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    Marine anoxia as a trigger for the largest Phanerozoic positive carbon isotope excursion: Evidence from carbonate barium isotope record
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    The modern loss of species diversity has been labelled the 'sixth extinction' subsequent to the five major mass extinctions widely recognised in the Phanerozoic geologic record – the end-Ordovician (443.8 Ma), the Late Devonian (372.2 Ma), end-Permian (251.9 Ma), end-Triassic (201.4 Ma) and end-Cretaceous (66 Ma) events. Rankings in terms of numbers of genera suffering extinction, and especially in terms of ecological impact, however, put the end-Guadalupian (end-Capitanian) (259.8 Ma) extinction event in the same category with the other major mass extinctions. Thus, there were apparently six major Phanerozoic mass extinctions, and the current loss of species should perhaps be called the 'seventh extinction'.
    Extinction (optical mineralogy)
    Devonian
    Late Devonian extinction
    Permian–Triassic extinction event
    The recognition in 1980 of a signature of an extraterrestrial impact at the Cretaceous-Tertiary boundary and its apparent involvement with the mass extinction generated considerable enthusiasm for impacts at other mass extinctions. Numerous claims of impact evidence for the Permo-Triassic mass extinction (251.6 Ma), the largest of the Phanerozoic mass extinctions, have generally been rejected, found wanting, or been difficult to reproduce. Despite this lack of repeatable support, considerable available evidence is consistent with an impact, including the rapidity of extinction, coincident carbon shift, and evident correlation between terrestrial and marine extinctions. However attractive the hypothesis, the coincidence with the Siberian flood basalts and the complex nature of the carbon shift are in conflict with an impact. The most intriguing possibility is that the greatest mass extinction of the Phanerozoic left signals very similar to the end-Cretaceous mass extinction but was produced by entirely Earth-bound processes. If true, this would tell us far more about the nature of ecosystems and how they fail than would identification of another impact.
    Flood basalt
    Extinction (optical mineralogy)
    Extraterrestrial Life
    Macroevolution
    Citations (29)
    Abstract In the Phanerozoic, there are three major geological boundaries: Precambrian / Cambrian, Permian / Triassic and Cretaceous / Tertiary. Studies of these boundaries in China and over the world strongly suggest that they have the following similar features: mass extinctions of many, taxa, positive anomalies of platinum‐group metals, and abrupt changes of stable isotopes (δ 13 C). It is quite probable that these were the consequences of some rare catastrophic events of extraterrestrial origin. Hence, the three above‐mentioned mass extinction events may be regarded as key indicators for the division of the geological history of the Phanerozoic.
    Extraterrestrial Life
    Permian–Triassic extinction event
    Geologic time scale
    Extinction (optical mineralogy)
    Abstract The second largest Phanerozoic mass extinction occurred at the Ordovician-Silurian (O-S) boundary. However, unlike the other major mass extinction events, the driver for the O-S extinction remains uncertain. The abundance of mercury (Hg) and total organic carbon (TOC) of Ordovician and early Silurian marine sediments were analyzed from four sections (Huanghuachang, Chenjiahe, Wangjiawan and Dingjiapo) in the Yichang area, South China, as a test for evidence of massive volcanism associated with the O-S event. Our results indicate the Hg concentrations generally vary in parallel with TOC, and that the Hg/TOC ratios remain low and steady state through the Early and Middle Ordovician. However, Hg concentrations and the Hg/TOC ratio increased rapidly in the Late Katian, and have a second peak during the Late Hirnantian (Late Ordovician) that was temporally coincident with two main pulses of mass extinction. Hg isotope data display little to no variation associated with the Hg spikes during the extinction intervals, indicating that the observed Hg spikes are from a volcanic source. These results suggest intense volcanism occurred during the Late Ordovician, and as in other Phanerozoic extinctions, likely played an important role in the O-S event.
