An extinction event (also known as a mass extinction or biotic crisis)
is a widespread and rapid decrease in the biodiversity on Earth. Such
an event is identified by a sharp change in the diversity and
abundance of multicellular organisms. It occurs when the rate of
extinction increases with respect to the rate of speciation. Because
most diversity and biomass on
Earth is microbial, and thus difficult
to measure, recorded extinction events affect the easily observed,
biologically complex component of the biosphere rather than the total
diversity and abundance of life.
Extinction occurs at an uneven rate. Based on the fossil record, the
background rate of extinctions on
Earth is about two to five taxonomic
families of marine animals every million years. Marine fossils are
mostly used to measure extinction rates because of their superior
fossil record and stratigraphic range compared to land animals.
Great Oxygenation Event
Great Oxygenation Event was probably the first major extinction
event. Since the
Cambrian explosion five further major mass
extinctions have significantly exceeded the background extinction
rate. The most recent and arguably best-known, the
Paleogene extinction event, which occurred approximately
66 million years ago (Ma), was a large-scale mass extinction of animal
and plant species in a geologically short period of time. In
addition to the five major mass extinctions, there are numerous minor
ones as well, and the ongoing mass extinction caused by human activity
is sometimes called the sixth extinction. Mass extinctions seem to
be a mainly
Phanerozoic phenomenon, with extinction rates low before
large complex organisms arose.
Estimates of the number of major mass extinctions in the last 540
million years range from as few as five to more than twenty. These
differences stem from the threshold chosen for describing an
extinction event as "major", and the data chosen to measure past
1 Major extinction events
2 List of extinction events
3 Evolutionary importance
4 Patterns in frequency
5.1 Identifying causes of particular mass extinctions
5.2 Most widely supported explanations
Flood basalt events
5.2.2 Sea-level falls
5.2.3 Impact events
5.2.4 Global cooling
5.2.5 Global warming
5.2.6 Clathrate gun hypothesis
5.2.7 Anoxic events
Hydrogen sulfide emissions from the seas
5.2.9 Oceanic overturn
5.2.10 A nearby nova, supernova or gamma ray burst
5.2.11 Geomagnetic reversal
5.2.12 Plate tectonics
5.2.13 Other hypotheses
5.2.14 Future biosphere extinction
6 Effects and recovery
7 See also
10 External links
Major extinction events
Badlands near Drumheller, Alberta, where erosion has exposed the
Trilobites were highly successful marine animals until the
Triassic extinction event wiped them all out
In a landmark paper published in 1982,
Jack Sepkoski and David M. Raup
identified five mass extinctions. They were originally identified as
outliers to a general trend of decreasing extinction rates during the
Phanerozoic, but as more stringent statistical tests have been
applied to the accumulating data, it has been established that
multicellular animal life has experienced five major and many minor
mass extinctions. The "Big Five" cannot be so clearly defined, but
rather appear to represent the largest (or some of the largest) of a
relatively smooth continuum of extinction events.
Silurian extinction events (End
Ordovician or O–S):
450–440 Ma at the Ordovician–
Silurian transition. Two events
occurred that killed off 27% of all families, 57% of all genera and
60% to 70% of all species. Together they are ranked by many
scientists as the second largest of the five major extinctions in
Earth's history in terms of percentage of genera that became extinct.
Devonian extinction: 375–360 Ma near the
Carboniferous transition. At the end of the
Frasnian Age in
the later part(s) of the
Devonian Period, a prolonged series of
extinctions eliminated about 19% of all families, 50% of all genera
and at least 70% of all species. This extinction event lasted
perhaps as long as 20 million years, and there is evidence for a
series of extinction pulses within this period.
