Late Ordovician mass extinction

The Late Ordovician mass extinction (LOME), sometimes known as the end-Ordovician mass extinction or the Ordovician-Silurian extinction, is the first of the "big five" major mass extinction events in Earth's history, occurring roughly 445 million years ago (Ma).^[1] It is often considered to be the second-largest known extinction event, in terms of the percentage of genera that became extinct.^[2][3] Extinction was global during this interval, eliminating 49–60% of marine genera and nearly 85% of marine species.^[4] Under most tabulations, only the Permian-Triassic mass extinction exceeds the Late Ordovician mass extinction in biodiversity loss. The extinction event abruptly affected all major taxonomic groups and caused the disappearance of one third of all brachiopod and bryozoan families, as well as numerous groups of conodonts, trilobites, echinoderms, corals, bivalves, and graptolites.^[5][6] Despite its taxonomic severity, the Late Ordovician mass extinction did not produce major changes to ecosystem structures compared to other mass extinctions, nor did it lead to any particular morphological innovations. Diversity gradually recovered to pre-extinction levels over the first 5 million years of the Silurian period.^{[7][8][9][10]}

Marine extinction intensity during Phanerozoic

%

Millions of years ago

(H)

K–Pg

Tr–J

P–Tr

Cap

Late D

O–S

The blue graph shows the apparent percentage (not the absolute number) of marine animal genera becoming extinct during any given time interval. It does not represent all marine species, just those that are readily fossilized. The labels of the traditional "Big Five" extinction events and the more recently recognised Capitanian mass extinction event are clickable links; see Extinction event for more details. (source and image info)

The Late Ordovician mass extinction is traditionally considered to occur in two distinct pulses.^[10] The first pulse (interval), known as LOMEI-1,^[11] began at the boundary between the Katian and Hirnantian stages of the Late Ordovician epoch. This extinction pulse is typically attributed to the Late Ordovician glaciation, which abruptly expanded over Gondwana at the beginning of the Hirnantian and shifted the Earth from a greenhouse to icehouse climate.^[6][12] Cooling and a falling sea level brought on by the glaciation led to habitat loss for many organisms along the continental shelves, especially endemic taxa with restricted temperature tolerance and latitudinal range.^[13][14][12] During this extinction pulse there were also several marked changes in biologically responsive carbon and oxygen isotopes.^[10] Marine life partially rediversified during the cold period and a new cold-water ecosystem, the "Hirnantia fauna", was established.^[15][10]

The second pulse (interval) of extinction, referred to as LOMEI-2,^[11] occurred in the later half of the Hirnantian as the glaciation abruptly receded and warm conditions returned. The second pulse was associated with intense worldwide anoxia (oxygen depletion) and euxinia (toxic sulfide production), which persisted into the subsequent Rhuddanian stage of the Silurian Period.^[16][10][17]

Some researchers have proposed the existence of a third distinct pulse of the mass extinction during the early Rhuddanian, evidenced by a negative carbon isotope excursion and a pulse of anoxia into shelf environments amidst already low background oxygen levels. Others, however, have argued that Rhuddanian anoxia was simply part of the second pulse, which according to this view was longer and more drawn out than most authors suggest.^[18]

Impact on life

Ecological impacts

The Late Ordovician mass extinction followed the Great Ordovician Biodiversification Event (GOBE), one of the largest surges of increasing biodiversity in the geological and biological history of the Earth.^[19] At the time of the extinction, most complex multicellular organisms lived in the sea, and the only evidence of life on land are rare spores from small early land plants.

At the time of the extinction, around 100 marine families became extinct, covering about 49%^[20] of genera (a more reliable estimate than species). The brachiopods and bryozoans were strongly impacted, along with many of the trilobite, conodont and graptolite families.^[10] The extinction was divided into two major extinction pulses. The first pulse occurred at the base of the global Metabolograptus extraordinarius graptolite biozone, which marks the end of the Katian stage and the start of the Hirnantian stage. The second pulse of extinction occurred in the later part of the Hirnantian stage, coinciding with the Metabolograptus persculptus zone. Each extinction pulse affected different groups of animals and was followed by a rediversification event. Statistical analysis of marine losses at this time suggests that the decrease in diversity was mainly caused by a sharp increase in extinctions, rather than a decrease in speciation.^[21]

Following such a major loss of diversity, Silurian communities were initially less complex and broader niched.^[1] Nonetheless, in South China, warm-water benthic communities with complex trophic webs thrived immediately following LOME.^[22] Highly endemic faunas, which characterized the Late Ordovician, were replaced by faunas that were amongst the most cosmopolitan in the Phanerozoic, biogeographic patterns that persisted throughout most of the Silurian.^[1] LOME had few of the long-term ecological impacts associated with the Permian–Triassic and Cretaceous–Paleogene extinction events.^[7][9] Furthermore, biotic recovery from LOME proceeded at a much faster rate than it did after the Permian-Triassic extinction.^[23] Nevertheless, a large number of taxa disappeared from the Earth over a short time interval, eliminating and altering the relative diversity and abundance of certain groups.^[1] The Cambrian-type evolutionary fauna nearly died out, and was unable to rediversify after the extinction.^[10]

Biodiversity changes in marine invertebrates

Brachiopods

Brachiopod diversity and composition was strongly affected, with the Cambrian-type inarticulate brachiopods (linguliforms and craniiforms) never recovering their pre-extinction diversity. Articulate (rhynchonelliform) brachiopods, part of the Paleozoic evolutionary fauna, were more variable in their response to the extinction. Some early rhynchonelliform groups, such as the Orthida and Strophomenida, declined significantly. Others, including the Pentamerida, Athyridida, Spiriferida, and Atrypida, were less affected and took the opportunity to diversify after the extinction.^[10][24]

The extinction pulse at the end of the Katian was selective in its effects, disproportionally affecting deep-water species and tropical endemics inhabiting epicontinental seas.^[10][14] The Foliomena fauna, an assemblage of thin-shelled species adapted for deep dysoxic (low oxygen) waters, went extinct completely in the first extinction pulse.^[10][14] The Foliomena fauna was formerly widespread and resistant to background extinction rates prior to the Hirnantian, so their unexpected extinction points towards the abrupt loss of their specific habitat.^[25] During the glaciation, a high-latitude brachiopod assemblage, the Hirnantia fauna, established itself along outer shelf environments in lower latitudes, probably in response to cooling.^[15] However, the Hirnantia fauna would meet its demise in the second extinction pulse, replaced by Silurian-style assemblages adapted for warmer waters.^[10][1][26]

The brachiopod survival intervals following the second pulse spanned the terminal Hirnantian to the middle Rhuddanian, after which the recovery interval began and lasted until the early Aeronian.^[27] Overall, the brachiopod recovery in the late Rhuddanian was rapid.^[28] Brachiopod survivors of the mass extinction tended to be endemic to one palaeoplate or even one locality in the survival interval in the earliest Silurian, though their ranges geographically expanded over the course of the biotic recovery.^[29] The region around what is today Oslo was a hotbed of atrypide rediversification.^[30] Brachiopod recovery consisted mainly of the reestablishment of cosmopolitan brachiopod taxa from the Late Ordovician.^[31] Progenitor taxa that arose following the mass extinction displayed numerous novel adaptations for resisting environmental stresses.^[32] Although some brachiopods did experience the Lilliput effect in response to the extinction, this phenomenon was not particularly widespread compared to other mass extinctions.^[33]

Trilobites

Trilobites were hit hard by both phases of the extinction, with about 70% of genera and 50% of families going extinct between the Katian and Silurian. The extinction disproportionately affected deep water species and groups with fully planktonic larvae or adults. The order Agnostida was completely wiped out, and the formerly diverse Asaphida survived with only a single genus, Raphiophorus.^[34][35][10] A cool-water trilobite assemblage, the Mucronaspis fauna, coincides with the Hirnantia brachiopod fauna in the timing of its expansion and demise.^[1][26] Trilobite faunas after the extinction were dominated by families that appeared in the Ordovician and survived LOME, such as Encrinuridae and Odontopleuridae.^[36]

Bryozoans

Over a third of bryozoan genera went extinct, but most families survived the extinction interval and the group as a whole recovered in the Silurian. The hardest-hit subgroups were the cryptostomes and trepostomes, which never recovered the full extent of their Ordovician diversity. Bryozoan extinctions started in coastal regions of Laurentia, before high extinction rates shifted to Baltica by the end of the Hirnantian.^[37][10][1] Bryozoan biodiversity loss appears to have been a prolonged process which partially preceded the Hirnantian extinction pulses. Extinction rates among Ordovician bryozoan genera were actually higher in the early and late Katian, and origination rates sharply dropped in the late Katian and Hirnantian.^[38]

Echinoderms

About 70% of crinoid genera died out. Early studies of crinoid biodiversity loss by Jack Sepkoski overestimated crinoid biodiversity losses during LOME.^[39] Most extinctions occurred in the first pulse. However, they rediversified quickly in tropical areas and reacquired their pre-extinction diversity not long into the Silurian. Many other echinoderms became very rare after the Ordovician, such as the cystoids, edrioasteroids, and other early crinoid-like groups.^[10][1]

Sponges

Stromatoporoid generic and familial taxonomic diversity was not significantly impacted by the mass extinction.^[40] Sponges thrived and dominated marine ecosystems in South China immediately after the extinction event,^[41] colonising depauperate, anoxic environments in the earliest Rhuddanian.^[42] Their pervasiveness in marine environments after the biotic crisis has been attributed to drastically decreased competition and an abundance of vacant niches left behind by organisms that perished in the catastrophe.^[43] Sponges may have assisted the recovery of other sessile suspension feeders: by helping stabilise sediment surfaces, they enabled bryozoans, brachiopods, and corals to recolonise the seafloor.^[44]

Glaciation and cooling

Main article: Late Ordovician glaciation

The first pulse of the Late Ordovician Extinction has typically been attributed to the Late Ordovician Glaciation, which is unusual among mass extinctions and has made LOME an outlier.^[45] Although there was a longer cooling trend in Middle and Lower Ordovician, the most severe and abrupt period of glaciation occurred in the Hirnantian stage, which was bracketed by both pulses of the extinction.^[46] The rapid continental glaciation was centered on Gondwana, which was located at the South Pole in the Late Ordovician. The Hirnantian glaciation is considered one of the most severe ice ages of the Paleozoic, which previously maintained the relatively warm climate conditions of a greenhouse earth.^[19]

 

An illustration depicting Cameroceras shells sticking out of the mud as a result of draining seaways during the Ordovician-Silurian Extinction event.