    Extinction (optical mineralogy)
    Baltica
    Mercury
    Citations (94)
    Extinction (optical mineralogy)
    Permian–Triassic extinction event
    Devonian
    Late Devonian extinction
    Mass extinction is characterized by the loss of more than 50 percent of the world's species within a short interval of geologic time - months to as much as 3 million years (My). In the fossil record, these events have primarily been recorded from the marine realm. Three patterns of mass extinction have been described - catastrophic, stepwise, and graded extinction. Many well-studied extinction intervals contain elements of more than one pattern, suggesting that these biotic crises were caused by varied forcing mechanisms linked by complex environmental feedback loops. This hypothesis is supported by the discovery that the four well-studied Phanerozoic mass extinctions (Late Devonian, middle and terminal Cretaceous, Eocene-Oligocene boundary extinctions) share a number of physical, chemical, and biological characteristics in common. They consistently show stepwise extinction patterns linked to intervals of extraordinary fluctuations in the temperature, chemistry and structure of ocean-climate systems, at rates and magnitudes well above background levels. In addition, tropical ecosystems were the first and most severely affected, and more poleward, temperate biotas were mainly stressed during the later phases of the extinction interval. Evidence for these unusual environmental changes is derived from high-resolution (cm-scale) paleobiological, sedimentological, trace-element and stable-isotope analyses spanning mass extinction intervals. These dramatic environmental fluctuations were the immediate causes of mass extinction, as they progressively exceeded the survival limits of global biotas largely adapted to warm, equable, ice-free climates which characterized over 90 percent of Phanerozoic time. These environmental fluctuations probably represented feedback phenomena from more powerful, short-term forcing mechanisms which abruptly perturbed the structure of ocean-climate systems. Multiple impacts of extraterrestrial objects within short (<1-3 My) time intervals - so-called meteorite/comet showers - are the most logical candidates. This hypothesis is supported by physical and chemical evidence for impacts clustered around most, but not all, Mesozoic and Cenozoic mass extinctions.
    Extinction (optical mineralogy)
    Late Devonian extinction
    Permian–Triassic extinction event
    Geologic record
    Citations (3)
    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.
    Extinction (optical mineralogy)
    Abstract Climate change is a critical factor affecting biodiversity. However, the quantitative relationship between temperature change and extinction is unclear. Here, we analyze magnitudes and rates of temperature change and extinction rates of marine fossils through the past 450 million years (Myr). The results show that both the rate and magnitude of temperature change are significantly positively correlated with the extinction rate of marine animals. Major mass extinctions in the Phanerozoic can be linked to thresholds in climate change (warming or cooling) that equate to magnitudes >5.2 °C and rates >10 °C/Myr. The significant relationship between temperature change and extinction still exists when we exclude the five largest mass extinctions of the Phanerozoic. Our findings predict that a temperature increase of 5.2 °C above the pre-industrial level at present rates of increase would likely result in mass extinction comparable to that of the major Phanerozoic events, even without other, non-climatic anthropogenic impacts.
    Extinction (optical mineralogy)
    Citations (105)
    The Kalkarindji continental flood basalt province of Northern Australia is the oldest basaltic LIP in the Phanerozoic having erupted in the mid-Cambrian. At this time, during the Cambrian Explosion, the global environment suffered a series of mass extinctions and biotic turnover. Kalkarindji had the potential to release 1.65 x 106 Tg of CO2, approximately 1.72% of the total Cambrian atmospheric carbon reservoir. It has therefore been implicated as a driver of the environmental changes in the Cambrian Series 2. However, temporal discrepancies between Kalkarindji eruptions and biotic turnover may prevent this LIP from being attributed as the sole cause of the Botomian-Toyonian Extinction, which wiped out up to 45% of all genera in the fossil record; while environmental factors such as sea-level change causing ocean anoxia are implicated in the Redlichiid-Olenellid Extinction. It is certainly possible that Kalkarindji could have played a part in forcing these environmental changes, but further advances in geochronology and sedimentary volcanic proxies are needed to confidently define a direct causational link between these events at the dawn of the Phanerozoic.
    Flood basalt
    Environmental change
    Large igneous province
    Geologic record
    Extinction (optical mineralogy)