1. Mass Extinctions
I.G. Kenyon

2. 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

3. 5 Major 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

4. The 5 Major Mass Extinctions
Gaps between extinctions vary from 51 Ma
to 135 Ma with an average gap of 94.5 Ma

5. Extinctions During the Phanerozoic
The Phanerozoic is from 542 Ma (Cambrian) to the present

6. Diversity Curves through the Phanerozoic
End Triassic Mass Extinction
possibly caused by submarine
volcanism associated with the
break up of Pangea

7. End of Ordovician Mass Extinction – 443 Ma
70% of marine species became extinct
Tropical faunas badly affected especially coral reefs
Main groups affected Trilobites,
Graptolites, Echinoids, Brachiopods

8. Late Devonian Mass Extinction – 375 Ma
A series of events that lasted around 10 Ma
Cephalopods, Fish and Corals most affected

9. 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

10. 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

11. End Cretaceous Mass Extinction – 65 Ma
Around 70% of all species wiped out
Dinosaurs, Reptiles, Ammonites, Belemnites,
Brachiopods, Bivalves, Foraminifera

12. Causes of Mass Extinctions
Supercontinent Formation
Extra-Terrestrial Impacts
Flood Basalt Eruptions
Methane Hydrates and Global Warming
Rapid and Major Glaciation Events

13. 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

14. 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

15. 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’

16. 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

17. 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

18. 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

19. 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 kilometre
Local destruction of habitats
and initiation of wildfires

20. 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

21. 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

22. Methane Hydrates in Ocean Floor Sediments
Large volumes currently locked into ocean floor sediments
Stable under low temperatures of deep ocean

23. 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

24. Methane Hydrates in Permafrost

25. Glaciations-Possible Causes
Supercontinents positioned
in high latitudes/close to the poles
Milankovitch cycles: Precession,
Obliquity and Eccentricity

26. Glaciations-Effects on Ecosystems
Loss of habitat as ice masses grow
Could eventually lead to ‘Snowball Earth’ scenario
Contraction of climatic belts towards the equator
Global cooling, decreased productivity of primary producers

27. End Cretaceous Mass Extinction – 65 Ma
A large asteroid or meteorite (10km in diameter)
collided with the Earth 65 million years ago

28. Evidence - Asteroid Impact Location
Location of possible impact site discovered on
the Yucatan Peninsula in Mexico at Chixulub
The impact structure is a circular
depression about 180 km in diameter

29. Evidence for Asteroid Impact Location
A
B
A. Gravity survey onshore and offshore of the Yucatan Peninsula
B. 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°.

30. Evidence – The K-T Boundary Layer
The 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

31. 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

32. Evidence – Shocked Quartz
Shocked 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.

33. 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 (Glass Spherules)
from 1 to 8 mm in diameter
Tektites are black or olive-
are found within a radius
green in colour and their
of 600 to 1,000km of the
shape varies from rounded
Chixulub Crater in Mexico
to quite irregular.

34. 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

35. Evidence – Tsunami Deposits
It 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.

36. Evidence – Tsunami Deposits
The 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!

37. 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.

38. Origin of the K-T Asteroid
Results published in 2007 suggest that the impactor that
wiped out the dinosaurs and other life forms on Earth 65
million years ago can been traced back to a break-up event
in the main asteroid belt more than 100 million years earlier.

39. 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 km²
Caused 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

40. That’s All Folks!