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Updated study questions
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HW #1!
From Primack, Essential of Conservation Biology
Permian Extinction
From National Geographic, September 2000
Species “Life”
From New Scientist 23 October 1999
Background Extinction
• Averaged over the history of life on earth
– 1 species every few years.
• Current expected background rate
– Expected species “life” is 1 – 10 million years.
– Extinction rate between 1 x 10-6 and 1 x 10-7
– 1 to 10 spp. per year (assuming ~ 10 million
spp.)
Proposed Agents of Mass
Extinctions
• Changes in climate (global cooling) and sea
level (marine regression).
• Asteroid impacts (especially K/T).
• Volcanic eruptions
Climate Change (Glaciation)
Stanley’s research on bivalves during Pleistocene
cold adapted: no change
warm adapted: declined
Glacier
Gulf
stream
cold adapted: no change
warm adapted: no change
Marine Regression
Current sea level
Continental
shelf: loss
of habitat
refuges
Conical
island: no
loss of habitat
Climate Change Evidence
• Glaciation associated with Ordovician ME.
• Equivocal evidence for global cooling during
Devonian, Cretaceous, and Permian ME’s.
• No major glaciation associated with Triassic ME.
• A major glaciation ca. 300 million years ago and
lasting 90 million yrs did not result in an ME.
• Tentative Conclusion: glaciations are not currently
regarded as a necessary cause for ME’s.
Alvarez Hypothesis
Iridium Profile
Chicxulub Crater
Possible Consequences of
“IMPACT”!
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•
•
•
•
Global dust cloud
Global warming / cooling
Global wildfires
Acid rain
Tidal wave
Evidence for Alvarez Hypothesis
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•
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Iridium and shocked quartz at KT boundary.
Chicxulub crater
Synchronicity in Cretaceous extinctions (?)
Tentative Conclusion: Almost certainly
implicated at least in part with Cretaceous
extinction
Evidence for Impact Extinctions
• Strong evidence for Cretaceous ME
• Associated with Permian ME
• Several impact events NOT associated with
ME’s.
• Tentative Conclusion: Does not appear to be
a general explanation for ME’s.
Volcanic Eruptions
Volcanic Eruption Hypothesis
• Eruptions boost greenhouse gasses.
• Global warming releases sub-sea-floor
methane, further increasing global warming.
• The heat itself might drive species to
extinction.
• The altered climate might induce changes in
ocean circulation, biological productivity
and ultimately cause oceanic anoxia.
Evidence for Volcanic Eruptions
• Associated with Cretaceous, Triassic, and
Permian ME’s.
• Triassic ME has no sign of methane.
• Significant lava flows 120 MYBP
associated with methane release but no ME.
• Tentative Conclusion: More work is needed
to assess this hypothesis – especially
relevant to current climate change.
Plants and Mass Extinctions?
Summary of Mass Extinctions
• Multiple causes:
–
–
–
–
marine regression
glaciation
asteroids
volcanic eruptions
• Some type of climate change probably
always implicated.
Extinctions Past and Present
• Early mass extinctions
• Blitzkrieg in the Pleistocene
• Recent extinctions