The hyperthermals of the geological record

During the last 540 million years five mass extinction events shaped the history of the Earth. Those events were related to extreme climatic changes. The geological records show that large and rapid global warming events occurred repeatedly during the course of Earth history.
Our planet’s climate has oscillated between two basic states: the “Icehouse”, and the “Greenhouse”, and superimposed on this icehouse–greenhouse climate cycling, there are a number of geologically abrupt events known as hyperthermals, when atmospheric CO2 concentrations may rise above 16 times (4,800 ppmv). Although each hyperthermal is unique, they are consequence from the release of anomalously large inputs of CO2 into the atmosphere and are relatively short-lived (with the exception of the Permian–Triassic boundary).

A summary of the most significant hyperthermals in the last 300 Myr. From Foster et. al., 2018.

The emplacement of large igneous provinces (LIPs) is commonly associated with hyperthermals, for example, the Siberian Traps at the P–T boundary. The CO2 emissions caused global warming. The SO2 emissions on mixing with water vapour in the atmosphere, caused acid rain, which in turn killed land plants and caused soil erosion. Warmer oceans melted frozen methane located in marine sediments which pushed the global temperatures to higher levels. Additionally, the increased continental weathering induced by acid rain and global warming led to increased marine productivity and eutrophication, and so oceanic anoxia, and marine mass extinctions.

The hyperthermal at the P–T boundary was associated with the most severe terrestrial and oceanic mass extinction of the last 541 Myr, where 96% of species became extinct. It comprises two killing events, one at the end of the Permian (EPME) and a second at the beginning of the Triassic, separated by 60000 years. In terms of carbon isotope excursion, the P–T boundary hyperthermal and the PETM share many similarities, but the warming after the P-T boundary was more extreme and extended for longer than PETM.

Flow chart summarizing proposed cause-and-effect relationships during the end-Permian extinction (From Bond and Wignall, 2014)

The End-Triassic Extinction is probably the least understood of the big five. It has been linked to the eruption of the Central Atlantic Magmatic Province (CAMP), a large igneous province emplaced during the initial rifting of Pangea. Most mammal-like reptiles and large amphibians disappeared, as well as early dinosaur groups. In the oceans, this event eliminated conodonts and nearly annihilated corals, ammonites, brachiopods and bivalves. In the Southern Hemisphere, the vegetation turnover consisted in the replacement to Alisporites (corystosperm)-dominated assemblage to a Classopollis (cheirolepidiacean)-dominated one.

The early Toarcian Oceanic Anoxic Event (T-OAE; ∼183 mya) in the Jurassic Period is considered as one of the most severe of the Mesozoic era. The T-OAE is thought to have been caused by increased atmospheric CO2 triggered by Karoo–Ferrar volcanism. Results from the Paris Bassin indicates that the increasing greenhouse conditions may have caused acidification in the oceans, hampering carbonate bio-mineralisation, and provoking a dramatical loss in the CO2 storage capacity of the oceans.

Tentative changes in mid-latitude vegetation patterns during OAE2. (a) Araucariaceae, (b) other conifers incl. Cheirolepidiaceae, (c) Cupressaceae, (d) angiosperms incl. Normapolles-producing forms, (e) ferns. From Heimhofer et al., 2018.

The early Aptian Oceanic Anoxic Event (OAE1a, 120 Ma) represents a geologically brief time interval characterized by rapid global warming, dramatic changes in ocean circulation including widespread oxygen deficiency, and profound changes in marine biotas. During the event, black shales were deposited in all the main ocean basins. It was also associated with the calcification crisis of the nannoconids, the most ubiquitous planktic calcifiers during the Early Cretaceous. Their near disappearance is one of the most significant events in the nannoplankton fossil record.

The mid-Cretaceous Oceanic Anoxic Event 2 (OAE2, 93 Ma) marks the onset of an extreme phase in ocean temperatures known as the “Cretaceous thermal maximum”. It has been postulated that the OAE2 was triggered by a massive magmatic episode.

