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 ID: 278601
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Slide1
ExtinctionSlide2
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 causesSlide3
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 establishSlide4
Extinctions
Habitat Disruption
Volcanic Eruptions
Asteroid Impacts
Sea Level Change
Habitat Modification
Climate Change
Mountain-BuildingSea Level ChangePrecipitation ChangeToxic Materials“Exotic” Species IntroductionsContinental DriftSlide5
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 speciesSlide6
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” extinctionsSlide7
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” extinctionsSlide8
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 CambrianSlide9
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 RecordSlide10
Potential Triggers
Asteroid Impacts = suddenSlide11
Gradual: Large Basalt Outflows
Large CO
2
changes which can affect atmospheric and ocean chemistry (slow)Slide12
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
.Slide13
Five Agreed Upon Major EventsSlide14
Periodic (?) Extinctions of Varying Amplitude (percent
extincted
)
Relatively stableSlide15
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 ExtinctionSlide16
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 regionSlide17
Middle OrdovicianSlide18
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 ExtinctionSlide19
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 petroleumThe impact of a comet or another extraterrestrial body has also been suggested, but the evidence is weakSlide20
Late Devonian / Early Carboniferous Slide21
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 ExtinctionSlide22
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 eventsSlide23
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 eventSlide24
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 organismsSlide25
Late PermianSlide26
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 ExtinctionSlide27
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 disappearedConodonts were early eel-like chordatesSlide28
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 CO
2
or sulfur dioxide and aerosols, which would cause either intense global warming (from the former) or cooling (from the latter)Slide29
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 ExtinctionSlide30
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 worldSlide31
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 activity
Impact caused acid rain, ash that blocked out the sun for months, severe global cooling (nuclear winter).
Increase in atmospheric CO
2
,
resulting in global warming, the final blow to dinosaurs & many other Cretaceous species.Slide32
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 climateSlide33
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 eventSlide34
Late CretaceousSlide35
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." Slide36
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?Slide37
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 TwoSlide38
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)Slide39
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