Several Palaeozoic mass extinction events during the Ordovician and Silurian periods (ca. 485 to 420 to million years ago) shaped the evolution of life on our planet. Although some of these short-lived, periodic events were responsible for eradication of up to 85% of marine species, the exact kill-mechanism responsible for these crises remains poorly understood.
An international team led by Thijs Vandenbroucke (researcher at the French CNRS and invited professor at UGent) and Poul Emsbo (US Geological Survey) initiated a study to investigate a little known association between 'teratological' or 'malformed' fossil plankton assemblages coincident with the initial stages of these extinction events.
In a paper just published in Nature Communications, they present evidence that malformed fossil remains of marine plankton from the late Silurian (415 million years ago) contain highly elevated concentrations of heavy metals, such as iron, lead, and arsenic. These are well-known toxins that cause morphologic abnormalities in modern aquatic organisms; which led the authors to conclude that metal poisoning caused the malformation observed in these ancient organisms and may have contributed to their extinction and that of many other species.
Severity of ocean acidification following the end-Cretaceous asteroid impact
Authors:
Tyrrell et al
Abstract:
Most paleo-episodes of ocean acidification (OA) were either too slow or too small to be instructive in predicting near-future impacts. The end-Cretaceous event (66 Mya) is intriguing in this regard, both because of its rapid onset and also because many pelagic calcifying species (including 100% of ammonites and more than 90% of calcareous nannoplankton and foraminifera) went extinct at this time. Here we evaluate whether extinction-level OA could feasibly have been produced by the asteroid impact. Carbon cycle box models were used to estimate OA consequences of (i) vaporization of up to 60 × 1015 mol of sulfur from gypsum rocks at the point of impact; (ii) generation of up to 5 × 1015 mol of NOx by the impact pressure wave and other sources; (iii) release of up to 6,500 Pg C as CO2 from vaporization of carbonate rocks, wildfires, and soil carbon decay; and (iv) ocean overturn bringing high-CO2 water to the surface. We find that the acidification produced by most processes is too weak to explain calcifier extinctions. Sulfuric acid additions could have made the surface ocean extremely undersaturated (Ωcalcite less than 0.5), but only if they reached the ocean very rapidly (over a few days) and if the quantity added was at the top end of literature estimates. We therefore conclude that severe ocean acidification might have been, but most likely was not, responsible for the great extinctions of planktonic calcifiers and ammonites at the end of the Cretaceous.
Ocean acidification and the Permo-Triassic mass extinction
Authors:
Clarkson et al
Abstract:
Ocean acidification triggered by Siberian Trap volcanism was a possible kill mechanism for the Permo-Triassic Boundary mass extinction, but direct evidence for an acidification event is lacking. We present a high-resolution seawater pH record across this interval, using boron isotope data combined with a quantitative modeling approach. In the latest Permian, increased ocean alkalinity primed the Earth system with a low level of atmospheric CO2 and a high ocean buffering capacity. The first phase of extinction was coincident with a slow injection of carbon into the atmosphere, and ocean pH remained stable. During the second extinction pulse, however, a rapid and large injection of carbon caused an abrupt acidification event that drove the preferential loss of heavily calcified marine biota.
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Nano particles as the primary cause for long-term sunlight suppression at high southern latitudes following the Chicxulub impact – evidence from ejecta deposits in Belize and Mexico
Authors:
Vajda et al
Abstract:
Life on Earth was sharply disrupted 66 million years ago as an asteroid hit the sea-floor in what is today Yucatan Peninsula, Mexico. Approximately 600 km3 of sedimentary rock were vaporized, ejected into the atmosphere and subsequently deposited globally as an ejecta apron and fallout layer. Proximal ejecta deposits occur in Belize and southern Mexico where the so called Albion island spheroid bed' is superimposed on the target rock (the Barton Creek Formation). We analyzed the spheroid bed via Mössbauer spectroscopy, petrology, XRD, and palynology at several sites ~ 350–500 km distance from the crater centre. Our results show that the relative concentrations of Fe in nano-phase goethite (α-FeOOH) are very high in the spheroid bed samples from Albion Island (Belize) and from Ramonal South (Mexico), but are low to absent in the spheroid bed at Ramonal North, and in the Cretaceous target rock. Moreover, our study shows that goethite and haematite are the dominant Fe-oxide nano-phases and the XRD results show that the target rock consists of both calcite and dolomite. We suggest that the heterogeneous composition of the spheroid bed between the various sites reflects the different types of target rocks that were dispersed within the rapidly expanding vapour plume and the complex sorting processes involved in the formation of the ejecta blanket. The distribution of the vaporized target rock strongly influenced life on Earth at the close of the Mesozoic. However, the comparatively thin K–Pg boundary clay in high-latitude Gondwanan successions combined with evidence of catastrophic changes to the biota in this region implies that the long-term sunlight suppression in the Southern Hemisphere was mainly governed by the large quantities of hydrous aerosols nucleated around sulphuric acid droplets or nano-sized particles, such as the nano-phase Fe-oxides.
Extinction patterns among bivalves in South China during the Permian-Triassic crisis
Authors:
Huang et al
Abstract:
Late Permian Changhsingian bivalves in South China are very abundant and diverse in nearshore, inner shelf, outer shelf, and deep basin facies. All reported data of both bivalve genera and species from the Permian-Triassic boundary strata of South China have been systematically collected and studied for understanding the evolutionary process of various bivalve groups in different environments through the great Permian-Triassic transition. At the genus level, bivalves show an extinction rate of 50% in the first phase of the Permian-Triassic crisis, though only 9.1% in the second phase. There appears to be no selection of extinction in life-style, feeding type or habitat among bivalves from South China through the crisis. There is no significant difference in the extinction rates between epifaunal and infaunal bivalve genera in all environments. Suspension feeders showed moderate extinction rates, while no deposit feeders went extinct at the genus level. In addition, infaunal bivalves were not at more risk of extinction than epifaunal forms. A combination of ocean anoxia and high seawater temperatures might have contributed to the mass extinction among bivalves during the Permian-Triassic crisis.