Triassic extinction event (End Permian): 252 Ma at the
Triassic transition. Earth's largest extinction killed
57% of all families, 83% of all genera and 90% to 96% of all
species (53% of marine families, 84% of marine genera, about 96% of
all marine species and an estimated 70% of land species, including
insects). The highly successful marine arthropod, the trilobite
became extinct. The evidence regarding plants is less clear, but new
taxa became dominant after the extinction. The "Great Dying" had
enormous evolutionary significance: on land, it ended the primacy of
mammal-like reptiles. The recovery of vertebrates took 30 million
years, but the vacant niches created the opportunity for
archosaurs to become ascendant. In the seas, the percentage of animals
that were sessile dropped from 67% to 50%. The whole late
a difficult time for at least marine life, even before the "Great
Jurassic extinction event (End Triassic): 201.3 Ma at
Jurassic transition. About 23% of all families, 48% of
all genera (20% of marine families and 55% of marine genera) and 70%
to 75% of all species became extinct. Most non-dinosaurian
archosaurs, most therapsids, and most of the large amphibians were
eliminated, leaving dinosaurs with little terrestrial competition.
Non-dinosaurian archosaurs continued to dominate aquatic environments,
while non-archosaurian diapsids continued to dominate marine
Temnospondyl lineage of large amphibians also
survived until the
Cretaceous in Australia (e.g., Koolasuchus).
Paleogene extinction event (End Cretaceous, K–Pg
extinction, or formerly K–T extinction): 66 Ma at the Cretaceous
Paleogene (Danian) transition interval. The
event formerly called the Cretaceous-Tertiary or K–T extinction or
K–T boundary is now officially named the Cretaceous–
K–Pg) extinction event. About 17% of all families, 50% of all
genera and 75% of all species became extinct. In the seas all
the ammonites, plesiosaurs and mosasaurs disappeared and the
percentage of sessile animals (those unable to move about) was reduced
to about 33%. All non-avian dinosaurs became extinct during that
time. The boundary event was severe with a significant amount of
variability in the rate of extinction between and among different
clades. Mammals and birds, the latter descended from theropod
dinosaurs, emerged as dominant large land animals.
Despite the popularization of these five events, there is no definite
line separating them from other extinction events; using different
methods of calculating an extinction's impact can lead to other events
featuring in the top five.
The older the fossil record gets, the more difficult it is to read.
This is because:
Older fossils are harder to find as they are usually buried at a
Dating older fossils is more difficult.
Productive fossil beds are researched more than unproductive ones,
therefore leaving certain periods unresearched.
Prehistoric environmental events can disturb the deposition process.
The preservation of fossils varies on land, but marine fossils tend to
be better preserved than their sought after land-based
It has been suggested that the apparent variations in marine
biodiversity may actually be an artifact, with abundance estimates
directly related to quantity of rock available for sampling from
different time periods. However, statistical analysis shows that
this can only account for 50% of the observed pattern,[citation
needed] and other evidence (such as fungal spikes)[clarification
needed] provides reassurance that most widely accepted extinction
events are real. A quantification of the rock exposure of Western
Europe indicates that many of the minor events for which a biological
explanation has been sought are most readily explained by sampling
Research completed after the seminal 1982 paper has concluded that a
sixth mass extinction event is ongoing:
6. Holocene extinction: Currently ongoing. Extinctions have occurred
at over 1000 times the background extinction rate since 1900.
The mass extinction is considered a result of human
More recent research has indicated that the End-Capitanian extinction
event likely constitutes a separate extinction event from the
Triassic extinction event; if so, it would be larger than
many of the "Big Five" extinction events.
List of extinction events
This is a list of extinction events:
Period or supereon
c. 10,000 BCE — Ongoing
Quaternary extinction event
640,000, 74,000, and 13,000 years
Unknown; may include climate changes and human overhunting
Pliocene–Pleistocene boundary extinction
Supernova? Eltanin impact?
Middle Miocene disruption
– climate change due to change of ocean circulation patterns and
perhaps related to the Milankovitch cycles?.
