, phosphorous, calcium, and microfossils (foraminifera). These data suggest that an asteroid or a comet hit the ocean at the end of Permian time and caused a rapid and massive release of sulfur from the mantle to the ocean-atmosphere system, leading to significant oxygen consumption, acid rain, and the most severe biotic crisis in the history of life on Earth. Keywords: mass extinctions, Permian, S-34/S-32, Sr-87/Sr-86, impact metamorphism, elements, clay minerals.

The fossil record of land plants is an obvious source of information on the dynamics of mass extinctions in the geological past. In conjunction with the end-Permian ecological crisis, [approximately equals] 250 million years ago, palynological data from East Greenland reveal some unanticipated patterns. We document the significant time lag between terrestrial ecosystem collapse and selective extinction among characteristic Late Permian plants. Furthermore, ecological crisis resulted in an initial increase in plant diversity, instead of a decrease. Paradoxically, these floral patterns correspond to a 'dead zone' in the end-Permian faunal record, characterized by a paucity of marine invertebrate megafossils. The time-delayed, end-Permian plant extinctions resemble modeled 'extinction debt' responses of multispecies metapopulations to progressive habitat destruction.

A computer simulation of North American end-Pleistocene human and large herbivore population dynamics correctly predicts the extinction or survival of 32 out of 41 prey species. Slow human population growth rates, random hunting, and low maximum hunting effort are assumed; additional parameters are based on published values. Predictions are close to observed values for overall extinction rates, human population densities, game consumption rates, and the temporal overlap of humans and extinct species. Results are robust to variation in unconstrained parameters. This fully mechanistic model accounts for megafaunal extinction without invoking climate change and secondary ecological effects., More than half of the large mammal biota of the Americas disappeared in a cataclysmic extinction wave at the very end of the Pleistocene (1, 2). This dramatic event, unparalleled [...]

Until the late Pleistocene era, 11,000 to 50,000 years ago, big, exotic mammals and flightless birds roamed the planet. Then, suddenly, they were gone. Who killed the Pleistocene megafauna? So [...]

The end-Triassic mass extinction is one of the five most catastrophic in Phanerozoic Earth history. Here we report carbon isotope evidence of a pronounced productivity collapse at the boundary, coincident with a sudden extinction among marine plankton, from stratigraphic sections on the Queen Charlotte Islands, British Columbia, Canada. This signal is similar to (though smaller than) the carbon isotope excursions associated with the Permian-Triassic and Cretaceous-Tertiary events., The Triassic-Jurassic (T-J) boundary mass extinction, one of the five most severe in Phanerozoic history, led to the demise of as many as 80% of all living species (1-3). Unanswered [...]

Comparing the timing of mass extinctions with the formation age of large igneous provinces reveals a close correspondence in five cases, but previous claims that all such provinces coincide with extinction events are unduly optimistic. The best correlation occurs for four consecutive mid-Phanerozoic examples, namely the end-Guadalupian extinction/Emeishan flood basalts, the end-Permian extinction/Siberian Traps, the end-Triassic extinction/central Atlantic volcanism and the early Toarcian extinction/Karoo Traps. Curiously, the onset of eruptions slightly post-dates the main phase of extinctions in these examples. Of the seven post-Karoo provinces, only the Deccan Traps coincide with a mass extinction, but in this case, the nature of the biotic crisis is best reconciled with the effects of a major bolide impact. Intraoceanic volcanism may also be implicated in a relatively minor end-Cenomanian extinction crisis, although once again the main phase of volcanism occurs after the crisis. The link between large igneous province formation and extinctions remains enigmatic; volume of extrusives and extinction intensity are unrelated and neither is there any apparent relationship with the rapidity of province formation. Violence of eruptions (proportions of pyroclastics) also appears unimportant. Six out of 11 provinces coincide with episodes of global warming and marine anoxia/dysoxia, a relationship that suggests that volcanic [CO.sub.2] emissions may have an important effect on global climate. Conversely, there is little, if any, geological evidence for cooling associated with continental flood basalt eruptions suggesting little long-term impact of [SO.sub.2] emissions. Large carbon isotope excursions are associated with some extinction events and intervals of flood basalt eruption but these are too great to be accounted for by the release of volcanic [CO.sub.2] alone. Thus, voluminous volcanism may in some circumstances trigger calamitous global environmental changes (runaway greenhouses), perhaps by causing the dissociation of gas hydrates. The variable efficiency of global carbon sinks during volcanic episodes may be an important control on environmental effects and may explain why the eruption of some vast igneous provinces, such as the Parana-Etendeka Traps, have little perceptible climatic impact. [C] 2001 Elsevier Science B.V. All rights reserved. Keywords: mass extinctions; flood basalts; marine anoxia; global warming; runaway greenhouse