Comparison of the effects of anthropogenic emissions (total of 5000 Pg C over 500 years) and PETM carbon release (3000 Pg C over 6 kyr) on the surface ocean saturation state of calcite. From Zeebe, 2013

The Paleocene-Eocene Thermal Maximum (PETM; 55.8 million years ago), was a short-lived (~ 200,000 years) global warming event attributed to a rapid rise in the concentration of greenhouse gases in the atmosphere. It was suggested that this warming was initiated by the melting of methane hydrates on the seafloor and permafrost at high latitudes. During the PETM, around 5 billion tons of CO2 was released into the atmosphere per year, and temperatures increased by 5 – 9°C. This event was accompanied by other large-scale changes in the climate system, for example, the patterns of atmospheric circulation, vapor transport, precipitation, intermediate and deep-sea circulation and a rise in global sea level. But unlike other hyperthermals, the PETM is not associated with significant extinctions.

Anthropogenic climate change and ocean acidification resulting from the emission of vast quantities of CO2 and other greenhouse gases pose a considerable threat to ecosystems and modern society. The combination of global warming and the release of large amounts of carbon to the ocean-atmosphere system during the PETM has encouraged analogies to be drawn with modern anthropogenic climate change. The current rate of the anthropogenic carbon input is probably greater than during the PETM, causing a more severe decline in ocean pH and saturation state. Also the biotic consequences of the PETM were fairly minor, while the current rate of species extinction is already 100–1000 times higher than would be considered natural. This underlines the urgency for immediate action on global carbon emission reductions.

References:

Foster GL, Hull P, Lunt DJ, Zachos JC. (2018) Placing our current‘hyperthermal’ in the context of rapid climate change in our geological past. Phil. Trans. R. Soc. A 376: 20170086 http://dx.doi.org/10.1098/rsta.2017.0086

Benton MJ. (2018) Hyperthermal-driven mass extinctions: killing models during the Permian–Triassic mass extinction. Phil. Trans. R. Soc. A 376: 20170076. http://dx.doi.org/10.1098/rsta.2017.0076

Penn, J. L., Deutsch, C., Payne, J. L., & Sperling, E. A. (2018). Temperature-dependent hypoxia explains biogeography and severity of end-Permian marine mass extinction. Science, 362(6419), eaat1327. doi:10.1126/science.aat1327 

Ernst, R. E., & Youbi, N. (2017). How Large Igneous Provinces affect global climate, sometimes cause mass extinctions, and represent natural markers in the geological record. Palaeogeography, Palaeoclimatology, Palaeoecology, 478, 30–52. doi:10.1016/j.palaeo.2017.03.014

Turgeon, S. C., & Creaser, R. A. (2008). Cretaceous oceanic anoxic event 2 triggered by a massive magmatic episode. Nature, 454(7202), 323–326. doi:10.1038/nature07076

Ulrich Heimhofer, Nina Wucherpfennig, Thierry Adatte, Stefan Schouten, Elke Schneebeli-Hermann, Silvia Gardin, Gerta Keller, Sarah Kentsch & Ariane Kujau (2018) Vegetation response to exceptional global warmth during Oceanic Anoxic Event 2, Nature Communications volume 9, Article number: 3832

Zeebe RE and Zachos JC. 2013 Long-term legacy ofmassive carbon input to the Earth system: Anthropocene versus Eocene. Phil Trans R Soc A 371: 20120006. http://dx.doi.org/10.1098/rsta.2012.0006.

 

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A Tale of Two Exctintions.

The permian triassic boundary at Meishan, China (Photo: Shuzhong Shen)

The Permian Triassic boundary at Meishan, China (Photo: Shuzhong Shen)

Extinction is the ultimate fate of all species. The fossil record indicates that more than 95% of all species that ever lived are now extinct. Over the last 3 decades, mass extinction events  have become the subject of increasingly detailed and multidisciplinary investigations. In 1982, Jack Sepkoski and David M. Raup identified five major extinction events in Earth’s history: at the end of the Ordovician period, Late Devonian, End Permian, End Triassic and the End Cretaceous. These five events are know as the Big Five.

