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Pg. 66
EXTINCTIONS
Natural Disasters of epic proportions
5 mass extinctions on Earth - know geologic periods and
ages of these events
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1)Ordovician
about 458 million years ago
a.) marine life on sea floor and near surface.
Reef builders hit hard, few reefs survive
into Silurian time.
*Why ? glaciation at that time = cool temperatures
A good link explaining more
ADD Gondwana (large landmass) was near the south pole
at that time. Plate tectonics
????More or less glaciers?
????Sea level change results?
Reef builder and warm water species most profoundly
effected WHY?
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2) Devonian
About 375 million years ago
A good link explaining cause
Fauna included similar to Ordovician and fishes.
a) marine life hit hard but land plants not affected
b) Reefs had a hey-day in the Devonian but were
decimated again in LATE Devonian.
Reefs small for over 200 million years.
*Why? crisis not sudden - took millions of years and is
attributed to global cooling.
Similar to Ordovician- Plate Tectonics
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3)Permian
260 million years ago
Good link with explanation
a.) greatest mass extinction of life on earth.
75-90% of all marine species expired!
b) Terrestrial vertebrates hit hard!
c) Plants seem to be immune - this may be related to
reproductive strategies (only need a small part
to survive – cuttings, seeds)
ADD
A number of things probably contributed-timing
1.) Slow event - occurring over millions of years
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3)Permian CONTINUED ADD
A number of things probably contributed-timing
2.) Pangaea formed and changed…
a.) the amount of warm shallow oceans-DECREASED
b.) large climate CONTRAST-interior of the
continent was way hot/dry and opposite near shore
similar to Australia but even more so.
c.) more competition
3.) Sea-Level fall
a.) spreading at mid-ocean ridge slowed-less volume
in the ocean
b.) this caused the volume of ocean basins to be
decreased=shoreline moving seaward
c.) how effect #2???
ND pg. 438 fig. 15.16
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3)Permian CONTINUED ADD
A number of things probably contributed-timing
4.) Siberian Traps (warm the climate or did it?)
a.) massive amount of flood basalts
b.) possible COUP DE GRACE?
c.) huge release of CO2 and other Greenhouse
gasses
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4) Triassic
About 240 million years ago
a) Amphibians and mammal-like reptiles suffered
great losses.
b) 20% of marine invertebrates families (groups)
gone.
ADD
Causes: all have problems explaining
1.) gradual climatic/sea level change theory?-then
why abrupt extinction?
2.) impact?-no impact crater found
3.) Break up of Pangea-Central Atlantic Magmatic
Province (CAMP)-lots of volcanic emissionsGreenhouse effect-not cooling
*Cooling the culprit?
Added new open niches for dinos to fill.
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5) Cretaceous
BEEN HERE
About 65 million years ago
a) All dinosaurs go extinct. Large reptiles living in ocean
gone too.
b) Extinctions affect marine life.
Tropical hit the hardest
c) Heavy loss of low-latitude flora of N. America.
d) fern spike in N. A. = ferns are good invader species
spread over barren surfaces
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5) Cretaceous CONTINUED
BEEN HERE
*Why? - Impact? or Climate?
Impact evidence - crater, iridium, shocked quartz,
tektites, tsunami deposits.
Climate evidence – some say extinctions may be
gradual - not sudden. Significant volcanic eruptions
at this time (Deccan Traps)- could change climate
HOW???
ADD
Which is considered stronger argument? WHY?
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EVIDENCE PATTERNS IN EXTINCTIONS
USED TO DETERMINE CAUSE
EVIDENCE
1) Land and sea affected (sea often more so).
2) Tropical taxa (groups of critters) eliminated/trashed.
3) If taxa had extended range from tropics to
higher lat. they become compressed
(tropical wiped out and others migrate)
4) Shallow ocean shelf affected more than deep ocean.
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EVIDENCE PATTERNS IN EXTINCTIONS –
USED TO DETERMINE CAUSE continued
EVIDENCE
5) In groups like fish - freshwater and marine
marine suffer more extinctions. Marine adapted to
narrower temp. tolerance.
6) Plants appear immune compared to animals.WHY?
7) Some groups experience repeated extinctions
(invertebrates: trilobites, ammonites).
8) Some believe periodicity to extinctions - every 26
million years. (resolution problem).
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POSSIBLE CAUSE
*All come down to climate change*
1) Global cooling - fits with:
a) compression of species
b) tropical go first seem to be very sensitive to
temp changes (reefs demise)
c) shelf water life goes vs. deep ocean WHY?
d) terrestrial life can adapt (more mobile) better
than marine so possibly have higher probability of survival
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POSSIBLE CAUSE-continued
*All come down to climate change*
Cause of global cooling?
1) Glacial Event - timing doesn’t always fit when it was
cold still had critters around.
2) Plate tectonics - changes ocean circulation as cont.
move = cooling
3) Carbon Dioxide shortage?
Devonian - plants explode and use CO2. Could this
cause a cooling? WHY/HOW?
Opposite of global warming?
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POSSIBLE CAUSE-continued
*All come down to climate change*
Cause of global cooling?
4) Volcanic Eruptions - gas in atmosphere block light also cause acid rain which could change ocean
geochemistry maybe cause problems on land also
5) Impact = nuclear winter - break down food chains
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2) Global Warming?
a) modern example
1982-83 El Nino entire species of clam dies - off
coast of SA
Well - OK but that is local how about global?
Warming events don’t match with species compression
pattern
ANY COMMENTS???
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3) Habitat Loss Changing sea levels affect marine creatures
doesn’t explain terrestrial (land critters).
Sea level changes due to plate tectonics
(sea floor spreading>) and glacial events.
AGAIN ND pg. 438 Fig. 15-16
Impacts?? Could cause lots of global loss of habitat.
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4) Disease - consider dinosaur extinction. Sea level
lowered and provided land bridges. Problems?? Kind of
like our airlines today. Allows transmission of
diseases.
Some evidence…
a.) Fungal proliferation caused a suppressed
immune system
b.) CT reveal tumors in certain species of
dinosaurs (duckbills)
Avian Flu and humans?
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5) Predation? - possible cause for an interesting
extinction of large Pleistocene mammals
Two ideas for the Pleistocene mammals example:
1.) Changing climate Problems? Too slow.
a.) many large animals went extinct and no plants
b.) mammals should not be so heavily impacted WHY?
c.) glacial retreat should provide more habitat
d.) there were no equivalent extinctions during earlier
phases of ice age.
2.) human radiation (immigration)? Problems?
a.) Calculations show not enough humans to cause the
problem.
EXPLANATION: Ok then what if they decreased
another keystone species?
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Predation? continued
ADD
3.) Another idea for Pleistocene mammal loss.
Those little mammoths found on islands ....hmm…
Wrangel Island
Good explanation of the idea
Mammoths migrated to island and then rising sealevel
isolated them. Through about 500 generations those
that were smaller were more “successful”. WHY?
BUT they seem to have survived out there longer than
other populations of mammoths. So….?
POINT:Concept of hyperdisease hypothesis
We should expect to see evidence of…..
disease in the last generations of mammoths