The Permian-Triassic transition in the Karoo Basin of South Africa was characterized by a rapid and apparently basin-wide change from meandering to braided river systems, as evidenced by preserved sedimentary facies. This radical changeover in river morphology is consistent with geomorphic consequences stemming from a rapid and major die-off of rooted plant life in the basin. Evidence from correlative nonmarine strata elsewhere in the world containing fluvial Permian-Triassic boundary sections suggests that a catastrophic terrestrial die-off of vegetation was a global event, producing a marked increase in sediment yield as well as contributing to the global Δ[sup.13]C excursion across the Permian-Triassic boundary., The Permian-Triassic (P-T) mass extinction killed more than 90% of marine species and about 70% of terrestrial vertebrate families (1). Several causes for the P-T extinction have been proposed, including [...]

There was no hiding from the greatest mass extinction of all time. Two hundred and fifty million years ago, at the end of the Permian period and the opening of [...]

Episodes combining climatic warmth, massive volcanic eruptions, oceanic anoxia, and bursts of methane may lie behind major extinctions Massive extinctions involving many or most existing species, although not much fun [...]

There have been five major mass extinctions among the marine biota during the ~0.6 b.y. history of metazoan life on Earth. These mass extinctions have been ranked from the largest to the smallest by the severity of taxonomic diversity losses, but they have not been ranked by the severity of the ecologic changes that they produced. Here we utilize a system of paleoecological levels that allows for the ranking of ecological degradation or shifts associated with significant taxonomic events, along with an analysis of large-scale paleoenvironmental patterns of two of the great evolutionary faunas, to compare the relative ecologic degradation caused by two major mass extinctions. The Late Ordovician and Late Devonian mass extinctions produced similar taxonomic losses (marine families declined ~22% and 21%, respectively). However, our analyses show that whereas the Late Ordovician extinction resulted in only minimal permanent ecological change, the Late Devonian extinction resulted in the complete restructuring of many components of the marine ecosystem. Thus, the large-scale taxonomic and ecological significance of these extinction events are decoupled, implying that some taxa are ecologically more critical than others. Keywords: paleoecological levels, Devonian mass extinction, Ordovician mass extinction.

The end-Triassic marks one of the five biggest mass extinctions, but current geologic time scales are inadequate for understanding its dynamics. A tuff layer in marine sedimentary rocks encompassing the Triassic-Jurassic transition yielded a U-Pb zircon age of 199.6 [+ or -] 0.3 Ma. The dated level is immediately below a prominent change in radiolarian faunas and the last occurrence of conodonts. Additional recently obtained U-Pb ages integrated with ammonoid biochronology confirm that the Triassic Period ended ca. 200 Ma, several million years later than suggested by previous time scales. Published dating of continental sections suggests that the extinction peak of terrestrial plants and vertebrates occurred before 200.6 Ma. The end-Triassic biotic crisis on land therefore appears to have preceded that in the sea by at least several hundred thousand years. Keywords: mass extinction, U-Pb geochronology, biostratigraphy, Triassic-Jurassic boundary, Queen Charlotte Islands.