The cause of the glaciation is heavily debated. The late Ordovician glaciation was preceded by a fall in atmospheric carbon dioxide (from 7,000 ppm to 4,400 ppm).^[47][48] Atmospheric and oceanic CO₂ levels may have fluctuated with the growth and decay of Gondwanan glaciation. The appearance and development of terrestrial plants and microphytoplankton, which consumed atmospheric carbon dioxide, may have diminished the greenhouse effect and promoting the transition of the climatic system to the glacial mode.^[49][16] Heavy silicate weathering of the uplifting Appalachians and Caledonides occurred during the Late Ordovician, which sequestered CO₂.^[50] In the Hirnantian stage the volcanism diminished,^[51] and the continued weathering caused a significant and rapid draw down of CO₂ coincident with the rapid and short ice age.^[50][48] As Earth cooled and sea levels dropped, highly weatherable carbonate platforms became exposed above water, enkindling a positive feedback loop of inorganic carbon sequestration.^[52] A hypothetical large igneous province emplaced during the Katian whose existence is unproven has been speculated to have been the sink that absorbed carbon dioxide and precipitated Hirnantian cooling.^[53] Alternatively, volcanic activity may have caused the cooling by supplying sulphur aerosols to the atmosphere and generating severe volcanic winters that triggered a runaway ice-albedo positive feedback loop.^[54] In addition, volcanic fertilisation of the oceans with phosphorus may have increased populations of photosynthetic algae and enhanced biological sequestration of carbon dioxide from the atmosphere.^[55] Increased burial of organic carbon is another method of drawing down carbon dioxide from the air that may have played a role in the Late Ordovician.^[56] Other studies point to an asteroid strike and impact winter as the culprit for the glaciation.^[57] True polar wander and the associated rapid palaeogeographic changes have also been proposed as a cause.^[58]

Two environmental changes associated with the glaciation were responsible for much of the Late Ordovician extinction. First, the cooling global climate was probably especially detrimental because the biota were adapted to an intense greenhouse, especially because most shallow sea habitats in the Ordovician were located in the tropics.^[59] The southward shift of the polar front severely contracted the available latitudinal range of warm-adapted organisms.^[60] Second, sea level decline, caused by sequestering of water in the ice cap, drained the vast epicontinental seaways and eliminated the habitat of many endemic communities.^[13][61][62] The dispersed positions of the continents, in contrast to their position during the much less extinction-inducing Pleistocene glaciations, made glacioeustatic marine regression especially hazardous to marine life.^[63] Falling sea levels may have acted as a positive feedback loop accelerating further cooling; as shallow seas receded, carbonate-shelf production declined and atmospheric carbon dioxide levels correspondingly decreased, fostering even more cooling.^[56]

Ice caps formed on the southern supercontinent Gondwana as it drifted over the South Pole. Correlating rock strata have been detected in Late Ordovician rock strata of North Africa and then-adjacent northeastern South America, which were south-polar locations at the time. Glaciation locks up water from the world-ocean and interglacials free it, causing sea levels repeatedly to drop and rise; the vast, shallow Ordovician seas withdrew, which eliminated many ecological niches, then returned, carrying diminished founder populations lacking many whole families of organisms. Then they withdrew again with the next pulse of glaciation, eliminating biological diversity at each change. In the North African strata, five pulses of glaciation from seismic sections are recorded.^[64] In the Yangtze Platform, a relict warm-water fauna continued to persist because South China blocked the transport of cold waters from Gondwanan waters at higher latitudes.^[65]

This incurred a shift in the location of bottom water formation, shifting from low latitudes, characteristic of greenhouse conditions, to high latitudes, characteristic of icehouse conditions, which was accompanied by increased deep-ocean currents and oxygenation of the bottom water. An opportunistic fauna briefly thrived there, before anoxic conditions returned. The breakdown in the oceanic circulation patterns brought up nutrients from the abyssal waters. Surviving species were those that coped with the changed conditions and filled the ecological niches left by the extinctions.

However, not all studies agree that cooling and glaciation caused LOMEI-1. One study suggests that the first pulse began not during the rapid Hirnantian ice cap expansion but in an interval of deglaciation following it.^[66]

Anoxia and euxinia

Another heavily-discussed factor in the Late Ordovician mass extinction is anoxia, the absence of dissolved oxygen in seawater.^[11] Anoxia not only deprives most life forms of a vital component of respiration, it also encourages the formation of toxic metal ions and other compounds. One of the most common of these poisonous chemicals is hydrogen sulfide, a biological waste product and major component of the sulfur cycle. Oxygen depletion when combined with high levels of sulfide is called euxinia. Though less toxic, ferrous iron (Fe²⁺) is another substance which commonly forms in anoxic waters.^[67] Anoxia is the most common culprit for the second pulse of the Late Ordovician mass extinction and is connected to many other mass extinctions throughout geological time.^[17][50] It may have also had a role in the first pulse of the Late Ordovician mass extinction,^[67] though support for this hypothesis is inconclusive and contradicts other evidence for high oxygen levels in seawater during the glaciation.^[68][50]

Early Hirnantian anoxia

 

 

An excursion in the δ³⁴S ratio of pyrite (top) has been attributed to widespread deep-sea anoxia during the Hirnantian glaciation. However, sulfate-reducing bacteria (bottom) could instead have been responsible for the excursion without contributing to anoxia.

Some geologists have argued that anoxia played a role in the first extinction pulse, though this hypothesis is controversial. In the early Hirnantian, shallow-water sediments throughout the world experience a large positive excursion in the δ³⁴S ratio of buried pyrite. This ratio indicates that shallow-water pyrite which formed at the beginning of the glaciation had a decreased proportion of ³²S, a common lightweight isotope of sulfur. ³²S in the seawater could hypothetically be used up by extensive deep-sea pyrite deposition.^[69] The Ordovician ocean also had very low levels of sulfate, a nutrient which would otherwise resupply ³²S from the land. Pyrite forms most easily in anoxic and euxinic environments, while better oxygenation encourages the formation of gypsum instead.^[67] As a result, anoxia and euxinia would need to be common in the deep sea to produce enough pyrite to shift the δ³⁴S ratio.^[70][71]

Thallium isotope ratios can also be used as indicators of anoxia. A major positive ε²⁰⁵Tl excursion in the late Katian, just before the Katian-Hirnantian boundary, likely reflects a global enlargement of oxygen minimum zones. During the late Katian, thallium isotopic perturbations indicating proliferation of anoxic waters notably preceded the appearance of other geochemical indicators of the expansion of anoxia.^[72]

A more direct proxy for anoxic conditions is Fe_HR/Fe_T. This ratio describes the comparative abundance of highly reactive iron compounds which are only stable without oxygen. Most geological sections corresponding to the beginning of the Hirnantian glaciation have Fe_HR/Fe_T below 0.38, indicating oxygenated waters.^[70] However, higher Fe_HR/Fe_T values are known from a few deep-water early Hirnantian sequences found in China^[71] and Nevada.^[70] Elevated Fe_Py/Fe_HR values have also been found in association with LOMEI-1,^[71] including ones above 0.8 that are tell-tale indicators of euxinia.^[70]

Glaciation could conceivably trigger anoxic conditions, albeit indirectly. If continental shelves are exposed by falling sea levels, then organic surface runoff flows into deeper oceanic basins. The organic matter would have more time to leach out phosphate and other nutrients before being deposited on the seabed. Increased phosphate concentration in the seawater would lead to eutrophication and then anoxia. Deep-water anoxia and euxinia would impact deep-water benthic fauna, as expected for the first pulse of extinction. Chemical cycle disturbances would also steepen the chemocline, restricting the habitable zone of planktonic fauna which also go extinct in the first pulse. This scenario is congruent with both organic carbon isotope excursions and general extinction patterns observed in the first pulse.^[67]

However, data supporting deep-water anoxia during the glaciation contrasts with more extensive evidence for well-oxygenated waters. Black shales, which are indicative of an anoxic environment, become very rare in the early Hirnantian compared to surrounding time periods. Although early Hirnantian black shales can be found in a few isolated ocean basins (such as the Yangtze platform of China), from a worldwide perspective these correspond to local events.^[50] Some Chinese sections record an early Hirnantian increase in the abundance of Mo-98, a heavy isotope of molybdenum. This shift can correspond to a balance between minor local anoxia^[73] and well-oxygenated waters on a global scale.^[74] Other trace elements point towards increased deep-sea oxygenation at the start of the glaciation.^[75][76] Oceanic current modelling suggest that glaciation would have encouraged oxygenation in most areas, apart from the Paleo-Tethys ocean.^[77] Devastation of the Dicranograptidae-Diplograptidae-Orthograptidae (DDO) graptolite fauna, which was well adapted to anoxic conditions, further suggests that LOMEI-1 was associated with increased oxygenation of the water column and not the other way around.^[78]

Deep-sea anoxia is not the only explanation for the δ³⁴S excursion of pyrite. Carbonate-associated sulfate maintains high ³²S levels, indicating that seawater in general did not experience ³²S depletion during the glaciation. Even if pyrite burial did increase at that time, its chemical effects would have been far too slow to explain the rapid excursion or extinction pulse. Instead, cooling may lower the metabolism of warm-water aerobic bacteria, reducing decomposition of organic matter. Fresh organic matter would eventually sink down and supply nutrients to sulfate-reducing microbes living in the seabed. Sulfate-reducing microbes prioritize ³²S during anaerobic respiration, leaving behind heavier isotopes. A bloom of sulfate-reducing microbes can quickly account for the δ³⁴S excursion in marine sediments without a corresponding decrease in oxygen.^[68]