Eocene–Oligocene extinction event
Paleogene extinction event
Cenomanian-Turonian boundary event
Caribbean large igneous province
Jurassic (Tithonian) extinction
Jurassic extinction event
Central Atlantic magmatic province; impactor
Carnian Pluvial Event
Wrangellia flood basalts
Triassic extinction event
Siberian Traps; Wilkes Land Crater;Anoxic event
End-Capitanian extinction event
Carboniferous rainforest collapse
Changes in sea level and chemistry?
Global drop in sea level?
Deep-ocean anoxia; Milankovitch cycles?
Silurian extinction events
Global cooling and sea level drop; Gamma-ray burst?
Ordovician extinction event
Dresbachian extinction event
End-Botomian extinction event
Great Oxygenation Event
Rising oxygen levels in the atmosphere due to the development of
view • discuss • edit
Earliest sexual reproduction
Axis scale: million years
Orange labels: ice ages.
Human timeline and Nature timeline
Mass extinctions have sometimes accelerated the evolution of life on
Earth. When dominance of particular ecological niches passes from one
group of organisms to another, it is rarely because the new dominant
group is "superior" to the old and usually because an extinction event
eliminates the old dominant group and makes way for the new
For example, mammaliformes ("almost mammals") and then mammals existed
throughout the reign of the dinosaurs, but could not compete for the
large terrestrial vertebrate niches which dinosaurs monopolized. The
Cretaceous mass extinction removed the non-avian dinosaurs and
made it possible for mammals to expand into the large terrestrial
vertebrate niches. Ironically, the dinosaurs themselves had been
beneficiaries of a previous mass extinction, the end-Triassic, which
eliminated most of their chief rivals, the crurotarsans.
Another point of view put forward in the Escalation hypothesis
predicts that species in ecological niches with more
organism-to-organism conflict will be less likely to survive
extinctions. This is because the very traits that keep a species
numerous and viable under fairly static conditions become a burden
once population levels fall among competing organisms during the
dynamics of an extinction event.
Furthermore, many groups which survive mass extinctions do not recover
in numbers or diversity, and many of these go into long-term decline,
and these are often referred to as "Dead Clades Walking".
Darwin was firmly of the opinion that biotic interactions, such as
competition for food and space—the ‘struggle for
existence’—were of considerably greater importance in promoting
evolution and extinction than changes in the physical environment. He
expressed this in The Origin of Species: "Species are produced and
exterminated by slowly acting causes…and the most import of all
causes of organic change is one which is almost independent of
altered…physical conditions, namely the mutual relation of organism
to organism-the improvement of one organism entailing the improvement
or extermination of others".
Patterns in frequency
It has been suggested variously that extinction events occurred
periodically, every 26 to 30 million years, or that
diversity fluctuates episodically every ~62 million years. Various
ideas attempt to explain the supposed pattern, including the presence
of a hypothetical companion star to the sun, oscillations in
the galactic plane, or passage through the Milky Way's spiral
arms. However, other authors have concluded the data on marine
mass extinctions do not fit with the idea that mass extinctions are
periodic, or that ecosystems gradually build up to a point at which a
mass extinction is inevitable. Many of the proposed correlations
have been argued to be spurious. Others have argued that there
is strong evidence supporting periodicity in a variety of records,
and additional evidence in the form of coincident periodic variation
in nonbiological geochemical variables.
"Big Five" mass extinctions
Other mass extinctions
Million years ago
Thousands of genera
Phanerozoic biodiversity as shown by the fossil record
Mass extinctions are thought to result when a long-term stress is
compounded by a short term shock. Over the course of the
Phanerozoic, individual taxa appear to be less likely to become
extinct at any time, which may reflect more robust food webs as
well as less extinction-prone species and other factors such as
continental distribution. However, even after accounting for
sampling bias, there does appear to be a gradual decrease in
extinction and origination rates during the Phanerozoic. This may
represent the fact that groups with higher turnover rates are more
likely to become extinct by chance; or it may be an artefact of
taxonomy: families tend to become more speciose, therefore less prone
to extinction, over time; and larger taxonomic groups (by
definition) appear earlier in geological time.
