Download 7. Extinctions

Lecture 6: Extinctions a global environmental process
1. Major extinctions
2. Theories of episodicity
3. Focus on the K-T
4. Implications for global diversity
Sepkoski’s Curves
An analysis of shallow marine
diversity through time
Family diversity
Ord
Dev
P Tr
Cambrian fauna
Ordovician radiation
End Permian extinction
Diversity = evolution - extinction
Cret
Mass extinction
End Ordovician
Biological expression
About 70% of marine species became
extinct. Tropical faunas in general were
badly damaged, especially reefs. Main
affected groups were trilobites,
graptolites, echinoderms and
brachiopods.
Probable causes
A sudden, major glaciation, spreading from
the South Pole. Most of the tropical belt
disappeared. Sea levels fell, reducing the
shallow shelf area, and cold water faunas
moved to low latitudes, excluding warmer
water ecosystems.
End Devonian
A series of events lasting about 10 My.
This extinction was characterised by low
rates of origination and extinction rates
as such remained unexceptional.
Cephalopods, fish, corals most affected.
The least understood mass extinction. Seabed
anoxia or extraterrestrial impact have been
cited. Another suggestion is that the marine
ecosystem was badly affected by the rise of
land plants and a short-lived drawdown of
CO 2.
End Permian
The largest mass extinction, removing
95% of marine species and over 50% of
marine families. Trilobites, cephalopods,
corals, bryozoans and crinoids badly
affected. Major faunal and floral
overturn on land. Marks the boundary
between dominance by the Palaeozoic
and Modern fauna.
Event may relate in some way to the
supercontinent of Pangea, which would have
affected world climates and oceanic
conditions. The largest terrestrial igneous
province was emplaced in Siberia at this time,
and would have changed climate over a range
of timescales. There is controversial evidence
for meteorite impacts at this boundary.
End Triassic
A multiple event again. Most
important on land, where floral
overturn exceeded 95%. Around 30%
of marine species became extinct,
mainly reef dwellers including ceratite
ammonites, brachiopods and bivalves.
Recent work suggests that widespread
submarine volcanic activity may have been
responsible for massively elevated CO2 levels
at this time. This volcanic activity was a
function of the break-up of Pangea.
End Cretaceous
Dinosaurs, marine and aerial reptiles,
ammonites, belemnites became extinct.
Brachiopods, bivalves and foraminifera
severely affected.
Most commonly attributed to a major
meteorite impact into the Yucatan area of
Mexico. Underlying sulphates and
limestones would have vapourised to produce
acid rain. Short term cooling (from dust and
sulphur dioxide) and long term warming from
carbon dioxide) resulted. Also linked to the
Deccan Igneous province in India.
The K-T Boundary
65 Ma ago
65% extinction
Oceans Survival Guide
Near surface
High latitude
Simple skeleton, not limy
Small size, cysts
Land Survival Guide
Small size
Ferns
Detritus feeder
Iridium spike
Microtektites
Shocked quartz
Plate tectonics
Deccan Traps
A Large Igneous
Province (LIP)
Mantle structure
Mantle
heterogeneity
Mantle Plumes
Possible cooling effects
Deccan effects
Eruptions reached troposphere
Gases - carbon dioxide,
sulphur dioxide,
hydrogen chloride
Ash
Atmosphere cools then heats,
perhaps by 100 C
Ozone destroyed
Eruptions from fissures
400 km long
Terrestrial eruptions maximum effect on
atmosphere
Oceans become acidic
Extinction correlation
6. End Cretaceous event
30% families extinct
65% species extinct
Dinosaurs, marine and flying reptiles,
ammonites extinct.
Two likely causes a. Meteorite impact
b. Deccan Trap volcanism
Iridium
spike
Shocked
quartz
Microtektites
Cretaceous
Palaeogene
Yucatan
impact
crater
Crust
Mantle
plumes
D’’ layer
Core
Deccan
traps
Sepkoski’s Curves
An analysis of shallow marine
diversity through time
Family diversity
Ord
Dev
P Tr
Cambrian fauna
Ordovician radiation
End Permian extinction
Diversity = evolution - extinction
Cret