A few studies have proposed that the first extinction pulse did not begin with the Hirnantian glaciation, but instead corresponds to an interglacial period or other warming event. Anoxia would be the most likely mechanism of extinction in a warming event, as evidenced by other extinctions involving warming.^[79][80][81] However, this view of the first extinction pulse is controversial and not widely accepted.^[50][82]

Late Hirnantian anoxia

The late Hirnantian experienced a dramatic increase in the abundance of black shales. Coinciding with the retreat of the Hirnantian glaciation, black shale expands out of isolated basins to become the dominant oceanic sediment at all latitudes and depths. The worldwide distribution of black shales in the late Hirnantian is indicative of a global anoxic event,^[50] which has been termed the Hirnantian ocean anoxic event (HOAE).^[83][17] Corresponding to widespread anoxia are δ³⁴S_CAS,^[84][85] δ⁹⁸Mo,^[74][73] δ²³⁸U,^[83][86][17] and εNd(t) excursions found in many different regions.^[87] At least in European sections, late Hirnantian anoxic waters were originally ferruginous (dominated by ferrous iron) before gradually becoming more euxinic.^[67] In the Yangtze Sea, located on the western margins of the South China microcontinent, the second extinction pulse occurred alongside intense euxinia which spread out from the middle of the continental shelf.^[88][71] Mercury loading in South China during LOMEI-2 was likely related to euxinia.^[89] However, some evidence suggests that the top of the water column in the Ordovician oceans remained well oxygenated even as the seafloor became deoxygenated.^[90] On a global scale, euxinia was probably one or two orders of magnitude more prevalent than in the modern day. Global anoxia may have lasted more than 3 million years, persisting through the entire Rhuddanian stage of the Silurian period. This would make the Hirnantian-Rhuddanian anoxia one of the longest-lasting anoxic events in geologic time.^[17]

 

Cyanobacteria blooms after the Hirnantian glaciation likely caused the Hirnantian-Rhuddanian global anoxic event, the main factor behind the second extinction pulse.

The cause of the Hirnantian-Rhuddanian anoxic event is uncertain. Like most global anoxic events, an increased supply of nutrients (such as nitrates and phosphates) would encourage algal or microbial blooms that deplete oxygen levels in the seawater. The most likely culprits are cyanobacteria, which can use nitrogen fixation to produce usable nitrogen compounds in the absence of nitrates. Nitrogen isotopes during the anoxic event record high rates of denitrification, a biological process which depletes nitrates. The Nitrogen-fixing ability of cyanobacteria would give them an edge over inflexible competitors like eukaryotic algae.^{[50][91][92][93]} At Anticosti Island, a uranium isotope excursion consistent with anoxia actually occurs prior to indicators of receding glaciation. This may suggest that the Hirnantian-Rhuddanian anoxic event (and its corresponding extinction) began during the glaciation, not after it. Cool temperatures can lead to upwelling, cycling nutrients into productive surface waters via air and ocean cycles.^[83] Upwelling could instead be encouraged by increasing oceanic stratification through an input of freshwater from melting glaciers. This would be more reasonable if the anoxic event coincided with the end of glaciation, as supported by most other studies.^[50] However, oceanic models argue that marine currents would recover too quickly for freshwater disruptions to have a meaningful effect on nutrient cycles. Retreating glaciers could expose more land to weathering, which would be a more sustained source of phosphates flowing into the ocean.^[77] There is also evidence implicating volcanism as a contributor to Late Hirnantian anoxia.^[94]

There were few clear patterns of extinction associated with the second extinction pulse. Every region and marine environment experienced the second extinction pulse to some extent. Many taxa which survived or diversified after the first pulse were finished off in the second pulse. These include the Hirnantia brachiopod fauna and Mucronaspis trilobite fauna, which previously thrived in the cold glacial period. Other taxa such as graptolites and warm-water reef denizens were less affected.^[10][1][17] Sediments from China and Baltica seemingly show a more gradual replacement of the Hirnantia fauna after glaciation.^[95] Although this suggests that the second extinction pulse may have been a minor event at best, other paleontologists maintain that an abrupt ecological turnover accompanied the end of glaciation.^[26] There may be a correlation between the relatively slow recovery after the second extinction pulse, and the prolonged nature of the anoxic event which accompanied it.^[83][17] On the other hand, the occurrence of euxinic pulses similar in magnitude to LOMEI-2 during the Katian without ensuing biological collapses has caused some researchers to question whether euxinia alone could have been LOMEI-2's driver.^[96]

Early Rhuddanian anoxia

Deposition of black graptolite shales continued to be common into the earliest Rhuddanian, indicating that anoxia persisted well into the Llandovery. A sharp reduction in the average size of many organisms, likely attributable to the Lilliput effect, and the disappearance of many relict taxa from the Ordovician indicate a third extinction interval linked to an expansion of anoxic conditions into shallower shelf environments, particularly in Baltica. This sharp decline in dissolved oxygen concentrations was likely linked to a period of global warming documented by a negative carbon isotope excursion preserved in Baltican sediments.^[18]

Other potential factors

Metal poisoning

Toxic metals on the ocean floor may have dissolved into the water when the oceans' oxygen was depleted. An increase in available nutrients in the oceans may have been a factor, and decreased ocean circulation caused by global cooling may also have been a factor.^[83] Hg/TOC values from the Peri-Baltic region indicate noticeable spikes in mercury concentrations during the lower late Katian, the Katian-Hirnantian boundary, and the late Hirnantian.^[97]

The toxic metals may have killed life forms in lower trophic levels of the food chain, causing a decline in population, and subsequently resulting in starvation for the dependent higher feeding life forms in the chain.^[98][99]

Gamma-ray burst

A minority hypothesis to explain the first burst has been proposed by Philip Ball,^[100] Adrian Lewis Melott, and Brian C. Thomas,^[101][102] suggesting that the initial extinctions could have been caused by a gamma-ray burst originating from a hypernova in a nearby arm of the Milky Way galaxy, within 6,000 light-years of Earth. A ten-second burst would have stripped the Earth's atmosphere of half of its ozone almost immediately, exposing surface-dwelling organisms, including those responsible for planetary photosynthesis, to high levels of extreme ultraviolet radiation.^{[102][103][104]} Under this hypothesis, several groups of marine organisms with a planktonic lifestyle were more exposed to UV radiation than groups that lived on the seabed. It is estimated that 20% to 60% of the total phytoplankton biomass on Earth would have been killed in such an event because the oceans were mostly oligotrophic and clear during the Late Ordovician.^[105] This is consistent with observations that planktonic organisms suffered severely during the first extinction pulse. In addition, species dwelling in shallow water were more likely to become extinct than species dwelling in deep water, also consistent with the hypothetical effects of a galactic gamma-ray burst.

A gamma-ray burst could also explain the rapid expansion of glaciers, since the high energy rays would cause ozone, a greenhouse gas, to dissociate and its dissociated oxygen atoms to then react with nitrogen to form nitrogen dioxide, a darkly-coloured aerosol which cools the planet.^[106][102] It would also cohere with the major δ13C isotopic excursion indicating increased sequestration of carbon-12 out of the atmosphere, which would have occurred as a result of nitrogen dioxide, formed after the reaction of nitrogen and oxygen atoms dissociated by the gamma-ray burst, reacting with hydroxyl and raining back down to Earth as nitric acid, precipitating large quantities of nitrates that would have enhanced wetland productivity and sequestration of carbon dioxide.^[107][101] Although the gamma-ray burst hypothesis is consistent with some patterns at the onset of extinction, there is no unambiguous evidence that such a nearby gamma-ray burst ever happened.^[16]

Volcanism

Though more commonly associated with greenhouse gases and global warming, volcanoes may have cooled the planet and precipitated glaciation by discharging sulphur into the atmosphere.^[54] This is supported by a positive uptick in pyritic Δ³³S values, a geochemical signal of volcanic sulphur discharge, coeval with LOMEI-1.^[108]

More recently, in May 2020, a study suggested the first pulse of mass extinction was caused by volcanism which induced global warming and anoxia, rather than cooling and glaciation.^[109][81] Higher resolution of species diversity patterns in the Late Ordovician suggest that extinction rates rose significantly in the early or middle Katian stage, several million years earlier than the Hirnantian glaciation. This early phase of extinction is associated with large igneous province (LIP) activity, possibly that of the Alborz LIP of northern Iran,^[110] as well as a warming phase known as the Boda event.^{[111][112][113]} However, other research still suggests the Boda event was a cooling event instead.^[114]

Increased volcanic activity during the early late Katian and around the Katian-Hirnantian boundary is also implied by heightened mercury concentrations relative to total organic carbon.^[97][89] Marine bentonite layers associated with the subduction of the Junggar Ocean underneath the Yili Block have been dated to the late Katian, close to the Katian-Hirnantian boundary.^[115]

Volcanic activity could also provide a plausible explanation for anoxia during the first pulse of the mass extinction. A volcanic input of phosphorus, which was insufficient to enkindle persistent anoxia on its own, may have triggered a positive feedback loop of phosphorus recycling from marine sediments, sustaining widespread marine oxygen depletion over the course of LOMEI-1.^[11] Also, the weathering of nutrient-rich volcanic rocks emplaced during the middle and late Katian likely enhanced the reduction in dissolved oxygen.^[89] Intense volcanism also fits in well with the attribution of euxinia as the main driver of LOMEI-2; sudden volcanism at the Ordovician-Silurian boundary is suggested to have supplied abundant sulphur dioxide, greatly facilitating the development of euxinia.^[116]