It has also been suggested that the oceans have gradually become more
hospitable to life over the last 500 million years, and thus less
vulnerable to mass extinctions,[note 1] but susceptibility to
extinction at a taxonomic level does not appear to make mass
extinctions more or less probable.
There is still debate about the causes of all mass extinctions. In
general, large extinctions may result when a biosphere under long-term
stress undergoes a short-term shock. An underlying mechanism
appears to be present in the correlation of extinction and origination
rates to diversity. High diversity leads to a persistent increase in
extinction rate; low diversity to a persistent increase in origination
rate. These presumably ecologically controlled relationships likely
amplify smaller perturbations (asteroid impacts, etc.) to produce the
global effects observed.
Identifying causes of particular mass extinctions
A good theory for a particular mass extinction should: (i) explain all
of the losses, not just focus on a few groups (such as dinosaurs);
(ii) explain why particular groups of organisms died out and why
others survived; (iii) provide mechanisms which are strong enough to
cause a mass extinction but not a total extinction; (iv) be based on
events or processes that can be shown to have happened, not just
inferred from the extinction.
It may be necessary to consider combinations of causes. For example,
the marine aspect of the end-
Cretaceous extinction appears to have
been caused by several processes which partially overlapped in time
and may have had different levels of significance in different parts
of the world.
Arens and West (2006) proposed a "press / pulse" model in which mass
extinctions generally require two types of cause: long-term pressure
on the eco-system ("press") and a sudden catastrophe ("pulse") towards
the end of the period of pressure. Their statistical analysis of
marine extinction rates throughout the
Phanerozoic suggested that
neither long-term pressure alone nor a catastrophe alone was
sufficient to cause a significant increase in the extinction rate.
Most widely supported explanations
Macleod (2001) summarized the relationship between mass
extinctions and events which are most often cited as causes of mass
extinctions, using data from Courtillot et al. (1996), Hallam
(1992) and Grieve et al. (1996):
Flood basalt events: 11 occurrences, all associated with significant
extinctions But Wignall (2001) concluded that only five of the
major extinctions coincided with flood basalt eruptions and that the
main phase of extinctions started before the eruptions.
Sea-level falls: 12, of which seven were associated with significant
Asteroid impacts: one large impact is associated with a mass
extinction, i.e. the Cretaceous–
Paleogene extinction event; there
have been many smaller impacts but they are not associated with
significant extinctions.
The most commonly suggested causes of mass extinctions are listed
Flood basalt events
The formation of large igneous provinces by flood basalt events could
produced dust and particulate aerosols which inhibited photosynthesis
and thus caused food chains to collapse both on land and at sea
emitted sulfur oxides which were precipitated as acid rain and
poisoned many organisms, contributing further to the collapse of food
emitted carbon dioxide and thus possibly causing sustained global
warming once the dust and particulate aerosols dissipated.
Flood basalt events occur as pulses of activity punctuated by dormant
periods. As a result, they are likely to cause the climate to
oscillate between cooling and warming, but with an overall trend
towards warming as the carbon dioxide they emit can stay in the
atmosphere for hundreds of years.
It is speculated that massive volcanism caused or contributed to the
Triassic and End-
Cretaceous extinctions. The
correlation between gigantic volcanic events expressed in the large
igneous provinces and mass extinctions was shown for the last 260
Myr. Recently such possible correlation was extended for the
These are often clearly marked by worldwide sequences of
contemporaneous sediments which show all or part of a transition from
sea-bed to tidal zone to beach to dry land – and where there is no
evidence that the rocks in the relevant areas were raised by
geological processes such as orogeny. Sea-level falls could reduce the
continental shelf area (the most productive part of the oceans)
sufficiently to cause a marine mass extinction, and could disrupt
weather patterns enough to cause extinctions on land. But sea-level
falls are very probably the result of other events, such as sustained
global cooling or the sinking of the mid-ocean ridges.
