Transcript K–T extinction event

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 coevolutionary 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
Table T01: Details of the Five Major Mass
Extinction Events Since the Cambrian
Source: Raup, D.M. and J.J. Sepkoski, Jr., Science 231 (1986):
833–835.
The Fossil Record – Key to the Past
An Incomplete Record
 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.
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 End Ordovician Mass Extinction
 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 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 Late Devonian Mass Extinction
 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 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 End Permian Mass Extinction
 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 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 End Triassic Mass Extinction
 The fourth of the five mass extinctions.
 Happened about 210 million years ago.
 Impacts on life forms:

Plants: several orders of gymnosperms were lost and the Umkomasiales (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 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 End Cretaceous Mass Extinction
 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 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 activity
Impact 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 Future?
 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 Present Mass Extinction – Phase Two
 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
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)

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