Extinction

Overview• Extinctions are as important in the history of life as are the

evolution of new species• Explaining extinctions is just as challenging a scientific

question as explaining the evolution of new species• Extinctions are opportunities for adaptive radiations

because extinctions open or re-open niches for new species to invade and occupy

• To understand extinctions, we need to identify rates, patterns and causes

Extinctions

•We know very little about natural extinctions, especially the precise causes

•Fossil records demonstrate that extinctions have occurred repeatedly in the past

•But physical evidence of causative agents are rarely preserved

•Cause and Effect is hard to establish

Extinctions• Habitat Disruption

• Volcanic Eruptions• Asteroid Impacts• Sea Level Change

• Habitat Modification• Climate Change• Mountain-Building• Sea Level Change• Precipitation Change• Toxic Materials

• “Exotic” Species Introductions• Continental Drift

Co-Evolution & Niches• Any species living in a niche has evolutionary

relationships with other species; some casual, some crucial

• Therefore, the extinction of a species will have repercussions in the niches of all species which have co-evolutionary relationships with the newly extinct species

Rates of Extinction• There is much debate about the degree and the importance of

different rates of extinction

• Once again, the incomplete fossil record makes answering the question far more difficult

• The simple comparison is between a background rate of “uniform” extinctions, and the occasional episodes of “mass” extinctions

Rates of Extinction• There is much debate about the degree and the importance of

different rates of extinction

• Once again, the incomplete fossil record makes answering the question far more difficult

• The simple comparison is between a background rate of “uniform” extinctions, and the occasional episodes of “mass” extinctions

Source: Raup, D.M. and J.J. Sepkoski, Jr., Science 231 (1986): 833–835.

Table T01: Details of the Five Major Mass Extinction Events Since the Cambrian

The fossil record is known to be incomplete. Some time periods are poorly represented

by sedimentary rock formations. Lazarus taxa Many large extinct species are poorly represented. The rate of description of new fossil species is steady.

Fossil formation depends on the durability of the specimen, burial and lack of oxygen. Most organisms do not form fossils because: They do not have hard skeletal parts, They get eaten, They occur where decay is rapid or deposition does not occur, They did not live/die during a period of sedimentation.

The Fossil Record – Key to the Past

An Incomplete Record

Potential Triggers• Asteroid Impacts = sudden

Gradual: Large Basalt Outflows

• Large CO2 changes which can affect atmospheric and ocean chemistry (slow)

At least a dozen significant events

The concept of impact induced extinction events is relatively new – first evidence came in 1980 regarding the KT event (65 million years ago – dead dinosaurs).

Further research and data have now shown that such events are common.

Five Agreed Upon Major Events

Periodic (?) Extinctions of Varying Amplitude (percent extincted)

Relatively stable

The earliest of the five mass extinctions. Happened about 439 million years ago. Impacts on life forms:

Plants, insects and tetrapods had not yet developed so they were not affected.

Marine organisms affected: brachiopods, cephalopods, echinoderms, graptolites, solitary corals and trilobites.

Suggested causes include: Climate change, A drop in sea level, Asteroid or comet impacts, A gamma ray burst.

The End Ordovician Mass Extinction

The Ordovician Extinction Event• At the time, all known metazoan life was confined to the

seas and oceans• More than 60% of marine invertebrates died; brachiopods,

bivalves, echinoderms, bryozoans and corals were particularly affected

• The immediate cause of extinction appears to have been the tectonic movement of Gondwana into the south polar region

Middle Ordovician

The second of the five mass extinctions. Happened about 365 million years ago. Impacts on life forms:

Insects and tetrapods had not yet developed so they were not affected.

Plants: the rhyniophytes decreased. Marine organisms affected: ammonoids, brachiopods, corals,

agnathan fish, placoderm fish, ostracods and trilobites.

Suggested causes include: Climate change, Multiple asteroid impacts.