The Pliensbachian-Toarcian bivalve mass extinction in the Andean Basin of South America is characterized by a sharp drop in species diversity, caused mainly by extinction of endemics, and an extended lag phase. Whilst analysis of community attributes such as guild diversity, number of associations, and species richness of samples constituting associations did not yield any significant changes across the critical interval, rates of origination and extinction of species differed markedly between the various substages of the Early Jurassic. The most prominent feature is the drastic increase in the rate of origination of endemics culminating in the Early Pliensbachian. The time span between the peaks of rate of origination and extinction (5.7 Ma) closely corresponds to the longevity peak of Jurassic endemic bivalves (4-6 Ma). In addition to physico-chemical changes, we therefore explain the drop in species diversity as a result of the evolutionary dynamics of endemics, characterized by a preceding increase in the origination rate. Global mass extinctions are usually explained by one or more physico-chemical causes. We suggest that evolutionary factors, in particular species longevities, may substantially contribute to the phenomenon. Keywords: Jurassic, mass extinctions, communities, species diversity, evolution.

A combination of data from litho- and biofacies and gamma-ray spectrometry indicates an upward marine shallowing in the late Rhaetian succession of Nevada followed by deepening in the early Hettangian, which conforms well to a regression-transgression couplet of the sort associated with many marine mass extinctions. This pattern can be discerned widely across the world, most notably in North and South America and in Europe, suggesting the operation of eustatic control of sea level, a global fall being followed by a rise. Keywords: Triassic, Jurassic, transgression, regression, mass extinctions.

Conservations predict massive extinctions as a result of habitat loss. Habitat loss undoubtedly does drive extinctions, but dealing with an unmet assumption that underlies these predictions yields lower estimates. See [...]

Conservationists predict massive extinctions as a result of habitat loss. Habitat loss undoubtedly does drive extinctions, but dealing with an unmet assumption that underlies these predictions yields much lower estimates. See Letter(https://www.nature.com/articles/nature09985) Getting a handle on extinction rates There is broad agreement that Earth is facing a biodiversity crisis, but estimating extinction rates remains a daunting task, not least because it is almost impossible to determine when the very last individual of a species has died. Fangliang He and Stephen Hubbell demonstrate that a widely used indirect method of estimating extinction rates -- based on backward extrapolation of species-area relationship data -- tends to overestimate the problem. As an example, they cite data on passerine bird species in the United States. He and Hubbell stress that habitat loss remains a real and growing threat to biodiversity, although we need to develop more reliable means of monitoring the situation., Author(s): Carsten Rahbek [sup.1] , Robert K. Colwell [sup.2] Author Affiliations: (1) Department of Biology, Carsten Rahbek is at the Center for Macroecology, Climate and Evolution, University of Copenhagen, DK-2100 [...]

A study suggests that periodic changes in Earth's orbit, tilt and its wobble about its axis may be linked to appearance and extinction of mammalian species. Research on rodent teeth fossils buried in a layered sequence of rocks in Spain that spanned 22 million years reveal 132 evolutionary lineages, corresponding to varying cycles of orbit, tilt and wobble of the Earth.

A series of Permian/Triassic (P/T) mass extinctions eliminated nearly 90 percent of all life on the planet about 250 million years ago. New and better evidence is rapidly accumulating, resulting in a much better understanding of what caused the Permian extinction. The evidence is manifold, showing climatic and oceanic changes that were coincident with flood volcanism.

When, at least 12,000 years ago, human beings first crossed into North America from Siberia, the continent teemed with large animals. Today, of course, our only encounters with giant short-faced [...]

The debate continues over the period of the Great Dying, the largest of all mass extinctions in living organisms, which occurred 250 million years ago. Scientists have developed many ideas about what set off the large extinction event at the boundary between the Permian and Triassic ages, including large-scale volcanism in Siberia, development of oxygen-depleted oceans, changes in sea level or a combination of these incidents.