The end-Permian extinction is the most severe biotic crisis in the fossil record, with as much as 95% of the marine animal species and a similarly high proportion of terrestrial plants and animals going extinct . This great crisis occurred 252 million years ago (Ma) during an episode of global warming. The End-Triassic Extinction  is probably the least understood of the big five. Most mammal-like reptiles and large amphibians disappeared, as well as early dinosaur groups. In the oceans, this event eliminated conodonts and nearly annihilated corals, ammonites, brachiopods and bivalves. Although it’s almost impossible briefly summarize all the changes in biodiversity associated with both extinction events, we can describe their broad trends.

 

Flow chart summarizing proposed cause-and-effect relationships during the end-Permian extinction (From Bond and Wignall, 2014)

Flow chart summarizing proposed cause-and-effect relationships during the end-Permian extinction (From Bond and Wignall, 2014)

Both extinction events are commonly linked to the emplacement of the large igneous provinces of the Siberian Traps and the Central Atlantic Magmatic Province. Massive volcanic eruptions with lava flows, released large quantities of sulphur dioxide, carbon dioxide, thermogenic methane and large amounts of HF, HCl, halocarbons and toxic aromatics and heavy metals into the atmosphere. Furthermore, volcanism contribute gases to the atmosphere, such as Cl, F, and CH3Cl from coal combustion, that suppress ozone formation. Acid rain likely had an impact on freshwater ecosystems and may have triggered forest dieback. Mutagenesis observed in the Lower Triassic herbaceous lycopsid Isoetales has been attributed to increased levels of UV-radiation. Charcoal records point to forest fires as a common denominator during both events. Forest dieback was accompanied by the proliferation of opportunists and pioneers, including ferns and fern allies. Moreover, both events led to major schisms in the dominant terrestrial herbivores  and apex predators, including the late Permian extinction of the pariaeosaurs and many dicynodonts and the end-Triassic loss of crurotarsans (van de Schootbrugge and Wignall, 2016).

Aberrant pollen and spores from the end-Triassic extinction interval (scale bars are 20 μm). (a) Ricciisporites tuberculatus from the uppermost Rhaetian deposits at Northern Ireland (adapted from van de Schootbrugge and Wignall, 2016)

Aberrant pollen and spores from the end-Triassic extinction interval (scale bars are 20 μm). (a) Ricciisporites
tuberculatus and b) Kraeuselisporites reissingerii (adapted from van de Schootbrugge and Wignall, 2016)

During the end-Permian Event, the woody gymnosperm vegetation (cordaitaleans and glossopterids) were replaced by spore-producing plants (mainly lycophytes) before the typical Mesozoic woody vegetation evolved. The palynological record suggests that wooded terrestrial ecosystems took four to five million years to reform stable ecosystems, while spore-producing lycopsids had an important ecological role in the post-extinction interval. A key factor for plant resilience is the time-scale: if the duration of the ecological disruption did not exceed that of the viability of seeds and spores, those plant taxa have the potential to recover (Traverse, 1988). Palynological records from across Europe provide evidence for complete loss of tree-bearing vegetation reflected in a strong decline in pollen abundance at the end of the Triassic. In the Southern Hemisphere, the vegetation turnover consisted in the replacement to Alisporites (corystosperm)-dominated assemblage to a Classopollis (cheirolepidiacean)-dominated one.