Other papers have criticised the volcanism hypothesis, claiming that volcanic activity was relatively low in the Ordovician and that superplume and LIP volcanic activity is especially unlikely to have caused the mass extinction at the end of the Ordovician.^[2] A 2022 study argued against a volcanic cause of LOME, citing the lack of mercury anomalies and the discordance between deposition of bentonites and redox changes in drillcores from South China straddling the Ordovician-Silurian boundary.^[117] Mercury anomalies at the end of the Ordovician relative to total organic carbon, or Hg/TOC, that some researchers have attributed to large-scale volcanism have been reinterpreted by some to be flawed because the main mercury host in the Ordovician was sulphide, and thus Hg/TS should be used instead;^[118] Hg/TS values show no evidence of volcanogenic mercury loading,^[119] a finding bolstered by ∆¹⁹⁹Hg measurements much higher than would be expected for volcanogenic mercury input.^[118]

Asteroid impact

A 2023 paper points to the Deniliquin multiple-ring feature in southeastern Australia, which has been dated to around the start of LOMEI-1, for initiating the intense Hirnantian glaciation and the first pulse of the extinction event. According to the paper, it still requires further research to test the idea.^[57][120]

See also

• Global catastrophic risk
• Near-Earth supernova
• Anoxic event
• Late Devonian extinction
• Capitanian mass extinction event
• Permian–Triassic extinction event
• Triassic–Jurassic extinction event
• Cretaceous–Paleogene extinction event
• Andean-Saharan glaciation

