03/10/2016
In this lecture:
Geology and Life
Timescales
• The Earth is about 4.5 billion years old.
• Life has been around for about 3.9 billion
years.
• Understanding and dating major changes in
the history of Earth and it’s life is key to
piecing together evolutionary history.
• Geological timescales
• Geological drivers of diversity
• Extinction
Geological time
• Rocks grouped together based on changes in
fossils.
• Major changes in biotas mark greater events.
• Eon > Era > Period > Epoch
• Many subdivisions.
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Geological Drivers of Evolution
Trends in Biodiversity
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Changes
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Evolution cannot predict the future.
The Earth is constantly changing.
This will lead to change.
(Species will also change in response to each
other).
Plates
Tectonic movement
Vulcanism
Climate change
Bolides
Moving Continents
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Evidence from palaeontology
Effects?
• How might moving plates and continents
change environments and conditions?
Leads to
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Changing coastlines.
Changing continental mass.
Changing currents.
Changing climate and weather.
Altered access to locations (join and cut off).
Vulcanism
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Speed
• Changes can be rapid, e.g. 2004 Sumatra
earthquake:
• Propagation along the fault was 2 km/s.
• Led to a move of over 20 m in seconds.
• Some islands double in size as uplifted.
Climate change
Local effects on climate (e.g. hot springs).
Local resources (fertile soils, black smokers).
Island formation (and destruction).
Global effect on climate.
• Climate change is normal.
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Interactions
Bolides
• Extra terrestrial origins for most of Earth’s
water.
• Major impacts have huge local, and even
global, effects.
Bolide impact
Climate change
Vulcanism
Tectonic movement
• Mass extinctions
• Adaptive radiations
• Large scale migrations
• Speciation
Extinctions
• Extinction is normal (though not the current
rate).
• Can be individual populations or species, local
or major events.
• There have been 5 mass extinctions.
Big 5
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End Ordovician - 444 mya
End Devonian – 375 mya
End Permian (Permian-Triassic) – 251 mya
End Triassic – 200 mya
End Cretaceous (Cretaceous-Tertiary or KT) –
65 mya
Ordovician Extinction
• Primarily affected marine communities.
• Many invertebrate groups suffered e.g.
bryozoans, trilobites, corals, echinoderms.
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Why?
• Unclear but major increase in ice levels (and
accompanying sea level drop).
• Possibly initiated by ash from vulcanism.
Why?
• Several pulses of extinction close together
rather than one big one.
• Widespread anoxia.
• Rapid sea level changes.
• Cause unknown but may be triggered by
terrestrial plants.
Why?
• Possible bolide impact or increase in
vulcanism.
• Huge methane release changing climate.
• Drop in oxygen and increase in carbon dioxide.
• Rapid change in climate, atmosphere and
ocean acidity.
Devonian
• Only affected aquatic systems.
• Losses in stromatolites and corals.
• Drops in trilobites, ammonites, graptolites,
and conodonts.
Permian
• Huge loss of many species
(esp marine).
• Extinction of the
trilobites, loss of many
ammonites, brachiopods
and crinoids.
• Loss of many insect
groups.
Triassic
• Non-dinosaur archosaurs, therapsids, large
amphibians.
• Ammonites and conodonts.
• Plants largely unaffected.
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Why?
• Unclear but possibly volcanically triggered
eruption of greenhouse gases (esp carbon
dioxide).
• Breakup of Pangea?
• Methane release from ice melt?
• Rapid temperature change.
KT Extinction
• Loss of (non-avian) dinosaurs.
• Numerous other major reptile groups.
• Also birds, mammals, and various
invertebrates.
• Ammonites.
Why?
• Bolide impact.
• Immediate local devastation.
• Nuclear winter.
• Possible involvement of Deccan traps.
And ongoing…
• Species are going extinct at an enormous rate.
• This is comparable to other mass extinctions
given the limited timeframe.
• Early humans hunted many species to
extinction.
• More recent extinctions have been caused by
a variety of human mediated factors.
Human actions
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Invasive species (deliberate and accidental)
Overhunting
Overfishing
Fragmentation of populations
Destruction and disturbance of habitats
Creation of monocultures
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03/10/2016
Climate change
• Human driven climate change threatens entire
ecosystems.
• Record low ice levels, bleaching of coral reefs,
shifts in currents, heatwaves and droughts,
more extreme weather.
• All very rapid.
• This puts huge pressure on species. Many
have been lost, many more are already
doomed.
Conclusions
Further Reading
• The history of the earth is divided into
geological time periods.
• These are defined by characteristic flora and
fauna.
• Large-scale changes in biodiversity (mass
extinctions) were triggered by climate change.
• https://cosmosmagazine.com/palaeontology/
big-five-extinctions
• http://mygeologypage.ucdavis.edu/cowen/~G
EL107/PTect.html
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