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Mass Extinctions
The struggle for life on earth
Mass Extinction - Definition• A significant proportion of
species become extinct (between 30% and 95%)
• The extinctions operate across a wide range of
environments and lifestyles
• The extinctions occurred rapidly (over a few million
years) and were due to one or more physical
factors
The “Big Five” Mass Extinctions identified since the Cambrian Extinction Event Date of Extinction
End of Ordovician 443 Million years ago
Late Devonian 375 Million years ago
End of Permian 251 Million years ago
End of Triassic 200 Million years ago
End of Cretaceous 65 Million years ago
The 5 Major Mass Extinctions
Gaps between extinctions vary from 51 Ma to 135 Ma with an average gap of 94.5
Ma
Percentage of Species Wiped Out
• Ordovician-Silurian - 85%• Late Devonian - 82%• Permian-Triassic - 96%• End Triassic - 76%• Cretaceous-Tertiary - 76%
Extinctions During the Phanerozoic
The Phanerozoic is from 542 Ma (Cambrian) to the present
End of Ordovician Mass Extinction – 443 Ma
70% of marine species became extinctTropical faunas badly affected especially coral reefs
Main groups affected Trilobites, Graptolites, Echinoids, Brachiopods
Late Devonian Mass Extinction – 375 Ma A series of events that lasted around 10 Ma
Cephalopods, Fish and Corals most affected
End Permian Mass Extinction – 251 Ma
The largest mass extinction event removing 95% of marine species and 50% of marine families
Trilobites, Cephalopods, Bryozoans, Corals, Crinoids badly affected
Major faunal and floral overturn on land Marks the boundary between dominance
by the Palaeozoic and Modern Fauna
Permian Mass Extinction
100% trilobites
100% blastoids
100% eurypterids
98% crinoids
97% ammonites
100% acanthodians
97% foraminifera
99% radiolaria
96% brachiopods
End Triassic Mass Extinction – 200 Ma Multiple event mostly affected the land
where over 95% floral species eliminated
Around 30% marine species became extinct – mainly reef dwellers, Ceratites, Brachiopods and Bivalves
End Cretaceous Mass Extinction – 65 Ma
Around 70% of all species wiped outDinosaurs, Reptiles, Ammonites, Belemnites,
Brachiopods, Bivalves, Foraminifera
End-Cretaceous Mass Extinction
100% belemnites
100% dinosaurs
100% mosasaurs
100% ammonites
90% foraminifera
few radiolaria
100% pterosaurs
100% ichthyosaurs
few plants
Dinosaur extinction theories
Causes of Mass Extinctions Supercontinent FormationExtra-Terrestrial ImpactsFlood Basalt Eruptions
Methane Hydrates and Global WarmingRapid and Major Glaciation Events
Supercontinent Formation Pangea formed at the
end of the Permian
Resulted in fewer continental shelves and lack of habitat for
shallow marine organisms
Coincided with huge decline in the numbers of shallow
marine species
Caused rapid fluctuations in climate, unstable weather
patterns and extreme aridity in the interior of the land mass
Supercontinent Formation A single continent reduces the
input of nutrients to oceans from rivers and estuaries
This decreases the amount of nutrients available for shallow
water marine life and may have also altered the salinity
Supercontinent Formation A supercontinent positioned close to one of the poles can
initiate major glaciations
Glaciation causes sea levels to fall and there is a significant
reduction in shallow water marine environments
A supercontinent located over a pole can also lead to the coverage
of the Earth in ice, a condition known as ‘Snowball Earth’
Extra-Terrestrial Impacts Asteroids 1 km diameter strike the Earth every 500,000 years
Large collisions with 5 km diameter asteroids occur approximately about
once every 10 million years The last known impact of an object of 10km diameter or larger was 65Ma
Extra-Terrestrial Impacts
Local destruction of habitats – impact blast, shockwave, ignition of wildfires
Billions of tonnes of debris injected into the atmosphere resulting in rapid global
cooling
Extra-Terrestrial Impacts
Impact in the sea – billions of tonnes of water vapour
injected into the atmosphere resulting in a greenhouse effect and rapid
global warming
Flood Basalt Eruptions
Eruptions last between 0.5 and 2.0 million years and can erupt enough basalt to cover the whole of the USA to a
depth of a kilometreLocal destruction of habitats
and initiation of wildfires
Flood Basalt Eruptions
Billions of tonnes of carbon dioxide and
sulphur dioxide released into the atmosphere
during eruptions
Both are powerful greenhouse gases and will contribute to very rapid global warming
Flood Basalt Eruptions
When it rains the sulphur dioxide will come back down to Earth dissolved in rainwater and
the acid rain will kill vegetation on a large scale
With vegetation dying, all food chains will be affected and also the oceans may become acidified with disastrous effects on marine life
Siberian volcanism in the Permian period
78 84 90 96 102 108 114 120
48
52
56
60
64
68
UK atsame scale
SiberianTraps
WestSiberian
Basin
00
SiberianTraps
WestSiberian
Basin
Methane Hydrates in Ocean Floor Sediments Large volumes currently locked into ocean floor sediments
Stable under low temperatures of deep ocean
What is methane hydrate?
