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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

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)

Marine Regression

Continentalshelf: lossof habitat

refuges

Current sea level

Conicalisland: 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”!

• Global dust cloud

• Global warming / cooling

• Global wildfires

• Acid rain

• Tidal wave

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

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