Extinction Events
Mass Extinctions of Life on Earth
Mass extinctions on Earth tend to be associated with the rapid and large scale loss of animal life on the planet. There is less evidence that these mass extinction coincide with the large-scale loss of plant groups, with the possible exception of the Late Permian Extinction (Silvestro et al. 2014)
Research indicates that mass extinctions are closely correlated with Large Igneous Province volcanism , including the 16 large and small mass extinctions that have occurred over the last 541 million years (Rampino et al. 2023)
Modern Mass Extinction
Time period: Holocene epoch (11, 700 years before present until today)
Description: Rapid loss of plant and animal species due to human activities
Cause: Expansion and activities of Homo sapiens on Earth, including pollution, overpopulation, and increased carbon output.
End of Cretaceous Mass Extinction
Last of the "big six extinctions", and most recent extinction event
Time period: 66 Ma
Description: Evidence of global disruption of plant communities at the K–T boundary ((Vivi, Raine, and Hollis 2001; Wilf and Johnson 2004; Nichols and Johnson 2008).
Extinctions are seen both in studies of fossil pollen, and fossil leaves.
In North America, the data suggest massive devastation and mass extinction of plants at the K–T boundary sections; approximately 57% of plant species became extinct.
In high southern hemisphere latitudes, such as New Zealand and Antarctica the mass die-off of flora caused no significant turnover in species, but dramatic and short-term changes in the relative abundance of plant groups.
Cause: Chicxulub meteorite impact and(?) large scale volcanism
Research by Cox and Keller (2023) suggested that the outpouring of climate-altering gases from the Deccan Traps alone could have been sufficient to trigger the global extinction
The Traps had been erupting for roughly 300,000 years before the Chicxulub asteroid
End of Triassic Mass Extinction
Fifth of the "big six extinctions"
Time period: 201 Ma
Description: >95 percent species-level turnover of Triassic-Jurassic megaflora (McElwain, Beerling, and Woodward 1999)
Cause: There are many unknown aspects to the cause of this extinction event
Evidence indicates a fourfold increase in atmospheric carbon dioxide concentration and suggests an associated 3° to 4°C “greenhouse” warming across the boundary, possibly due to volcanism
These environmental conditions are calculated to have raised leaf temperatures above a highly conserved lethal limit
Climate extremes went back and forth unpredictably, making equatorial environments difficult for new species to establish.
In the seas, a whole class (conodonts) and 34% of marine genera disappeared.
On land, all archosaurs other than crocodylomorphs (Sphenosuchia and Crocodyliformes) and Avemetatarsalia (pterosaurs and dinosaurs), some remaining therapsids, and many of the large amphibians became extinct.
End of Permian Mass Extinction
Largest extinction event in Earth's history; Fourth of the "big six extinctions"
Time period: 252 Ma; length was less than 1 Ma, probably much less than 300 Ka
Description: Extinction of 96% of ocean species; ~70% of terrestrial life
Cause(s):
Coincides with the largest flood basalt of Phanerozic (Siberian Traps), in which massive amounts of lava spewed, equaling half of the size of the United States
Volcanoes released large amount of carbon dioxide into atmosphere, leading to extreme global warming, which may have led to major anoxic pulse on both land and sea, and possibly associated with major pulse of hypercapnia (high carbon dioxide levels) in sea
Global warming would melt the deep sea ices (clathrates) rich in methane, which would greatly increase greenhouse effect (methane a stronger greenhouse gas than carbon dioxide), thus creating a positive feedback loop, clathrate-driven global warming would melt more clathrates, and so on...
New evidence suggests changes in methagen Archaea physiology released methane at greater rates causing global warming.
Some evidence suggests a "burp" of hydrogen sulfide, perhaps due to blooms of hydrogen sulfide bacteria in anoxic deep water, which would have the additional effect of destroying ozone layer, adding UV radiation damage to the mix.
Mid-Permian Mass Extinction
Third of the "big six extinctions"
Time period: 259 Ma
Description: ~40% to 50% marine genera disappear as well as transition in terrestrial flora
The scale-tree dominated swamp forests of the Carboniferous and early Permian were replaced by "seed ferns" and early conifers
Cause: Anoxia and acidification possible due to heavy volcanism with disruption of the carbon cycle
End of Devonian Mass Extinction
Second of the "big six extinctions"
Time period: Late Devonian (372 Ma)
Description: Toward the end of the land plant radiation, the Earth experienced an ice age.
Cause: Increase in plant biomass, and coincident photosynthesis, caused a draw-down of atmospheric carbon dioxide
Loss of carbon dioxide in atmosphere results in global cooling and glaciation.
"Biotic crisis" decimates tropical marine environments (Algeo and Sheckler 1998)
Land plants may have increased weathering of rocks and soils, producing an influx of minerals to the marine env't
Both an increase in root depth and penetration as well as the ability of seed plants to conoloize drier, upland env'ts may have contributed to increased soil formation (pedogenesis)
Increased nutrient input on rivers creates eutrophic conditions in continental seaways, "resulting in algal blooms, widespread bottom water anoxia, and high sedimentary organic carbon fluxes".
Volcanic eruptions have also cited as a cause of the mass extinction (Racki et al. 2018)
This event is also correlated with a smaller (52 km diameter) Siljan impact crater in Sweden, dating to 376 ± 4 Ma (Reimold et al. 2005)
End of Ordovician Mass Extinction
2nd largest Phanerozoic extinction event; first of the "big six extinctions"
Time period: Late Ordovician (444 Ma)
End of Katian event, and end of Hirantian event
Each glaciation thought to last between 0.5-1.5 Ma
Description: Several glaciation events causing the extinction of 50-60% of marine life.
Cause: Drop in CO2 levels cause glaciations events
Sea levels frequently rise and fall during these glaciations
Volcanic activity created silicates that absorbed CO2 from the atmosphere
Carbon dioxide levels dropped from 7,000 ppm to 4,400 ppm
Appearance of early land plants (bryophytes) may have triggered the 2nd largest glaciation event (Lenton et al. 2012, Retallack 2015)
Increased weathering of rocks that absorb carbon dioxide levels
Carbon is buried in deep sea sediments dropping global CO2 levels
The latest Ordovician was a period of widespread ocean anoxia and black-shale deposition,, high atmospheric CO2, and global warming (e.g., Wang et al., 1993; Underwood et al., 1997; Pohl et al., 2017; Smolarek-Lach et al., 130 2019; Bond and Grasby, 2020; Bond and Sun, 2021).
End of Ediacaran Mass Extinction
Time period: Late Ediacaran Period (~541 Ma)
Description: A mass extinction of acritarchs, and the sudden disappearance of the Ediacara biota and calcifying organisms
Cause: The emergence of animals (metazoans) may have altered the environment, causing the extinction of Ediacarans