Sources

1. Harper, D. A. T.; Hammarlund, E. U.; Rasmussen, C. M. Ø. (May 2004). "End Ordovician extinctions: A coincidence of causes". Gondwana Research. 25 (4): 1294–1307. Bibcode:2014GondR..25.1294H. doi:10.1016/j.gr.2012.12.021.
2. Isozaki, Yukio; Servais, Thomas (8 December 2017). "The Hirnantian (Late Ordovician) and end-Guadalupian (Middle Permian) mass-extinction events compared". Lethaia. 51 (2): 173–186. doi:10.1111/let.12252. Retrieved 23 October 2022.
3. Marshall, Michael (24 May 2010). "The history of ice on Earth". New Scientist. Retrieved 12 April 2018.
4. Christie, M.; Holland, S. M.; Bush, A. M. (2013). "Contrasting the ecological and taxonomic consequences of extinction". Paleobiology. 39 (4): 538–559. Bibcode:2013Pbio...39..538C. doi:10.1666/12033. S2CID 85313761. ProQuest 1440071324.
5. Elewa, Ashraf (2008). Late Ordovician Mass Extinction. Springer. p. 252. ISBN 978-3-540-75915-7.
6. Sole, R. V.; Newman, M. (2002). "The earth system: biological and ecological dimensions of global environment change". Encyclopedia of Global Environmental Change, Volume Two: Extinctions and Biodiversity in the Fossil Record. John Wiley & Sons. pp. 297–391.
7. Droser, Mary L.; Bottjer, David J.; Sheehan, Peter M. (1997-02-01). "Evaluating the ecological architecture of major events in the Phanerozoic history of marine invertebrate life". Geology. 25 (2): 167–170. Bibcode:1997Geo....25..167D. doi:10.1130/0091-7613(1997)025<0167:ETEAOM>2.3.CO;2. ISSN 0091-7613.
8. Droser, Mary L.; Bottjer, David J.; Sheehan, Peter M.; McGhee, George R. (2000-08-01). "Decoupling of taxonomic and ecologic severity of Phanerozoic marine mass extinctions". Geology. 28 (8): 675–678. Bibcode:2000Geo....28..675D. doi:10.1130/0091-7613(2000)28<675:DOTAES>2.0.CO;2. ISSN 0091-7613.
9. Brenchley, P. J.; Marshall, J. D.; Underwood, C. J. (2001). "Do all mass extinctions represent an ecological crisis? Evidence from the Late Ordovician". Geological Journal. 36 (3–4): 329–340. doi:10.1002/gj.880. ISSN 1099-1034. S2CID 128870184.
10. Sheehan, Peter M (May 2001). "The Late Ordovician Mass Extinction". Annual Review of Earth and Planetary Sciences. 29 (1): 331–364. Bibcode:2001AREPS..29..331S. doi:10.1146/annurev.earth.29.1.331. ISSN 0084-6597.
11. Qiu, Zhen; Zou, Caineng; Mills, Benjamin J. W.; Xiong, Yijun; Tao, Huifei; Lu, Bin; Liu, Hanlin; Xiao, Wenjiao; Poulton, Simon W. (5 April 2022). "A nutrient control on expanded anoxia and global cooling during the Late Ordovician mass extinction". Communications Earth & Environment. 3 (1): 82. Bibcode:2022ComEE...3...82Q. doi:10.1038/s43247-022-00412-x.
12. . Archived from the original on 2008-05-09.
13. Finnegan, Seth; Heim, Noel A.; Peters, Shanan E.; Fischer, Woodward W. (17 April 2012). "Climate change and the selective signature of the Late Ordovician mass extinction". Proceedings of the National Academy of Sciences of the United States of America. 109 (18): 6829–6834. Bibcode:2012PNAS..109.6829F. doi:10.1073/pnas.1117039109. PMC 3345012. PMID 22511717.
14. Finnegan, Seth; Rasmussen, Christian M. Ø.; Harper, David A. T. (2016-04-27). "Biogeographic and bathymetric determinants of brachiopod extinction and survival during the Late Ordovician mass extinction". Proceedings of the Royal Society B: Biological Sciences. 283 (1829): 20160007. doi:10.1098/rspb.2016.0007. PMC 4855380. PMID 27122567.
15. Jia-Yu, Rong; Xu, Chen; Harper, David A. T. (2 January 2007). "The latest Ordovician Hirnantia Fauna (Brachiopoda) in time and space". Lethaia. 35 (3): 231–249. doi:10.1111/j.1502-3931.2002.tb00081.x. Retrieved 26 December 2022.
16. Barash, M. (November 2014). "Mass Extinction of the Marine Biota at the Ordovician–Silurian Transition Due to Environmental Changes". Oceanology. 54 (6): 780–787. Bibcode:2014Ocgy...54..780B. doi:10.1134/S0001437014050014. S2CID 129788917.
17. Stockey, Richard G.; Cole, Devon B.; Planavsky, Noah J.; Loydell, David K.; Frýda, Jiří; Sperling, Erik A. (14 April 2020). "Persistent global marine euxinia in the early Silurian". Nature Communications. 11 (1): 1804. Bibcode:2020NatCo..11.1804S. doi:10.1038/s41467-020-15400-y. ISSN 2041-1723. PMC 7156380. PMID 32286253. S2CID 215750045.
18. Baarli, B. Gudveig (1 February 2014). "The early Rhuddanian survival interval in the Lower Silurian of the Oslo Region: A third pulse of the end-Ordovician extinction". Palaeogeography, Palaeoclimatology, Palaeoecology. 395: 29–41. doi:10.1016/j.palaeo.2013.12.018. Retrieved 15 November 2022.
19. Munnecke, A.; Calner, M.; Harper, D. A. T.; Servais, T. (2010). "Ordovician and Silurian sea-water chemistry, sea level, and climate: A synopsis". Palaeogeography, Palaeoclimatology, Palaeoecology. 296 (3–4): 389–413. Bibcode:2010PPP...296..389M. doi:10.1016/j.palaeo.2010.08.001.
20. Rohde & Muller; Muller, RA (2005). "Cycles in Fossil Diversity". Nature. 434 (7030): 208–210. Bibcode:2005Natur.434..208R. doi:10.1038/nature03339. PMID 15758998. S2CID 32520208.
21. Bambach, R. K.; Knoll, A.H.; Wang, S.C. (December 2004). "Origination, extinction, and mass depletions of marine diversity". Paleobiology. 30 (4): 522–542. doi:10.1666/0094-8373(2004)030<0522:OEAMDO>2.0.CO;2. S2CID 17279135.
22. Jeon, Juwan; Li, Yeon; Kershaw, Stephen; Chen, Zhongyang; Ma, Junye; Lee, Jeong-Hyun; Liang, Kun; Yu, Shenyang; Huang, Bing; Zhang, Yuandong (1 October 2022). "Nearshore warm-water biota development in the aftermath of the Late Ordovician Mass Extinction in South China". Palaeogeography, Palaeoclimatology, Palaeoecology. 603: 111182. Bibcode:2022PPP...60311182J. doi:10.1016/j.palaeo.2022.111182. S2CID 251480863. Retrieved 16 April 2023.
23. Cocks, L. Robin M.; Jia-yu, Rong (1 September 2007). "Earliest Silurian faunal survival and recovery after the end Ordovician glaciation: evidence from the brachiopods". Transactions of the Royal Society of Edinburgh. 98 (3–4): 291–301. doi:10.1017/S175569100807566X. S2CID 140634879. Retrieved 25 May 2023.
24. Harper, David A. T.; Jia-Yu, Rong (2001). "Palaeozoic brachiopod extinctions, survival and recovery: patterns within the rhynchonelliformeans". Geological Journal. 36 (3–4): 317–328. doi:10.1002/gj.897. ISSN 1099-1034. S2CID 129370611.
25. Finnegan, Seth; Rasmussen, Christian M. Ø.; Harper, David A. T. (2017-09-30). "Identifying the most surprising victims of mass extinction events: an example using Late Ordovician brachiopods". Biology Letters. 13 (9): 20170400. doi:10.1098/rsbl.2017.0400. PMC 5627174. PMID 28954854.
26. Rong, Jiayu; Harper, David A. T.; Huang, Bing; Li, Rongyu; Zhang, Xiaole; Chen, Di (2020-09-01). "The latest Ordovician Hirnantian brachiopod faunas: New global insights". Earth-Science Reviews. 208: 103280. Bibcode:2020ESRv..20803280R. doi:10.1016/j.earscirev.2020.103280. ISSN 0012-8252. S2CID 225549860.
27. Jia-Yu, Rong; Harper, David A. T. (31 January 2000). "Brachiopod survival and recovery from the latest Ordovician mass extinctions in South China". Geological Journal. 34 (4): 321–348. doi:10.1002/(SICI)1099-1034(199911/12)34:4<321::AID-GJ809>3.0.CO;2-I. Retrieved 16 April 2023.
28. Rong, Jia-yu; Shen, Shu-zhong (1 December 2002). "Comparative analysis of the end-Permian and end-Ordovician brachiopod mass extinctions and survivals in South China". Palaeogeography, Palaeoclimatology, Palaeoecology. 188 (1–2): 25–38. Bibcode:2002PPP...188...25R. doi:10.1016/S0031-0182(02)00507-2. Retrieved 10 August 2023.
29. Huang, Bing; Rong, Jiayu; Cocks, L. Robin M. (1 February 2012). "Global palaeobiogeographical patterns in brachiopods from survival to recovery after the end-Ordovician mass extinction". Palaeogeography, Palaeoclimatology, Palaeoecology. 317–318: 196–205. Bibcode:2012PPP...317..196H. doi:10.1016/j.palaeo.2012.01.009. Retrieved 16 April 2023.
30. Baarli, B. Gudveig (1 January 2022). "The smooth, spire-bearing brachiopods after the terminal Ordovician extinction through lower Llandovery in the central Oslo region, Norway". Journal of Paleontology. 96 (1): 81–111. doi:10.1017/jpa.2021.72. S2CID 238707360. Retrieved 25 May 2023.
31. Huang, Bing; Jin, Jisuo; Rong, Jia-Yu (15 March 2018). "Post-extinction diversification patterns of brachiopods in the early–middle Llandovery, Silurian". Palaeogeography, Palaeoclimatology, Palaeoecology. 493: 11–19. Bibcode:2018PPP...493...11H. doi:10.1016/j.palaeo.2017.12.025. Retrieved 23 November 2022.
32. Rong, Jiayu; Zhan, Renbin (October 1999). "Chief sources of brachiopod recovery from the end Ordovician mass extinction with special references to progenitors". Science in China Series D: Earth Sciences. 42 (5): 553–560. Bibcode:1999ScChD..42..553R. doi:10.1007/BF02875250. S2CID 129323463. Retrieved 16 April 2023.
33. Huang, Bing; Harper, David A. T.; Zhan, Renbin; Rong, Jiayu (15 January 2010). "Can the Lilliput Effect be detected in the brachiopod faunas of South China following the terminal Ordovician mass extinction?". Palaeogeography, Palaeoclimatology, Palaeoecology. 285 (3–4): 277–286. Bibcode:2010PPP...285..277H. doi:10.1016/j.palaeo.2009.11.020. Retrieved 15 January 2023.
34. Chatterton, Brian D. E.; Speyer, Stephen E. (1989). "Larval ecology, life history strategies, and patterns of extinction and survivorship among Ordovician trilobites". Paleobiology. 15 (2): 118–132. Bibcode:1989Pbio...15..118C. doi:10.1017/S0094837300009313. ISSN 0094-8373. JSTOR 2400847. S2CID 89379920.
35. Owen, Alan W.; Harper, David A.T.; Rong, Jia-Yu (1991). "Hirnantian trilobites and brachiopods in space and time" (PDF). In C.R. Barnes, S.H. Williams (ed.). Advances in Ordovician Geology. Geological Survey of Canada. pp. 179–190. doi:10.4095/132187.