Sea-level falls are associated with most of the mass extinctions,
including all of the "Big Five"—End-Ordovician, Late Devonian,
End-Permian, End-Triassic, and End-Cretaceous.
A study, published in the journal Nature (online June 15, 2008)
established a relationship between the speed of mass extinction events
and changes in sea level and sediment. The study suggests changes
in ocean environments related to sea level exert a driving influence
on rates of extinction, and generally determine the composition of
life in the oceans.
The impact of a sufficiently large asteroid or comet could have caused
food chains to collapse both on land and at sea by producing dust and
particulate aerosols and thus inhibiting photosynthesis. Impacts
on sulfur-rich rocks could have emitted sulfur oxides precipitating as
poisonous acid rain, contributing further to the collapse of food
chains. Such impacts could also have caused megatsunamis and/or global
Most paleontologists now agree that an asteroid did hit the Earth
about 66 Ma ago, but there is an ongoing dispute whether the
impact was the sole cause of the Cretaceous–
Sustained and significant global cooling could kill many polar and
temperate species and force others to migrate towards the equator;
reduce the area available for tropical species; often make the Earth's
climate more arid on average, mainly by locking up more of the
planet's water in ice and snow. The glaciation cycles of the current
ice age are believed to have had only a very mild impact on
biodiversity, so the mere existence of a significant cooling is not
sufficient on its own to explain a mass extinction.
It has been suggested that global cooling caused or contributed to the
End-Ordovician, Permian–Triassic, Late
Devonian extinctions, and
possibly others. Sustained global cooling is distinguished from the
temporary climatic effects of flood basalt events or impacts.
This would have the opposite effects: expand the area available for
tropical species; kill temperate species or force them to migrate
towards the poles; possibly cause severe extinctions of polar species;
often make the Earth's climate wetter on average, mainly by melting
ice and snow and thus increasing the volume of the water cycle. It
might also cause anoxic events in the oceans (see below).
Global warming as a cause of mass extinction is supported by several
The most dramatic example of sustained warming is the
Paleocene–Eocene Thermal Maximum, which was associated with one of
the smaller mass extinctions. It has also been suggested to have
caused the Triassic–
Jurassic extinction event, during which 20% of
all marine families became extinct. Furthermore, the
Triassic extinction event has been suggested to have been
caused by warming.
Clathrate gun hypothesis
Main article: Clathrate gun hypothesis
Clathrates are composites in which a lattice of one substance forms a
cage around another. Methane clathrates (in which water molecules are
the cage) form on continental shelves. These clathrates are likely to
break up rapidly and release the methane if the temperature rises
quickly or the pressure on them drops quickly—for example in
response to sudden global warming or a sudden drop in sea level or
even earthquakes. Methane is a much more powerful greenhouse gas than
carbon dioxide, so a methane eruption ("clathrate gun") could cause
rapid global warming or make it much more severe if the eruption was
itself caused by global warming.
The most likely signature of such a methane eruption would be a sudden
decrease in the ratio of carbon-13 to carbon-12 in sediments, since
methane clathrates are low in carbon-13; but the change would have to
be very large, as other events can also reduce the percentage of
It has been suggested that "clathrate gun" methane eruptions were
involved in the end-
Permian extinction ("the Great Dying") and in the
Paleocene–Eocene Thermal Maximum, which was associated with one of
the smaller mass extinctions.
Anoxic events are situations in which the middle and even the upper
layers of the ocean become deficient or totally lacking in oxygen.
Their causes are complex and controversial, but all known instances
are associated with severe and sustained global warming, mostly caused
by sustained massive volcanism.
It has been suggested that anoxic events caused or contributed to the
Ordovician–Silurian, late Devonian, Permian–
Jurassic extinctions, as well as a number of lesser
extinctions (such as the Ireviken, Mulde, Lau, Toarcian and
Cenomanian–Turonian events). On the other hand, there are widespread
black shale beds from the mid-
Cretaceous which indicate anoxic events
but are not associated with mass extinctions.