Methane molecule (CH4)
in a 'cage' of H2O molecules
Structure held together by hydrogen bonds
"The ice that burns"
Methane Hydrates in Ocean Floor Sediments
Global warming may result in deep ocean
temperatures rising and the release of large volumes of
methane from ocean sediments
The rapid release of large amounts of methane into the atmosphere will result
in highly accelerated global warming
Methane Hydrates in Permafrost
Glaciations-Possible Causes
Supercontinents positioned in high latitudes/close to the poles
Milankovitch cycles: Precession, Obliquity and Eccentricity
Glaciations-Effects on Ecosystems
Loss of habitat as ice masses growCould eventually lead to ‘Snowball Earth’ scenarioContraction of climatic belts towards the equator
Global cooling, decreased productivity of primary producers
End Cretaceous Mass Extinction – 65 Ma
A large bolide (asteroid or meteorite 10km in diameter) collided with the Earth 65 million years
ago
K-T extinction
And then what?
• Fireball• Tsunami• Wildfires• Dust and darkness• Acid rain• Increased CO2 and global warming
Evidence - Asteroid Impact Location
Location of possible impact site discovered on the Yucatan Peninsula in Mexico at Chicxulub
The impact structure is a circular depression about 180 km in diameter
Evidence for Asteroid Impact Location
A. Gravity survey onshore and offshore of the Yucatan PeninsulaB. 3D map of gravity and magnetic field variations reveals the
Chicxulub crater, now buried beneath tons of sediment. This view is looking down at the surface, from an angle of about 60°.
A
B
Evidence – The K-T Boundary LayerThe presence of a thin 2cm
layer of iridium-rich clay found all over the world
within sedimentary rocks
The K-T Boundary Layer dates the same everywhere
at 65.5 Ma +/- 0.3 Ma
Iridium is a transition element, rare on Earth but
found in meteorites.
First proposed by Luis Alvarez in 1980
Evidence – Shocked Quartz
Shocked quartz is found worldwide, in a thin layer
at the boundary between Cretaceous and Tertiary rocks.
It was first discovered at nuclear testing sites and later in craters caused by meteorite impacts as
at the Barringer Crater near Flagstaff, Arizona in the USA
Evidence – Shocked QuartzShocked quartz has a microscopic structure
different from normal quartz.
Under intense pressure, but relatively low temperature,
the crystalline structure of quartz is deformed along planes inside the crystal.
These planes, which show up as lines under a
microscope, are called planar deformation features
(PDFs), or shock lamellae.
Evidence – Tektites (Glass Spherules)Tektites (from Greek
tektos, molten) are natural glass rocks up to a few
centimetres in size.
Most scientists agree they are formed by the impact
of large meteorites on Earth’s surface.
Tektites are black or olive-green in colour and their
shape varies from rounded to quite irregular.
Tektites (Glass Spherules) from 1 to 8 mm in diameter are found within a radius of 600 to 1,000km of the Chixulub Crater in Mexico
Evidence – Soot from Wildfires
The K-T Layer has high concentrations of carbon in many locations,suggesting that the asteroid impact may have generated wildfires.
Large areas of vegetation would have been destroyed in a short time,soot fell to Earth and was incorporated into sedimentary rocks
Evidence – Tsunami DepositsIt is thought that the asteroid
impact occurred in the sea and initially produced a crater 100
km wide and 30 km deep
This would have displaced vast volumes of seawater and
generated a series of very large tsunamis possibly over
100 metres in height
The tsunamis would have travelled great distances inland, and in Texas at Waco there are
large-scale sedimentary deposits thought to be of tsunami origin.
Evidence – Tsunami DepositsThe tsunami deposits in Waco, Texas are thought to be from
the waves generated by the K-T asteroid impact.
The sediments are estimated to have been deposited at least
300km inland by the tsunamis!
Animation to show Impact of a large asteroid with the Earth
The impactor's estimated size was about 10 km in diameter and is estimated to have released 4×1023 joules of energy,
equivalent to 100,000,000 megatons of TNT on impact.
Never mind the bolides……Flood Basalt Eruptions 66 Ma – The Deccan Traps
Erupted mainly over a period of 30,000 years Over 2000 metres thick and cover 500,000 km²
May have originally covered 1,500,000 km²Caused a global drop in temperature of 2°C
The term Trap is derived from the Dutch for stairs and refers to the step-like landscape of the area
The Sixth Mass Extinction?
Today
http://en.wikipedia.org/wiki/Geologic_time_scale
• Following their evolution humans have caused huge species loss, and this has accelerated in since the 19th century •Species are becoming extinct at a rate of about 4000/year, 100/day, 1 species every 15 minutes.
NASA
•Are we now in the midst of a sixth mass extinction?
Meanwhile….the K-T debate continues…
• 31 August 2002 “Cold was killing dinosaurs long before the asteroid commonly thought to have been their downfall hit, according to scientists.”
• 11 June 2002 “Dino heatwave recorded in leaves” … “analysis of fossil leaves from 65 million years ago shows there was a sudden and dramatic rise in carbon dioxide in the Earth's atmosphere. “
… and the P-Tr debate rumbles on…
• 6 June 2002 “A huge outpouring of molten rock 250 million years ago may have been the decisive factor in the deaths of nearly all lifeforms on the Earth at that time.”
• 23 February 2001 “Earth's biggest mass extinction 251 million years ago was triggered by a collision with a comet or asteroid, US scientists say.”
http://www.firstscience.com/SITE/articles/mac_f2.asp
Conclusions
• The largest extinctions of the last 300 m.y. correlate with massive volcanism.
• At least one also correlates with a significant meteorite impact.
• There are far more impact and volcanic events than there are mass extinctions.
• This rules out simple causal relationships between volcanism and extinctions, or impact and extinctions.
• The “Murder on the Orient Express” hypothesis shows that combinations of driving factors are probably more important.
• These complications lead to conflicting reports in the media
That’s All Folks!