Comparison of extinction rates for calcareous organisms during the end-Permian and end-Triassic extinction event (from van de Schootbrugge and Wignall, 2016)

Comparison of extinction rates for calcareous organisms during the end-Permian and end-Triassic extinction event (from van de Schootbrugge and Wignall, 2016)

Rapid additions of carbon dioxide during extreme events may have driven surface waters to undersaturation. Acidification affects the biogeochemical dynamics of calcium carbonate, organic carbon, nitrogen, and phosphorus in the ocean and interferes with a range of processes, including growth, calcification, development, reproduction and behaviour in a wide range of marine organisms like foraminifera, planktonic coccolithophores, pteropods and other molluscs,  echinoderms, corals, and coralline algae. Both extinction events led to near-annihilation of cnidarian clades and other taxa responsible for reef construction, resulting in ‘reef gaps’ that lasted millions of years. Black shales deposited across both extinction events also contain increased concentrations of the biomarker isorenieratane, a pigment from green sulphur bacteria, suggesting that the photic zone underwent prolonged periods of high concentrations of hydrogen sulphide. Following the end-Triassic extinction, Early Jurassic shallow seas witnessed recurrent euxinia over a time span of 25 million years, culminating in the Toarcian Oceanic Anoxic Event.

 

References:

BAS VAN DE SCHOOTBRUGGE and PAUL B. WIGNALL (2016). A tale of two extinctions: converging end-Permian and end-Triassic scenarios. Geological Magazine, 153, pp 332-354. doi:10.1017/S0016756815000643.

BACHAN, A. & PAYNE, J. L. 2015. Modelling the impact of pulsed CAMP volcanism on pCO2 and δ13C across the Triassic-Jurassic transition. Geological Magazine, published online

Retallack, G.J. 2013. Permian and Triassic greenhouse crises. Gondwana Research 24:90–103.

 

A palaeobotanical perspective on the Permian extinction.

 

Leaf bank of Glossopteris leaves (Adapted from Mcloughlin, 2012)

Leaf bank of Glossopteris leaves (Adapted from Mcloughlin, 2012)

The fossil record indicates that more than 95% of all species that ever lived are now extinct. Occasionally, extinction events reach a global scale with many species of all ecological types dying out in a near geological instant. These are mass extinctions. They were originally identified in the marine fossil record and have been interpreted as a result of catastrophic events or major environmental changes that occurred too rapidly for organisms to adapt. Mass extinctions are probably due to a set of different possible causes like basaltic super-eruptions, impacts of asteroids, global climate changes, or continental drift. A central question in the understanding of mass extinctions is whether the extinction was a sudden or gradual event. This question may be addressed by examining the pattern of last occurrences of fossil species in a stratigraphic section.

Jack Sepkoski and David M. Raup identified five major extinction events in Earth’s history: at the end of the Ordovician period, Late Devonian, End Permian, End Triassic and the End Cretaceous. The most recently identified mass extinction occurred during the Middle Permian, about  262 million years ago, and it was first recognised in the marine realm as a turnover among foraminifera, with fusulinaceans among the principal casualties.

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Total diversity patterns of continental diversity (solid line) and marine diversity (dotted line) at the family level. Arrows indicate the mass extinction events. (From Cascales-Miñana and Cleal 2015)

Extinction dynamics in the marine and terrestrial biotas followed different trajectories, and only the Permo-Triassic event coincided with a clear and abrupt diminution of both realms. Moreover, analysis of the paleobotanical record has suggested that plants may have suffered an additional extinction event, that is not reflected significantly in the marine realm, at the Carboniferous–Permian boundary. Evidence also suggests that  terrestrial environments suffered a single global pulse of extinction in the latest Permian, affecting both the fauna and flora (Cascales-Miñana and Cleal 2015).

During the end-Permian Event, the woody gymnosperm vegetation (cordaitaleans and glossopterids) were replaced by spore-producing plants (mainly lycophytes) before the typical Mesozoic woody vegetation evolved. The palynological record suggests that wooded terrestrial ecosystems took four to five million years to reform stable ecosystems, while spore-producing lycopsids had an important ecological role in the post-extinction interval. A key factor for plant resilience is the time-scale: if the duration of the ecological disruption did not exceed that of the viability of seeds and spores, those plant taxa have the potential to recover (Traverse, 1988).