The bio-availability of essential trace elements (in particular
selenium) to potentially lethal lows has been shown to coincide with,
and likely have contributed to, at least three mass extinction events
in the oceans, i.e. at the end of the Ordovician, during the Middle
and Late Devonian, and at the end of the Triassic. During periods of
low oxygen concentrations very soluble selenate (Se6+) is converted
into much less soluble selenide (Se2+), elemental Se and
Bio-availability of selenium during these
extinction events dropped to about 1% of the current oceanic
concentration, a level that has been proven lethal to many extant
Hydrogen sulfide emissions from the seas
Kump, Pavlov and Arthur (2005) have proposed that during the
Triassic extinction event the warming also upset the oceanic
balance between photosynthesising plankton and deep-water
sulfate-reducing bacteria, causing massive emissions of hydrogen
sulfide which poisoned life on both land and sea and severely weakened
the ozone layer, exposing much of the life that still remained to
fatal levels of UV radiation.
Oceanic overturn is a disruption of thermo-haline circulation which
lets surface water (which is more saline than deep water because of
evaporation) sink straight down, bringing anoxic deep water to the
surface and therefore killing most of the oxygen-breathing organisms
which inhabit the surface and middle depths. It may occur either at
the beginning or the end of a glaciation, although an overturn at the
start of a glaciation is more dangerous because the preceding warm
period will have created a larger volume of anoxic water.
Unlike other oceanic catastrophes such as regressions (sea-level
falls) and anoxic events, overturns do not leave easily identified
"signatures" in rocks and are theoretical consequences of researchers'
conclusions about other climatic and marine events.
It has been suggested that oceanic overturn caused or contributed to
Devonian and Permian–
A nearby nova, supernova or gamma ray burst
A nearby gamma-ray burst (less than 6000 light-years away) would be
powerful enough to destroy the Earth's ozone layer, leaving organisms
vulnerable to ultraviolet radiation from the Sun. Gamma ray bursts
are fairly rare, occurring only a few times in a given galaxy per
million years. It has been suggested that a supernova or gamma ray
burst caused the End-
One theory is that periods of increased geomagnetic reversals will
Earth's magnetic field
Earth's magnetic field long enough to expose the atmosphere to
the solar winds, causing oxygen ions to escape the atmosphere in a
rate increased by 3–4 orders, resulting in a disastrous decrease in
Movement of the continents into some configurations can cause or
contribute to extinctions in several ways: by initiating or ending ice
ages; by changing ocean and wind currents and thus altering climate;
by opening seaways or land bridges which expose previously isolated
species to competition for which they are poorly adapted (for example,
the extinction of most of South America's native ungulates and all of
its large metatherians after the creation of a land bridge between
North and South America). Occasionally continental drift creates a
super-continent which includes the vast majority of Earth's land area,
which in addition to the effects listed above is likely to reduce the
total area of continental shelf (the most species-rich part of the
ocean) and produce a vast, arid continental interior which may have
extreme seasonal variations.
Another theory is that the creation of the super-continent Pangaea
contributed to the End-
Permian mass extinction.
Pangaea was almost
fully formed at the transition from mid-
Permian to late-Permian, and
the "Marine genus diversity" diagram at the top of this article shows
a level of extinction starting at that time which might have qualified
for inclusion in the "Big Five" if it were not overshadowed by the
"Great Dying" at the end of the Permian.
Many other hypotheses have been proposed, such as the spread of a new
disease, or simple out-competition following an especially successful
biological innovation. But all have been rejected, usually for one of
the following reasons: they require events or processes for which
there is no evidence; they assume mechanisms which are contrary to the
available evidence; they are based on other theories which have been
rejected or superseded.