The Late Devonian Mass Extinction

The Devonian Extinction Event

• The causes of the Devonian extinctions are unclear• The extinction of ~20% of all animal families and 70-80% of all animal species

• Leading theories include changes in sea level and ocean anoxia, possibly triggered by global cooling (glaciation on Gondwana) or oceanic volcanism

• The widespread oceanic anoxia prohibited decay and allowed the preservation of sedimented organic matter as petroleum

• The impact of a comet or another extraterrestrial body has also been suggested, but the evidence is weak

Late Devonian / Early Carboniferous

The third and biggest of the five mass extinctions happened about 245 million years ago.

Impacts on life forms: Plants: the previously dominant Ottokariales (glossopterids)

became extinct. Insects: about two thirds of the insect families became extinct

and six insect orders disappeared. Tetrapods affected: amphibians and mammal-like reptiles Marine organisms affected: benthic foraminifera, brachiopods,

bryozoans, echinoderms, 44% of fish families, all graptolites, solitary corals and all trilobites.

Suggested causes include: climate change, a drop in sea level, massive carbon dioxide (CO2) poisoning, oceanic anoxia, the explosion of a supernova, asteroid or comet impacts, plate tectonics during the formation of Pangea and high volcanic activity.

The End Permian Mass Extinction

The Permian Extinction Event• The Earth's most severe mass extinction event, with up to

96% of all marine species and 70% of terrestrial vertebrate species becoming extinct

• It is the only known mass extinction of insects• Some 57% of all families and 83% of all genera were

killed• Because so much biodiversity was lost, the recovery of

life on Earth took significantly longer than after other extinction events

The Permian Extinction Event• There were from one to three distinct pulses of extinctions

that occurred about 245-251 million years ago• There are several proposed mechanisms for the

extinctions• The earlier phase was likely due to gradual environmental

change, while the latter phase may has been due to a catastrophic event

The Permian Extinction Event• Suggested mechanisms for the latter catastrophic

extinction pulse include: • large or multiple bolide (meteor/comet) impact events• increased volcanism and sudden release of methane clathrate from

the sea floor• gradual changes include sea-level change, anoxia, increasing

aridity, and a shift in ocean circulation patterns driven by climate change

• Excess dissolved CO2 acidified the oceans, contributing to the decline of shelled organisms

Late Permian

The fourth of the five mass extinctions. Happened about 210 million years ago. Impacts on life forms:

Plants: several orders of gymno-sperms were lost and the Umkoma-siales (Dicroidium) became extinct.

Insects: not severely affected. Tetrapods affected: some reptile lineages – the mammal-like

reptiles (therapsids) especially. Marine organisms affected: ammonites, ammonoids, bivalves

(Molluscs), brachiopods, corals, gastropods and sponges. Suggested causes include: one or more asteroid/comet impacts,

climate change and volcanic activity.

The End Triassic Mass Extinction

The Triassic Extinction Event• The first of the final two more modest

of the five major extinction events• The extinction occurred around 208

million years ago and happened in less than 10,000 years just before Pangaea started to break apart

• This extinctions struck marine life and terrestrial life profoundly

• At least half of the species now known to have been living at that time went extinct

• In the seas, a whole class (conodonts) and 20% of all marine families disappeared• Conodonts were early eel-like chordates

The Triassic Extinction Event• Several explanations for this event have been suggested, but all have unanswered challenges:• Gradual climate change or sea-level fluctuations during the

late Triassic; however, this does not explain the suddenness of the extinctions in the marine realm

• Asteroid impact, but no impact crater has been dated to coincide with the Triassic–Jurassic boundary; the largest late Triassic impact crater occurred about 12 million years before the extinction event

• Massive volcanic eruptions (known from the central Atlantic magmatic province -- an event that triggered the opening of the Atlantic Ocean) that the would release CO2 or sulfur dioxide and aerosols, which would cause either intense global warming (from the former) or cooling (from the latter)

The final and best known of the five mass extinctions.

Happened about 65 million years ago. Impacts on life forms:

Plants: debatably up to 75% of species. Insects: not severely affected. Tetrapods affected: 36 families from 3 groups (dinosaurs (all

non-avian), plesiosaurs and pterosaurs. Marine organisms affected: ammonites, ammonoids,

cephalopods, bivalves, foraminifera, icthyosaurs, mosasaurs, plackton and rudists.