36. Bault, Valentin; Balseiro, Diego; Monnet, Claude; Crônier, Catherine (July 2022). "Post-Ordovician trilobite diversity and evolutionary faunas". Earth-Science Reviews. 230. doi:10.1016/j.earscirev.2022.104035.
37. Tuckey, Michael E.; Anstey, Robert L. (1992). "Late Ordovician extinctions of bryozoans". Lethaia. 25 (1): 111–117. doi:10.1111/j.1502-3931.1992.tb01795.x. ISSN 1502-3931.
38. Ernst, Andrej (2018). "Diversity dynamics of Ordovician Bryozoa". Lethaia. 51 (2): 198–206. doi:10.1111/let.12235. ISSN 1502-3931.
39. Ausich, William I.; Peters, Shanan E. (8 April 2016). "A revised macroevolutionary history for Ordovician — Early Silurian crinoids". Paleobiology. 31 (3): 538–551. doi:10.1666/0094-8373(2005)031[0538:ARMHFO]2.0.CO;2. S2CID 85903232. Retrieved 25 May 2023.
40. Nestor, Heldur; Copper, Paul; Stock, Carl (1 January 2010). Late Ordovician and Early Silurian stromatoporoid sponges from Anticosti Island, eastern Canada: Crossing the O/S mass extinction. Canadian Science Publishing. doi:10.1139/9780660199306. ISBN 9780660199306.
41. Botting, Joseph P.; Muir, Lacy A.; Wang, Wenhui; Qie, Wenkun; Tan, Jingqiang; Zhang, Linna; Zhang, Yuandong (September 2018). "Sponge-dominated offshore benthic ecosystems across South China in the aftermath of the end-Ordovician mass extinction". Gondwana Research. 61: 150–171. Bibcode:2018GondR..61..150B. doi:10.1016/j.gr.2018.04.014. S2CID 134827223. Retrieved 14 March 2023.
42. Wang, Yong; Botting, Joseph P.; Tan, Jing-Qiang; Li, Ming; Wang, Wen-Hui (April 2023). "Coupling of the recovery of earliest Silurian sponges and ocean redox conditions: Evidence from South China". Journal of Palaeogeography. 12 (2): 311–330. doi:10.1016/j.jop.2023.03.005.
43. Li, Lixia; Feng, Hongzhen; Janussen, Dorte; Reitner, Joachim (5 November 2015). "Unusual Deep Water sponge assemblage in South China—Witness of the end-Ordovician mass extinction". Scientific Reports. 5 (1): 16060. Bibcode:2015NatSR...516060L. doi:10.1038/srep16060. PMC 4633598. PMID 26538179. Retrieved 14 March 2023.
44. Botting, Joseph P.; Muir, Lacy A.; Zhang, Yuangdong; Ma, Xuan; Ma, Junye; Wang, Longwu; Zhang, Jianfang; Song, Yanyan; Fang, Xiang (9 February 2017). "Flourishing Sponge-Based Ecosystems after the End-Ordovician Mass Extinction". Current Biology. 27 (4): 556–562. doi:10.1016/j.cub.2016.12.061. PMID 28190724. S2CID 54525645.
45. Rasmussen, Christian M.Ø.; Vandenbroucke, Thijs R.A.; Nogues-Bravo, David; Finnegan, Seth (12 May 2023). "Was the Late Ordovician mass extinction truly exceptional?". Trends in Ecology & Evolution. 38 (9): 812–821. doi:10.1016/j.tree.2023.04.009. ISSN 0169-5347. PMID 37183151. S2CID 258672970. Retrieved 11 December 2023.
46. Trotter, Julie A.; Williams, Ian S.; Barnes, Christopher R.; Lécuyer, Christophe; Nicoll, Robert S. (25 July 2008). "Did Cooling Oceans Trigger Ordovician Biodiversification? Evidence from Conodont Thermometry". Science. 321 (5888): 550–554. Bibcode:2008Sci...321..550T. doi:10.1126/science.1155814. PMID 18653889. S2CID 28224399. Retrieved 26 December 2022.
47. Seth A. Young, Matthew R. Saltzman, William I. Ausich, André Desrochers, and Dimitri Kaljo, "Did changes in atmospheric CO₂ coincide with latest Ordovician glacial–interglacial cycles?", Palaeogeography, Palaeoclimatology, Palaeoecology, Vol. 296, No. 3–4, 15 October 2010, Pages 376–388.
48. Jeff Hecht, High-carbon ice age mystery solved, New Scientist, 8 March 2010 (retrieved 30 June 2014)
49. Lenton, Timothy M.; Crouch, Michael; Johnson, Martin; Pires, Nuno; Dolan, Liam (1 February 2012). "First plants cooled the Ordovician". Nature Geoscience. 5 (2): 86–89. Bibcode:2012NatGe...5...86L. doi:10.1038/ngeo1390. ISSN 1752-0908. Retrieved 18 October 2022.
50. Melchin, Michael J.; Mitchell, Charles E.; Holmden, Chris; Štorch, Peter (2013). "Environmental changes in the Late Ordovician–early Silurian: Review and new insights from black shales and nitrogen isotopes". Geological Society of America Bulletin. 125 (11–12): 1635–1670. Bibcode:2013GSAB..125.1635M. doi:10.1130/B30812.1. Retrieved 12 August 2023.
51. Wang, Yong; Jingqiang, Tan; Wang, Wenhui; Zhou, Lian; Tang, Peng; Kang, Xun; Xie, Wenquan; Wang, Zhanghu; Dick, Jeffrey (6 July 2022). "The influence of Late Ordovician volcanism on the marine environment based on high-resolution mercury data from South China". Geological Society of America Bulletin. 135 (3–4): 787–798. doi:10.1130/B36257.1. Retrieved 19 October 2022.
52. Kump, L. R.; Arthur, M. A.; Patzkowsky, M. E.; Gibbs, M. T.; Pinkus, D. S.; Sheehan, P. M. (15 August 1999). "A weathering hypothesis for glaciation at high atmospheric pCO2 during the Late Ordovician". Palaeogeography, Palaeoclimatology, Palaeoecology. 152 (1–2): 173–187. doi:10.1016/S0031-0182(99)00046-2. Retrieved 12 August 2023.
53. Lefebvre, Vincent; Servais, Thomas; François, Louis; Averbuch, Olivier (15 October 2010). "Did a Katian large igneous province trigger the Late Ordovician glaciation?: A hypothesis tested with a carbon cycle model". Palaeogeography, Palaeoclimatology, Palaeoecology. 296 (3–4): 310–319. doi:10.1016/j.palaeo.2010.04.010. Retrieved 25 May 2023.
54. Jones, David S.; Martini, Anna M.; Fike, David A.; Kaiho, Kunio (2017-07-01). "A volcanic trigger for the Late Ordovician mass extinction? Mercury data from south China and Laurentia". Geology. 45 (7): 631–634. Bibcode:2017Geo....45..631J. doi:10.1130/G38940.1. ISSN 0091-7613.
55. Longman, Jack; Mills, Benjamin J. W.; Manners, Hayley R.; Gernon, Thomas M.; Palmer, Martin R. (2 December 2021). "Late Ordovician climate change and extinctions driven by elevated volcanic nutrient supply". Nature Geoscience. 14 (12): 924–929. Bibcode:2021NatGe..14..924L. doi:10.1038/s41561-021-00855-5. hdl:10026.1/18128. S2CID 244803446. Retrieved 21 October 2022.
56. Saltzman, Matthew R.; Young, Seth A. (2005-02-01). "Long-lived glaciation in the Late Ordovician? Isotopic and sequence-stratigraphic evidence from western Laurentia". Geology. 33 (2): 109–112. Bibcode:2005Geo....33..109S. doi:10.1130/G21219.1. ISSN 0091-7613.
57. Glikson, Andrew Yoram (June 2023). "An asteroid impact origin of the Hirnantian (end-Ordovician) glaciation and mass extinction". Gondwana Research. 118: 153–159. doi:10.1016/j.gr.2023.02.019. S2CID 257273196. Retrieved 25 May 2023.
58. Jing, Xianqing; Yang, Zhenyu; Mitchell, Ross N.; Tong, Yabo; Zhu, Min; Wan, Bo (26 December 2022). "Ordovician–Silurian true polar wander as a mechanism for severe glaciation and mass extinction". Nature Communications. 13 (1): 7941. Bibcode:2022NatCo..13.7941J. doi:10.1038/s41467-022-35609-3. PMC 9792554. PMID 36572674.
59. Saupe, Erin E.; Qiao, Huijie; Donnadieu, Yannick; Farnsworth, Alexander; Kennedy-Asser, Alan T.; Ladant, Jean-Baptiste; Lunt, Daniel J.; Pohl, Alexandre; Valdes, Paul; Finnegan, Seth (16 December 2019). "Extinction intensity during Ordovician and Cenozoic glaciations explained by cooling and palaeogeography". Nature Geoscience. 13 (1): 65–70. doi:10.1038/s41561-019-0504-6. hdl:1983/c88c3d46-e95d-43e6-aeaf-685580089635. S2CID 209381464. Retrieved 22 October 2022.
60. Vandenbroucke, Thijs R. A.; Armstrong, Howard A.; Williams, Mark; Paris, Florentin; Zalasiewicz, Jan A.; Sappe, Koen; Nõlvak, Jaak; Challands, Thomas J.; Verniers, Jacques; Servais, Thomas (24 August 2010). "Polar front shift and atmospheric CO2 during the glacial maximum of the Early Paleozoic Icehouse". Proceedings of the National Academy of Sciences of the United States of America. 107 (34): 14983–14986. doi:10.1073/pnas.1003220107. PMC 2930542. PMID 20696937.
61. Finney, Stanley C.; Berry, William B. N.; Cooper, John D.; Ripperdan, Robert L.; Sweet, Walter C.; Jacobson, Stephen R.; Soufiane, Azzedine; Achab, Aicha; Noble, Paula J. (1 March 1999). "Late Ordovician mass extinction: A new perspective from stratigraphic sections in central Nevada". Geology. 27 (3): 215–218. doi:10.1130/0091-7613(1999)027<0215:LOMEAN>2.3.CO;2. ISSN 0091-7613. Retrieved 10 September 2023.
62. Sheehan, Peter M. (April 1973). "The relation of Late Ordovician glaciation to the Ordovician-Silurian changeover in North American brachiopod faunas". Lethaia. 6 (2): 147–154. doi:10.1111/j.1502-3931.1973.tb01188.x. ISSN 0024-1164. Retrieved 11 December 2023 – via Wiley Online Library.
63. Grant, Peter R.; Grant, B. Rosemary; Huey, Raymond B.; Johnson, Marc T. J.; Knoll, Andrew H.; Schmitt, Johanna (19 June 2017). "Evolution caused by extreme events". Philosophical Transactions of the Royal Society B: Biological Sciences. 372 (1723): 20160146. doi:10.1098/rstb.2016.0146. ISSN 0962-8436. PMC 5434096. PMID 28483875.
64. (PDF). Archived from the original (PDF) on 2011-07-27. Retrieved 2009-07-22.{{cite web}}: CS1 maint: archived copy as title (link) IGCP meeting September 2004 reports pp 26f
65. Li, Yue; Matsumoto, Ryo; Kershaw, Steve (21 December 2005). "Sedimentary and biotic evidence of a warm-water enclave in the cooler oceans of the latest Ordovician glacial phase, Yangtze Platform, South China block". The Island Arc. 14 (4): 623–635. doi:10.1111/j.1440-1738.2005.00472.x. ISSN 1038-4871. S2CID 129101399.
66. Ghienne, Jean-François; Desrochers, André; Vanderbroucke, Thijs R. A.; Achab, Aicha; Asselin, Esther; Dabard, Marie-Pierre; Farley, Claude; Loi, Alfredo; Paris, Florentin; Wickson, Steven; Weizer, Jan (1 September 2014). "A Cenozoic-style scenario for the end-Ordovician glaciation". Nature Communications. 5 (1): 4485. Bibcode:2014NatCo...5.4485G. doi:10.1038/ncomms5485. PMC 4164773. PMID 25174941.