 

References:

Borja Cascales-Miñana, José B. Diez, Philippe Gerrienne & Christopher J.Cleal (2015): A palaeobotanical perspective on the great end-Permian biotic crisis, HistoricalBiology, DOI: 10.1080/08912963.2015.1103237

Aberhan M. 2014. Mass extinctions: ecological diversity maintained. NatGeosci. 7:171–172.

Cascales-Miñana B, Cleal CJ. 2014. The plant fossil record reflects just two great extinction events. Terra Nova. 26(3):195–200.

The Middle Permian mass extinction.

The Kapp Starostin Formation, Festningen section, Spitsbergen. The uppermost of the 3 yellow limestone beds records the Middle Permian mass extinction (Credit: Photographer: Dierk Blomeier. For David P.G. Bond and colleagues, GSA Bulletin, 2015.)

The Kapp Starostin Formation, Festningen section, Spitsbergen. The uppermost of the 3 yellow limestone beds records the Middle Permian mass extinction (Photo Credit: Dierk Blomeier. For David P.G. Bond and colleagues, GSA Bulletin, 2015.)

Extinction is the ultimate fate of all species. The fossil record indicates that more than 95% of all species that ever lived are now extinct. Individuals better adapted to environments are more likely to survive and when a species does fail, it is called a background extinction. Occasionally extinction events reach a global scale, with many species of all ecological types dying out in a near geological instant. These are mass extinctions. They were originally identified in the marine fossil record and have been interpreted as a result of catastrophic events or major environmental changes that occurred too rapidly for organisms to adapt.  Mass extinctions are probably due to a set of different possible causes like basaltic super-eruptions, impacts of asteroids, global climate changes, or continental drift.

George Cuvier, the great French anatomist and paleontologist, was the first to suggested that periodic “revolutions” or catastrophes had befallen the Earth and wiped out a number of species. But under the influence of Lyell’s uniformitarianism, Cuvier’s ideas were rejected as “poor science”. The modern study of mass extinction did not begin until the middle of the twentieth century. One of the most popular of that time was “Revolutions in the history of life” written by Norman Newell in 1967.

The fossil record shows that biodiversity in the world has been increasing dramatically for 200 million years and is likely to continue. The two mass extinctions in that period (at 201 million and 66 million years ago) slowed the trend only temporarily. Genera are the next taxonomic level up from species and are easier to detect in fossils. The Phanerozoic is the 540-million-year period in which animal life has proliferated. Chart created by and courtesy of University of Chicago paleontologists J. John Sepkoski, Jr. and David M. Raup.

Biodiversity in the fossil record.  (From Wikimedia Commons)

Over the last 3 decades, mass extinction events  have become the subject of increasingly detailed and multidisciplinary investigations. In 1982, Jack Sepkoski and David M. Raup used a simple form of time series analysis at the rank of family to distinguish between background extinction levels and mass extinctions in marine faunas, and identified five major extinction events in Earth’s history: at the end of the Ordovician period, Late Devonian, End Permian, End Triassic and the End Cretaceous. These five events are know as the Big Five. The most recently identified mass extinction occurred during the Middle Permian, about  262 million years ago, and it was first recognised in the marine realm as a turnover among foraminifera, with fusulinaceans among the principal casualties. The crisis also affected numerous other shallow-marine taxa, including corals, bryozoans, brachiopods, bivalves and ammonoids. Until now, all detailed studies have focused on equatorial sections, especially those of South China. That extinction coincide with the Emeishan large igneous province. But, new data indicates that at the same time there was two severe extinctions amongst brachiopods in northern boreal latitudes in the Kapp Starostin Formation of Spitsbergen, an island roughly 890 km north of the Norwegian mainland.