The extinction of planktonic foraminiferal species across the Cretaceous/Tertiary (K/T) boundary has been examined in continental-shelf sections at El Kef, Tunisia, and Brazos River, Texas. These sections are considered to contain the most complete boundary transition record known to date. In both sections, an extended period of species extinctions spans from about 300,000 yr below to about 200,000-300,000 yr above the K/T boundary. Distinct episodes of accelerated extinctions occur below the boundary and about 50,000 yr above the boundary. At El Kef, only 26% of the species extinctions appear directly associated with the K/T boundary and iridium anomaly. At Brazos River, no species extinctions or measurable faunal changes appear directly associated with the K/T boundary and iridium anomaly. Species extinctions selectively affect large, ornate, tropical to subtropical species first and small, primitive, nonornate, subtropical to temperate species last. This pattern of species extinction is likely caused by increased ecological stresses as a result of a late Maastrichtian sea-level regression and global cooling. The extended period of species extinctions and absence of extinctions at the K/T boundary at Brazos River is not entirely compatible with either impact or volcanism theories. Perhaps, multiple unrelated causes should be considered, including a sea-level regression, global cooling, a K/T boundary impact of limited extent, and extensive volcanism.

The case for periodicity in extinction, with a mass extinction every 26 x [10.sup.6] yr since the mid-Permian, rests on analyses of the fossil record of marine families and genera. We have checked the echinoderm and fish family extinctions which make up [is nearly equal] 20% of the data, and find that only 25% of our sample is signal (extinctions of monophyletic groups correctly dated to stage). The 75% noise component includes pseudoextinctions of non-monophyletic groups, and spurious data from other sources. The signal/noise ratio is virtually the same in echinoderms and fishes. Conspicuous peaks in our total family data correspond to five of the eight periodic extinction peaks that have been identified, but these five peaks are a feature of the noise component, not of the signal. We have also checked a randomly selected 20% of the generic extinctions in echinoderms and fishes since the Permian. The proportion of our data reflecting plausible extinctions is much lower among genera (31%) than among families (47%), whereas the proportion that samples peaks of fossilization rather than of extinction is much higher among genera (32%) than among families (16%). As with our families, peaks corresponding to periodic extinctions are restricted to the noise component of the generic data, but here the signal component is too small to bear much significance. We question the expectation that studies of global extinction will be more reliable the lower the taxonomic level investigated.

The appeal of a simple, extrinsic (sensu Gould 1977) physical mechanism for all or even one mass extinction is undeniable. But it now seems unlikely that extraterrestrial impacts provide the ultimate cause of more than a single mass extinction. At the Cretaceous-Tertiary (K-T) boundary there is ample evidence for unusual astrophysical or geophysical events, but the link between those events and the extinction of terrestrial and marine faunas and floras remains uncertain. One means of understanding the demise of clades during the K-T and other mass extinctions lies in the paleoecology of the survivors compared to casualties, in temporal, geographical, and ecological patterns. Likewise, similarities in patterns provide a means to test mechanisms common among extinction events (Jablonski 1986a). Extinctions are biological events. Evidence for extrinsic influences on the biosphere will certainly aid in comprehending the nature of biohistorical events, such as mass extinctions, and may well be responsible for those events, but the ecology of fossils is the crucial link to understanding these events.

Environmental change, including changes in biogeochemical cycles, climate, and sea level, is the primary cause of extinctions that result from mechanisms external to evolutionary dynamics. Evidence that extraordinary tectonism, including volcanism, sea-floor spreading, and eustatic sea level changes, took place prior to and at the Cretaceous-Tertiary boundary (K-TB) is sufficient to account for the environmental changes that led to mass extinctions. A coincident impact of an extraterrestrial object cannot be conclusively ruled out. Some mineralogic evidence suggests a scenario that includes impacts, but this does not rule out tectonism. The K-TB is certainly the best studied and most often discussed extinction boundary, but study of other extinction episodes and other potential extinction causes will now shed more light on mechanisms than continued study of the K-TB.