Suggested causes include: asteroid/comet impact, climate change and volcanic activity.

The occurrence of an impact event has been verified.

The End Cretaceous Mass Extinction

The Late Cretaceous Extinction Event• The second of two more modest extinction events, the fifth

and final of the five major extinction events• There is agreement that it was a relatively rapid extinction

event dated to 65.5 million years• Widely known as the K–T extinction event, it is

associated with a geological signature known as the K–T boundary, usually a thin band of iridium-rich sedimentation found in various parts of the world

The Late Cretaceous Extinction Event• Scientists theorize that the K–T extinctions were caused by one or more catastrophic events, such as massive asteroid impacts

• Like the Chicxulub impact, a 10km diameter meteorite, leaving a crater ~200 Km in diameter

• or increased volcanic activityImpact caused acid rain, ash that blocked out the sun for months, severe global cooling (nuclear winter). Increase in atmospheric CO2, resulting in global warming, the final blow to dinosaurs & many other Cretaceous species.

The Late Cretaceous Extinction Event• These geological events may have reduced sunlight and hindered photosynthesis, leading to a massive disruption in Earth's ecology

• Other researchers believe the extinction was more gradual, resulting from slower changes in sea level or climate

The Late Cretaceous Extinction Event

• Before the end of the Cretaceous, flight evolved independently three times:• Insects, flying reptiles, birds (avian dinosaurs)

• By the end of the Cretaceous 65 Mya, most dinosaurs along with other large marine reptiles and various invertebrates died out

• No land vertebrate larger than a large dog survived the KT boundary event

Late Cretaceous

The Impact of Extinctions

• "The picture's pretty bleak, gentlemen . . . the world's climates are changing, the mammals are taking over, and we all have a brain about the size of a walnut."

The present extinction acts differently to previous mass extinctions. Extinction, excluding as a result of catastrophes, happens in stages. There is insufficient knowledge of the natural world to predict how

much extinction ecosystems can experience without loss of function. If the present extinction event continues unchecked, we could push

ecosystems beyond the threshold at which they can maintain their functions and thus sustain themselves and us. This would result in the demise of Homo sapiens.

Biodiversity has recovered following each mass extinction but only after the cause of the event had dissipated.

To end the present mass extinction, we must change our present behaviour.

If mass extinctions do occur periodically, then the next natural mass extinction should occur in the next 10 million years.

The Future?

The second phase began with the development of agriculture about 10 000 years ago.

Agriculture allowed humanity to live outside the boundaries of local ecosystems.

We are causing major environmental changes. The drivers for this sixth mass extinction are

agriculture and human overpopulation, overexploitation and invasive species.

This is seemingly the first mass extinction to have a biotic cause. The effects of this mass extinction are hidden by:

The existence in the wild of the remnant populations of several species,

Our Eyes are Closed

The Present Mass Extinction – Phase Two

Recent Extinctions• Auroch (1627) & Dodo (1662)• Stellar’s Sea Cow (1768)• Mascarene Island Giant Tortoise

(1795)• South African Cape Lion (1858)• Quagga (1883) • Passenger Pigeon (1914)• Tasmanian Wolf (1936)• Bali Tiger (1937) / Javan Tiger (1976)• Kaua’i ‘O’o (1987)• Golden Toad (1989)• Baiji White Dolphin (2006)• Chinese Paddlefish (2007)• Christmas Island Pipistrelle (2009)• Vietnamese Rhinoceros (2010)• Pinta Island Tortoise (2012)

By 2050 - 2100? 50% of all species on the planet will be either

endangered or extinct Habitat destruction Global Warming

25% mammalian species 15% bird species In The Future of Life (2002), E.O. Wilson of

Harvard calculated that, if the current rate of human disruption of the biosphere continues, one-half of Earth's higher lifeforms will be extinct by 2100 *we have become GOD