Fusulinids from the Topeka Limestone  (Upper Carboniferous of Kansas, USA) From Wikimedia Commons

Fusulinids from the Topeka Limestone (Upper Carboniferous of Kansas, USA) From Wikimedia Commons

The Kapp Starostin Formation contains cool-water boreal faunas that include abundant siliceous sponges, brachiopods, and bryozoans. The widespread and near-total loss of carbonates across the Boreal Realm also suggests a role for acidification in the crisis.  This extinction predates the end-Permian mass extinction, because a subsequent recovery of brachiopods and especially bivalves is seen in the Late Permian. This post-extinction fauna disappears 10 m below the top of the Kapp Starostin Formation and thus fails to survive until the end of the Permian (Bond et al., 2015). This is a true mass extinction because the new data suggest that about 50 per cent of all marine species died during the event.

Oceanic oxygen depletion represents a potent cause of extinction in marine settings, and is often linked with volcanic activity, warming, and transgression. However,  the role of anoxia in the wider Capitanian extinction scenario remains enigmatic. Volcanically induced effects are multiple and include acidification.

brachi

Brachiopods from the Kapp Starostin Formation (Image adapted from Bond et al., 2015)

Acidification affects the biogeochemical dynamics of calcium carbonate, organic carbon, nitrogen, and phosphorus in the ocean and interferes with a range of processes, including growth, calcification, development, reproduction and behaviour in a wide range of marine organisms like foraminifera, planktonic coccolithophores, pteropods and other molluscs,  echinoderms, corals, and coralline algae. Ocean acidification in the geological record, is often inferred from a decrease in the accumulation and preservation of CaCO3 in marine sediments, potentially indicated by an increased degree of fragmentation of foraminiferal shells. But, recently, a variety of trace-element and isotopic tools have become available to infer past seawater carbonate chemistry.

Undoubtedly, the proximity of the End Permian extinction, makes difficult to determine if these events are separate or are part of a the same event.

References:

David P.G. Bond, Paul B. Wignall, Michael M. Joachimski, Yadong Sun, Ivan Savov, Stephen E. Grasby, Benoit Beauchamp and Dierk P.G. Blomeier, 2015, An abrupt extinction in the Middle Permian (Capitanian) of the Boreal Realm (Spitsbergen) and its link to anoxia and acidification, Geological Society of America Bulletin, doi: 10.1130/B31216.1

Wignall, P.B., Bond, D.P.G., Kuwahara, K., Kakuwa, Y., Newton, R.J., and Poulton, S.W., 2010, An 80 million year oceanic redox history from Permian to Jurassic pelagic sediments of the Mino-Tamba terrane, SW Japan, and the origin of four mass extinctions: Global and Planetary Change, v. 71, p. 109–123, doi:10.1016/j.gloplacha .2010.01.022.

Wignall, P.B., Bond, D.P.G., Newton, R.J., Haas, J., Hips, K., Wang, W., Jiang, H.-S., Lai, X.-L., Sun, Y.-D., Altiner, D., Védrine, S., and Zajzon, N., 2012, The Capitanian (Middle Permian) mass extinction in western Tethys: A fossil, facies and δ13C study from Hungary and Hydra Island (Greece): Palaios, v. 27, p. 78–89, doi:10.2110/palo.2011.p11-058r.

Ocean acidification and the end-Permian mass extinction

 

Permian Seafloor Photograph by University of Michigan Exhibit Museum of Natural History.

Permian Seafloor
Photograph by University of Michigan Exhibit Museum of Natural History.