67. Hammarlund, Emma U.; Dahl, Tais W.; Harper, David A. T.; Bond, David P. G.; Nielsen, Arne T.; Bjerrum, Christian J.; Schovsbo, Niels H.; Schönlaub, Hans P.; Zalasiewicz, Jan A.; Canfield, Donald E. (15 May 2012). "A sulfidic driver for the end-Ordovician mass extinction". Earth and Planetary Science Letters. 331–332: 128–139. Bibcode:2012E&PSL.331..128H. doi:10.1016/j.epsl.2012.02.024. ISSN 0012-821X.
68. Jones, David S.; Fike, David A. (2013-02-01). "Dynamic sulfur and carbon cycling through the end-Ordovician extinction revealed by paired sulfate–pyrite δ34S". Earth and Planetary Science Letters. 363: 144–155. Bibcode:2013E&PSL.363..144J. doi:10.1016/j.epsl.2012.12.015. ISSN 0012-821X. Retrieved 12 August 2023.
69. Zou, Caineng; Qiu, Zhen; Wei, Hengye; Dong, Dazhong; Lu, Bin (15 December 2018). "Euxinia caused the Late Ordovician extinction: Evidence from pyrite morphology and pyritic sulfur isotopic composition in the Yangtze area, South China". Palaeogeography, Palaeoclimatology, Palaeoecology. 511: 1–11. Bibcode:2018PPP...511....1Z. doi:10.1016/j.palaeo.2017.11.033. ISSN 0031-0182. S2CID 134586047.
70. Ahm, Anne-Sofie C.; Bjerrum, Christian J.; Hammarlund, Emma U. (1 February 2017). "Disentangling the record of diagenesis, local redox conditions, and global seawater chemistry during the latest Ordovician glaciation". Earth and Planetary Science Letters. 459: 145–156. Bibcode:2017E&PSL.459..145A. doi:10.1016/j.epsl.2016.09.049. ISSN 0012-821X. Retrieved 12 August 2023.
71. Zou, Caineng; Qiu, Zhen; Poulton, Simon W.; Dong, Dazhong; Wang, Hongyan; Chen, Daizhou; Lu, Bin; Shi, Zhensheng; Tao, Huifei (2018). "Ocean euxinia and climate change "double whammy" drove the Late Ordovician mass extinction". Geology. 46 (6): 535–538. Bibcode:2018Geo....46..535Z. doi:10.1130/G40121.1. S2CID 135039656. Retrieved 12 August 2023.
72. Kozik, Nevin P.; Young, Seth A.; Newby, Sean M.; Liu, Mu; Chen, Daizhao; Hammarlund, Emma U.; Bond, David P. G.; Themii, Theodore R.; Owens, Jeremy D. (18 November 2022). "Rapid marine oxygen variability: Driver of the Late Ordovician mass extinction". Science Advances. 8 (46): eabn8345. Bibcode:2022SciA....8N8345K. doi:10.1126/sciadv.abn8345. PMC 9674285. PMID 36399571. Retrieved 12 August 2023.
73. Zhou, Lian; Algeo, Thomas J.; Shen, Jun; Hu, ZhiFang; Gong, Hongmei; Xie, Shucheng; Huang, JunHua; Gao, Shan (15 February 2015). "Changes in marine productivity and redox conditions during the Late Ordovician Hirnantian glaciation". Palaeogeography, Palaeoclimatology, Palaeoecology. 420: 223–234. Bibcode:2015PPP...420..223Z. doi:10.1016/j.palaeo.2014.12.012. ISSN 0031-0182.
74. Lu, Xinze; Kendall, Brian; Stein, Holly J.; Li, Chao; Hannah, Judith L.; Gordon, Gwyneth W.; Ebbestad, Jan Ove R. (2017-05-10). "Marine redox conditions during deposition of Late Ordovician and Early Silurian organic-rich mudrocks in the Siljan ring district, central Sweden". Chemical Geology. 457: 75–94. Bibcode:2017ChGeo.457...75L. doi:10.1016/j.chemgeo.2017.03.015. hdl:10012/13767. ISSN 0009-2541.
75. Smolarek, Justyna; Marynowski, Leszek; Trela, Wiesław; Kujawski, Piotr; Simoneit, Bernd R.T. (February 2017). "Redox conditions and marine microbial community changes during the end-Ordovician mass extinction event". Global and Planetary Change. 149: 105–122. Bibcode:2017GPC...149..105S. doi:10.1016/j.gloplacha.2017.01.002. ISSN 0921-8181.
76. Young, Seth A.; Benayoun, Emily; Kozik, Nevin P.; Hints, Olle; Martma, Tõnu; Bergström, Stig M.; Owens, Jeremy D. (15 September 2020). "Marine redox variability from Baltica during extinction events in the latest Ordovician–early Silurian" (PDF). Palaeogeography, Palaeoclimatology, Palaeoecology. 554: 109792. Bibcode:2020PPP...55409792Y. doi:10.1016/j.palaeo.2020.109792. ISSN 0031-0182. S2CID 218930512.
77. Pohl, A.; Donnadieu, Y.; Le Hir, G.; Ferreira, D. (2017). "The climatic significance of Late Ordovician-early Silurian black shales" (PDF). Paleoceanography and Paleoclimatology. 32 (4): 397–423. Bibcode:2017PalOc..32..397P. doi:10.1002/2016PA003064. ISSN 1944-9186. S2CID 6896844.
78. Finney, Stanley C.; Berry, William B. N.; Cooper, John D. (1 September 2007). "The influence of denitrifying seawater on graptolite extinction and diversification during the Hirnantian (latest Ordovician) mass extinction event". Lethaia. 40 (3): 281–291. doi:10.1111/j.1502-3931.2007.00027.x. ISSN 0024-1164. Retrieved 10 September 2023.
79. Ghienne, Jean-François; Desrochers, André; Vandenbroucke, Thijs R. A.; Achab, Aicha; Asselin, Esther; Dabard, Marie-Pierre; Farley, Claude; Loi, Alfredo; Paris, Florentin; Wickson, Steven; Veizer, Jan (2014-09-01). "A Cenozoic-style scenario for the end-Ordovician glaciation". Nature Communications. 5 (1): 4485. Bibcode:2014NatCo...5.4485G. doi:10.1038/ncomms5485. ISSN 2041-1723. PMC 4164773. PMID 25174941.
80. Bjerrum, Christian J. (2018). "Sea level, climate, and ocean poisoning by sulfide all implicated in the first animal mass extinction". Geology. 46 (6): 575–576. Bibcode:2018Geo....46..575B. doi:10.1130/focus062018.1. S2CID 134603654.
81. Bond, David P. G.; Grasby, Stephen E. (18 May 2020). "Late Ordovician mass extinction caused by volcanism, warming, and anoxia, not cooling and glaciation". Geology. 48 (8): 777–781. Bibcode:2020Geo....48..777B. doi:10.1130/G47377.1.
82. Mitchell, Charles E.; Melchin, Michael J. (11 June 2020). "Late Ordovician mass extinction caused by volcanism, warming, and anoxia, not cooling and glaciation: COMMENT". Geology. 48 (8): e509. Bibcode:2020Geo....48E.509M. doi:10.1130/G47946C.1.
83. Bartlett, Rick; Elrick, Maya; Wheeley, James R.; Polyak, Victor; Desrochers, André; Asmerom, Yemane (2018). "Abrupt global-ocean anoxia during the Late Ordovician–early Silurian detected using uranium isotopes of marine carbonates". Proceedings of the National Academy of Sciences of the United States of America. 115 (23): 5896–5901. Bibcode:2018PNAS..115.5896B. doi:10.1073/pnas.1802438115. PMC 6003337. PMID 29784792.
84. Kozik, Nevin P.; Gill, Benjamin C.; Owens, Jeremy D.; Lyons, Timothy W.; Young, Seth A. (10 January 2022). "Geochemical Records Reveal Protracted and Differential Marine Redox Change Associated With Late Ordovician Climate and Mass Extinctions". AGU Advances. 3 (1): 1–17. doi:10.1029/2021AV000563. hdl:10919/107584. ISSN 2576-604X.
85. Zhang, Tonggang; Shen, Yanan; Zhan, Renbin; Shen, Shuzhong; Chen, Xu (2009). "Large perturbations of the carbon and sulfur cycle associated with the Late Ordovician mass extinction in South China". Geology. 37 (4): 299–302. Bibcode:2009Geo....37..299Z. doi:10.1130/G25477A.1.
86. Liu, Mu; Chen, Daizhao; Jiang, Lei; Stockey, Richard G.; Aseal, Dan; Zhang, Bao; Liu, Kang; Yang, Xiangrong; Yan, Detian; Planavsky, Noah J. (15 July 2022). "Oceanic anoxia and extinction in the latest Ordovician". Earth and Planetary Science Letters. 588. doi:10.1016/j.epsl.2022.117553. S2CID 248681972. Retrieved 25 May 2023.
87. Yang, Xiangrong; Yan, Detian; Li, Tong; Zhang, Liwei; Zhang, Bao; He, Jie; Fan, Haoyuan; Shangguan, Yunfei (April 2020). "Oceanic environment changes caused the Late Ordovician extinction: evidence from geochemical and Nd isotopic composition in the Yangtze area, South China". Geological Magazine. 157 (4): 651–665. Bibcode:2020GeoM..157..651Y. doi:10.1017/S0016756819001237. ISSN 0016-7568. S2CID 210259392.
88. Men, Xin; Mou, Chuanlong; Ge, Xiangying (1 August 2022). "Changes in palaeoclimate and palaeoenvironment in the Upper Yangtze area (South China) during the Ordovician–Silurian transition". Scientific Reports. 12 (1): 13186. Bibcode:2022NatSR..1213186M. doi:10.1038/s41598-022-17105-2. PMC 9343391. PMID 35915216.
89. Qiu, Zhen; Wei, Hengye; Tian, Li; Dal Corso, Jacopo; Zhang, Jiaqiang; Zou, Caineng (25 March 2022). "Different controls on the Hg spikes linked the two pulses of the Late Ordovician mass extinction in South China". Scientific Reports. 12 (1): 5195. doi:10.1038/s41598-022-08941-3. PMC 8956570. PMID 35338189.
90. Pohl, Alexandre; Lu, Zunli; Lu, Wanyi; Stockey, Richard G.; Elrick, Maya; Li, Menghan; Desrochers, André; Shen, Yanan; He, Ruliang; Finnegan, Seth; Ridgwell, Andy (1 November 2021). "Vertical decoupling in Late Ordovician anoxia due to reorganization of ocean circulation". Nature Geoscience. 14 (11): 868–873. Bibcode:2021NatGe..14..868P. doi:10.1038/s41561-021-00843-9. S2CID 240358402. Retrieved 22 October 2022.
91. Luo, Genming; Algeo, Thomas J.; Zhan, Renbin; Yan, Detian; Huang, Junhua; Liu, Jiangsi; Xie, Shucheng (15 April 2016). "Perturbation of the marine nitrogen cycle during the Late Ordovician glaciation and mass extinction". Palaeogeography, Palaeoclimatology, Palaeoecology. Ecosystem evolution in deep time: evidence from the rich Palaeozoic fossil records of China. 448: 339–348. Bibcode:2016PPP...448..339L. doi:10.1016/j.palaeo.2015.07.018. ISSN 0031-0182.
92. Koehler, Matthew C.; Stüeken, Eva E.; Hillier, Stephen; Prave, Anthony R. (15 November 2019). "Limitation of fixed nitrogen and deepening of the carbonate-compensation depth through the Hirnantian at Dob's Linn, Scotland". Palaeogeography, Palaeoclimatology, Palaeoecology. 534: 109321. Bibcode:2019PPP...53409321K. doi:10.1016/j.palaeo.2019.109321. hdl:10023/20447. ISSN 0031-0182. S2CID 202191446.
93. Liu, Yu; Li, Chao; Fan, Junxuan; Peng, Ping’an; Algeo, Thomas J. (15 September 2020). "Elevated marine productivity triggered nitrogen limitation on the Yangtze Platform (South China) during the Ordovician-Silurian transition". Palaeogeography, Palaeoclimatology, Palaeoecology. 554: 109833. Bibcode:2020PPP...55409833L. doi:10.1016/j.palaeo.2020.109833. ISSN 0031-0182. S2CID 219934128.
