Check web page: Updated study questions & HW #1!.
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Transcript of Check web page: Updated study questions & HW #1!.
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Check web page:Updated study questions
&HW #1!
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From Primack, Essential of Conservation Biology
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Permian Extinction
From National Geographic, September 2000
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Species “Life”
From New Scientist 23 October 1999
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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.)
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Proposed Agents of Mass Extinctions
• Changes in climate (global cooling) and sea level (marine regression).
• Asteroid impacts (especially K/T).
• Volcanic eruptions
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Stanley’s research on bivalves during Pleistocene
cold adapted: no changewarm adapted: no change
Gulfstream
cold adapted: no changewarm adapted: declined
Glacier
Climate Change (Glaciation)
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Marine Regression
Continentalshelf: lossof habitat
refuges
Current sea level
Conicalisland: no
loss of habitat
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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.
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Alvarez Hypothesis
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Iridium Profile
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Chicxulub Crater
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Possible Consequences of “IMPACT”!
• Global dust cloud
• Global warming / cooling
• Global wildfires
• Acid rain
• Tidal wave
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Evidence for Alvarez Hypothesis
• 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
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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.
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Volcanic Eruptions
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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.
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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.
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Plants and Mass Extinctions?
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Summary of Mass Extinctions
• Multiple causes:– marine regression– glaciation– asteroids– volcanic eruptions
• Some type of climate change probably always implicated.
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Extinctions Past and Present
• Early mass extinctions
• Blitzkrieg in the Pleistocene
• Recent extinctions