About one third of the carbon dioxide released by anthropogenic activity is absorbed by the oceans. But the CO2 uptake lowers the pH and alters the chemical balance of the oceans. This phenomenon is called ocean acidification, and is occurring at a rate faster than at any time in the last 300 million years (Gillings, 2014; Hönisch et al. 2012). Acidification affects the biogeochemical dynamics of calcium carbonate, organic carbon, nitrogen, and phosphorus in the ocean and interferes with a range of processes, including growth, calcification, development, reproduction and behaviour in a wide range of marine organisms like planktonic coccolithophores, foraminifera, pteropods and other molluscs,  echinoderms, corals, and coralline algae. Rapid additions of carbon dioxide during extreme events in Earth history, including the end-Permian mass extinction (252 million years ago) and the Paleocene-Eocene Thermal Maximum (PETM, 56 million years ago) may have driven surface waters to undersaturation.

Flow chart summarizing proposed cause-and-effect relationships during the end-Permian extinction (From Bond and Wignall, 2014)

Flow chart summarizing proposed cause-and-effect relationships during the end-Permian extinction (From Bond and Wignall, 2014)

The end-Permian extinction is the most severe biotic crisis in the fossil record, with as much as 95% of the marine animal species and a similarly high proportion of terrestrial plants and animals going extinct . This great crisis occurred about 252 million years ago (Ma) during an episode of global warming.  The cause or causes of the Permian extinction remain a mystery but new data indicates that the extinction had a duration of 60,000 years and may be linked to massive volcanic eruptions from the Siberian Traps. The same study found evidence that 10,000 years before the die-off, the ocean experienced a pulse of light carbon that most likely led to a spike of carbon dioxide in the atmosphere. Volcanism and coal burning also contribute gases to the atmosphere, such as Cl, F, and CH3Cl from coal combustion, that suppress ozone formation.

Image that shows field work in the United Arab Emirates. Credit: D. Astratti

Image that shows field work in the United Arab Emirates. Credit: D. Astratti

Ocean acidification in the geological record, is often inferred from a decrease in the accumulation and preservation of CaCO3 in marine sediments, potentially indicated by an increased degree of fragmentation of foraminiferal shells. But, recently, a variety of trace-element and isotopic tools have become available to infer past seawater carbonate chemistry. The boron isotope composition of carbonate samples obtained from a shallow-marine platform section at Wadi Bih on the Musandam Peninsula, United Arab Emirates, allowed to reconstruct seawater pH values and atmospheric pCO2 concentrations and obtain for the very first time, direct evidence of ocean acidification in the Permo-Triassic boundary. The evidence indicates that 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 (Clarkson et al, 2015).

The increasing evidence that the end-Permian mass extinction was precipitated by rapid release of CO2 into Earth’s atmosphere is a valuable reminder for an immediate action on global carbon emission reductions.

 

References:

Clarkson MO, Kasemann SA, Wood RA, Lenton TM, Daines SJ, Richoz S, Ohnemueller F, Meixner A, Poulton SW, Tipper ET. Ocean acidification and the Permo-Triassic mass extinction. Science, 2015 DOI: 10.1126/science.aaa0193

Feng, Q., Algeo, T.J., Evolution of oceanic redox conditions during the Permo-Triassic transition: Evidence from deepwater radiolarian facies, Earth-Sci. Rev. (2014), http://dx.doi.org/10.1016/j.earscirev.2013.12.003

Hönisch, A. Ridgwell, D. N. Schmidt, E. Thomas, S. J. Gibbs, A. Sluijs, R. Zeebe, L. Kump, R. C. Martindale, S. E. Greene, W. Kiessling, J. Ries, J. C. Zachos, D. L. Royer, S. Barker, T. M. Marchitto Jr., R. Moyer, C. Pelejero, P. Ziveri, G. L. Foster, B. Williams, The geological record of ocean acidification. Science 335, 1058–1063 (2012).

Kump, L.R., T.J. Bralower, and A. Ridgwell (2009)  Ocean acidification in deep time. Oceanography 22(4):94–107, http://dx.doi.org/10.5670/oceanog.2009.100

Seth D. Burgess, Samuel Bowring, and Shu-zhong Shen, High-precision timeline for Earth’s most severe extinction, PNAS 2014, doi:10.1073/pnas.1317692111