94. Wu, Xuejin; Luo, Hui; Zhang, Junpeng; Chen, Qing; Fang, Xiang; Wang, Wenhui; Li, Wenjie; Shi, Zhensheng; Zhang, Yuandong (1 September 2023). "Volcanism-driven marine eutrophication in the end-Ordovician: Evidence from radiolarians and trace elements of black shale in South China". Journal of Asian Earth Sciences. 253: 105687. doi:10.1016/j.jseaes.2023.105687. S2CID 258402989. Retrieved 10 September 2023.
95. Wang, Guangxu; Zhan, Renbin; Percival, Ian G. (May 2019). "The end-Ordovician mass extinction: A single-pulse event?". Earth-Science Reviews. 192: 15–33. Bibcode:2019ESRv..192...15W. doi:10.1016/j.earscirev.2019.01.023. ISSN 0012-8252. S2CID 134266940.
96. Lu, Xinze; Gilleaudeau, Geoffrey J.; Kendall, Brian (1 January 2024). "Uranium isotopes in non-euxinic shale and carbonate reveal dynamic Katian marine redox conditions accompanying a decrease in biodiversity prior to the Late Ordovician Mass Extinction". Geochimica et Cosmochimica Acta. 364: 22–43. doi:10.1016/j.gca.2023.10.034. ISSN 0016-7037. S2CID 264988361. Retrieved 11 December 2023 – via Elsevier Science Direct.
97. Smolarek-Lach, Justyna; Marynowski, Leszek; Trela, Wiesław; Wignall, Paul B. (28 February 2019). "Mercury Spikes Indicate a Volcanic Trigger for the Late Ordovician Mass Extinction Event: An Example from a Deep Shelf of the Peri-Baltic Region". Scientific Reports. 9 (1): 3139. Bibcode:2019NatSR...9.3139S. doi:10.1038/s41598-019-39333-9. PMC 6395715. PMID 30816186.
98. Katz, Cheryl (2015-09-11). . National Geographic News. Archived from the original on September 13, 2015. Retrieved 2015-09-12.
99. Vandenbroucke, Thijs R. A.; Emsbo, Poul; Munnecke, Axel; Nuns, Nicolas; Duponchel, Ludovic; Lepot, Kevin; Quijada, Melesio; Paris, Florentin; Servais, Thomas (2015-08-25). "Metal-induced malformations in early Palaeozoic plankton are harbingers of mass extinction". Nature Communications. 6. Article 7966. Bibcode:2015NatCo...6.7966V. doi:10.1038/ncomms8966. PMC 4560756. PMID 26305681.
100. Ball, Philip (24 September 2003). "Gamma-ray burst linked to mass extinction". Nature. doi:10.1038/news030922-7. ISSN 1476-4687.
101. Melott, Adrian L.; Thomas, Brian C.; Hogan, Daniel P.; Ejzak, Larissa M.; Jackman, Charles H. (21 July 2005). "Climatic and biogeochemical effects of a galactic gamma ray burst". Geophysical Research Letters. 32 (14). arXiv:astro-ph/0503625. Bibcode:2005GeoRL..3214808M. doi:10.1029/2005GL023073. S2CID 6150230. Retrieved 21 August 2022.
102. Melott, A.L.; et al. (2004). "Did a gamma-ray burst initiate the late Ordovician mass extinction?". International Journal of Astrobiology. 3 (2): 55–61. arXiv:astro-ph/0309415. Bibcode:2004IJAsB...3...55M. doi:10.1017/S1473550404001910. S2CID 13124815.
103. "Ray burst is extinction suspect". BBC. April 6, 2005. Retrieved 2008-04-30.
104. Melott, A.L. & Thomas, B.C. (2009). "Late Ordovician geographic patterns of extinction compared with simulations of astrophysical ionizing radiation damage". Paleobiology. 35 (3): 311–320. arXiv:0809.0899. Bibcode:2009Pbio...35..311M. doi:10.1666/0094-8373-35.3.311. S2CID 11942132.
105. Rodríguez-López, Lien; Cardenas, Rolando; González-Rodríguez, Lisdelys; Guimarais, Mayrene; Horvath, Jorge (24 January 2021). "Influence of a galactic gamma ray burst on ocean plankton". Astronomical Notes. 342 (1–2): 45–48. arXiv:2011.08433. Bibcode:2021AN....342...45R. doi:10.1002/asna.202113878. S2CID 226975864. Retrieved 21 October 2022.
106. Thomas, Brian C.; Jackman, Charles H.; Melott, Adrian L.; Laird, Claude M.; Stolarski, Richard S.; Gehrels, Neil; Cannizzo, John K.; Hogan, Daniel P. (28 February 2005). "Terrestrial Ozone Depletion due to a Milky Way Gamma-Ray Burst". The Astrophysical Journal. 622 (2): L153–L156. arXiv:astro-ph/0411284. Bibcode:2005ApJ...622L.153T. doi:10.1086/429799. hdl:2060/20050179464. S2CID 11199820. Retrieved 22 October 2022.
107. Thomas, Brian C.; Melott, Adrian L.; Jackman, Charles H.; Laird, Claude M.; Medvedev, Mikhail V.; Stolarski, Richard S.; Gehrels, Neil; Cannizzo, John K.; Hogan, Daniel P.; Ejzak, Larissa M. (20 November 2005). "Gamma-Ray Bursts and the Earth: Exploration of Atmospheric, Biological, Climatic, and Biogeochemical Effects". The Astrophysical Journal. 634 (1): 509–533. arXiv:astro-ph/0505472. Bibcode:2005ApJ...634..509T. doi:10.1086/496914. S2CID 2046052. Retrieved 22 October 2022.
108. Hu, Dongping; Li, Menghan; Zhang, Xiaolin; Turchyn, Alexandra V.; Gong, Yizhe; Shen, Yanan (8 May 2020). "Large mass-independent sulphur isotope anomalies link stratospheric volcanism to the Late Ordovician mass extinction". Nature Communications. 11 (1): 2297. doi:10.1038/s41467-020-16228-2. ISSN 2041-1723. PMC 7210970. PMID 32385286. S2CID 218540475. Retrieved 14 August 2023.
109. Hall, Shannon (10 June 2020). "Familiar Culprit May Have Caused Mysterious Mass Extinction - A planet heated by giant volcanic eruptions drove the earliest known wipeout of life on Earth". The New York Times. Retrieved 15 June 2020.
110. Derakhshi, Morteza; Ernst, Richard E.; Kamo, Sandra L. (July 2022). "Ordovician-Silurian volcanism in northern Iran: Implications for a new Large Igneous Province (LIP) and a robust candidate for the Late Ordovician mass extinction". Gondwana Research. 107: 256–280. Bibcode:2022GondR.107..256D. doi:10.1016/j.gr.2022.03.009. S2CID 247653339. Retrieved 19 October 2022.
111. Rasmussen, Christian M. Ø; Kröger, Björn; Nielsen, Morten L.; Colmenar, Jorge (2019-04-09). "Cascading trend of Early Paleozoic marine radiations paused by Late Ordovician extinctions". Proceedings of the National Academy of Sciences of the United States of America. 116 (15): 7207–7213. Bibcode:2019PNAS..116.7207R. doi:10.1073/pnas.1821123116. ISSN 0027-8424. PMC 6462056. PMID 30910963.
112. Fan, Jun-xuan; Shen, Shu-zhong; Erwin, Douglas H.; Sadler, Peter M.; MacLeod, Norman; Cheng, Qiu-ming; Hou, Xu-dong; Yang, Jiao; Wang, Xiang-dong; Wang, Yue; Zhang, Hua (17 January 2020). "A high-resolution summary of Cambrian to Early Triassic marine invertebrate biodiversity". Science. 367 (6475): 272–277. Bibcode:2020Sci...367..272F. doi:10.1126/science.aax4953. PMID 31949075. S2CID 210698603.
113. Deng, Yiying; Fan, Junxuan; Zhang, Shuhan; Fang, Xiang; Chen, Zhongyang; Shi, Yukun; Wang, Haiwen; Wang, Xinbing; Yang, Jiao; Hou, Xudong; Wang, Yue (2021-09-01). "Timing and patterns of the Great Ordovician Biodiversification Event and Late Ordovician mass extinction: Perspectives from South China". Earth-Science Reviews. 220: 103743. Bibcode:2021ESRv..22003743D. doi:10.1016/j.earscirev.2021.103743. ISSN 0012-8252.
114. Cherns, Lesley; Wheeley, James R. (8 August 2007). "A pre-Hirnantian (Late Ordovician) interval of global cooling – The Boda event re-assessed". Palaeogeography, Palaeoclimatology, Palaeoecology. 251 (3): 449–460. doi:10.1016/j.palaeo.2007.04.010. ISSN 0031-0182. Retrieved 10 September 2023.
115. Wang, Yanjun; Wang, Bo; Li, Ming; Cao, Shengnan; Wang, Hongbin; Pan, Shuxin; Guo, Juanjuan; Ma, Delong; Song, Fang; Cao, Tingting; Safonova, Inna Y.; Zhong, Linglin; Ni, Xinghua (15 August 2022). "New constraints on volcanism during Ordovician-Silurian transition: Insights from marine bentonites in northern Yili Block (NW China)". Palaeogeography, Palaeoclimatology, Palaeoecology. 600: 111073. Bibcode:2022PPP...60011073W. doi:10.1016/j.palaeo.2022.111073. S2CID 249003502. Retrieved 26 December 2022.
116. Jia, Jixin; Du, Xuebin; Zhao, Ke; Ma, Zhengyang (15 June 2023). "Different integrated mechanisms drove the two pulses of the Late Ordovician mass extinction". Palaeogeography, Palaeoclimatology, Palaeoecology. 620: 111572. doi:10.1016/j.palaeo.2023.111572. ISSN 0031-0182. S2CID 258235044. Retrieved 11 December 2023 – via Elsevier Science Direct.
117. Lu, Yangbo; Shen, Jun; Wang, Yuxuan; Lu, Yongchao; Algeo, Thomas J.; Jiang, Shu; Yang, Detian; Gou, Qiyang (1 September 2022). "Seawater sources of Hg enrichment in Ordovician-Silurian boundary strata, South China". Palaeogeography, Palaeoclimatology, Palaeoecology. 601: 111156. Bibcode:2022PPP...60111156L. doi:10.1016/j.palaeo.2022.111156. S2CID 251029419. Retrieved 26 December 2022.
118. Shen, Jun; Algeo, Thomas J.; Chen, Jiubin; Planavsky, Noah J.; Feng, Qinglai; Yu, Jianxin; Liu, Jinling (1 April 2019). "Mercury in marine Ordovician/Silurian boundary sections of South China is sulfide-hosted and non-volcanic in origin". Earth and Planetary Science Letters. 511: 130–140. Bibcode:2019E&PSL.511..130S. doi:10.1016/j.epsl.2019.01.028. S2CID 133689085. Retrieved 29 March 2023.
119. Liu, Yu; Li, Yuanchun; Hou, Mingcai; Shen, Jun; Algeo, Thomas J.; Fan, Junxuan; Zhou, Xiaolin; Chen, Qing; Sun, Zongyuan; Li, Chao (January 2023). "Terrestrial rather than volcanic mercury inputs to the Yangtze Platform (South China) during the Ordovician-Silurian transition". Global and Planetary Change. 220. doi:10.1016/j.gloplacha.2022.104023. S2CID 255019480. Retrieved 12 August 2023.
120. Glikson, Andrew (9 August 2023). "New evidence suggests the world's largest known asteroid impact structure is buried deep in southeast Australia". theconversation.com. The Conversation US, Inc. Retrieved 2 September 2023. Hidden traces of Earth's early history

Further reading

• Gradstein, Felix M.; Ogg, James G.; Smith, Alan G. (2004). A Geological Time Scale 2004 (3rd ed.). Cambridge University Press: Cambridge University Press. ISBN 9780521786737.
• Hallam, Anthony; Paul B., Wignall (1997). Mass Extinctions and Their Aftermath. Oxford University Press. ISBN 9780191588396.
• Webby, Barry D.; Paris, Florentin; Droser, Mary L.; Percival, Ian G, eds. (2004). The great Ordovician biodiversification event. New York: Columbia University Press. ISBN 9780231501637.

External links

• Jacques Veniers, "The end-Ordovician extinction event": abstract of Hallam and Wignall, 1997.