Scientists have been concerned that human activities could cause more
plants and animals to become extinct than any point in the past. Along
with human-made changes in climate (see above), some of these
extinctions could be caused by overhunting, overfishing, invasive
species, or habitat loss. A study published in May 2017 in Proceedings
of the National Academy of Sciences argued that a “biological
annihilation” akin to a sixth mass extinction event is underway as a
result of anthropogenic causes, such as over-population and
over-consumption. The study suggested that as much as 50% of the
number of animal individuals that once lived on
Earth were already
extinct, threatening the basis for human existence too.
Future biosphere extinction
See also: Future of
Earth and Fermi paradox
The eventual warming and expanding of the Sun, combined with the
eventual decline of atmospheric carbon dioxide could actually cause an
even greater mass extinction, having the potential to wipe out even
microbes, where rising global temperatures caused by the expanding Sun
will gradually increase the rate of weathering, which in turn removes
more and more carbon dioxide from the atmosphere. When carbon dioxide
levels get too low (perhaps at 50 ppm), all plant life will die out,
although simpler plants like grasses and mosses can survive much
longer, until CO2 levels drop to 10 ppm.
With all photosynthetic organisms gone, atmospheric oxygen can no
longer be replenished, and is eventually removed by chemical reactions
in the atmosphere, perhaps from volcanic eruptions. Eventually the
loss of oxygen will cause all remaining aerobic life to die out via
asphyxiation, leaving behind only simple anaerobic prokaryotes. When
the Sun becomes 10% brighter in about a billion years,
suffer a moist greenhouse effect resulting in its oceans boiling away,
while the Earth's liquid outer core cools due to the inner core's
expansion and causes the
Earth's magnetic field
Earth's magnetic field to shut down. In the
absence of a magnetic field, charged particles from the Sun will
deplete the atmosphere and further increase the Earth's temperature to
an average of ~420 K (147 °C, 296 °F) in 2.8 billion
years, causing the last remaining life on
Earth to die out. This is
the most extreme instance of a climate-caused extinction event. Since
this will only happen late in the Sun's life, such will cause the
final mass extinction in Earth's history (albeit a very long
Effects and recovery
The impact of mass extinction events varied widely. After a major
extinction event, usually only weedy species survive due to their
ability to live in diverse habitats. Later, species diversify and
occupy empty niches. Generally, biodiversity recovers 5 to 10 million
years after the extinction event. In the most severe mass extinctions
it may take 15 to 30 million years.
The worst event, the Permian–
Triassic extinction, devastated life on
earth, killing over 90% of species.
Life seemed to recover quickly
after the P-T extinction, but this was mostly in the form of disaster
taxa, such as the hardy Lystrosaurus. The most recent research
indicates that the specialized animals that formed complex ecosystems,
with high biodiversity, complex food webs and a variety of niches,
took much longer to recover. It is thought that this long recovery was
due to successive waves of extinction which inhibited recovery, as
well as prolonged environmental stress which continued into the Early
Triassic. Recent research indicates that recovery did not begin until
the start of the mid-Triassic, 4M to 6M years after the
extinction; and some writers estimate that the recovery was not
complete until 30M years after the P-T extinction, i.e. in the late
Triassic. Subsequent to the P-T extinction, there was an increase
in provincialization, with species occupying smaller ranges –
perhaps removing incumbents from niches and setting the stage for an
The effects of mass extinctions on plants are somewhat harder to
quantify, given the biases inherent in the plant fossil record. Some
mass extinctions (such as the end-Permian) were equally catastrophic
for plants, whereas others, such as the end-Devonian, did not affect
Geologic time scale
Global catastrophic risk
List of impact craters on Earth
List of largest volcanic eruptions
List of unconfirmed impact craters on Earth
The Sixth Extinction: An Unnatural History (nonfiction book)
Timeline of extinctions in the Holocene
Dissolved oxygen became more widespread and penetrated to greater
depths; the development of life on land reduced the run-off of
nutrients and hence the risk of eutrophication and anoxic events; and
marine ecosystems became more diversified so that food chains were
less likely to be disrupted.
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