Extinction Outline

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Extinction Outline

• Fossils continued
• radioisotope dating calibration
• Cambrian explosion
• Patterns in the fossil record
• Extinction
• mass extinctions
• Cretaceous extinction
• Permian extinction
• Next week human evolution, evolution of disease

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The story so far . . .

• Earth forms
• First life soon thereafter (ideas, little good
  evidence)
• Multicellular organisms much later needed
  atmospheric oxygen?
• Tremendous increase in animal diversity in
  Cambrian
• Fossils give us a biased, incomplete picture of
  the history of life

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Extinctions through time percent of families lost
End Permian
K/T boundary
background extinction
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The Cretaceous-Triassic Extinction (K/T)

• Initial evidence in favor of asteroid impact
• Iridium anomaly

77 Ir 192.217
Iridium rare on earth, more common in comets
and asteroids Also, more common in magma Or, from
nearby supernova Source massive volcanic
eruptions? Or impact?
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If impact, what consequences (and what evidence
might be found?)

• Evidence of impact?
• Why would this cause extinctions?

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Evidence for impact

• Iridium anomaly found worldwide at K-T boundary
• Shocked quartz in Caribbean and North America
• Evidence for tsunami in North America
• Crater in Yucatan
• Cr isotopes found not volcanic

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Evidence for impact Ir anomaly
Hallam Fig 8.3
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Evidence for impact tsunami deposits
Fastovksy and Weishampel Fig 18.6
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How does an asteroid cause extinction?

• Initial effects (first hour to day)
• Middle-term effects
• Long-term effects

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Were the dinosaurs already dying out? (Or did an
asteroid kill off a dying group?)

• Difficulties of answering!

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No loss of diversity until boundary instaneous
death (at least by geological time)
Fastovksy and Weishampel Fig 18.12
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Who survived? Who went extinct?
Percent of species extinct at K/T boundary

• Marine Continental
• 83 planktonic foraminifera 100 non-bird
  dinosaurs
• 100 ammonites 100 pterosaurs
• 93 marine reptiles 56 other reptiles
• 65 corals 10 flowering plants
• All animals gt 25 kg

Ammonite extinct
Nautiloid survived
13
One other great extinction the end of the
Permian

• Cause?

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Flood basalts
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How would volcanic eruptions lead to mass
extinction?
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How would volcanic eruptions lead to mass
extinction?
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. . . yet?

• methane (CH4) very potent greenhouse gas 23x
  as potent as carbon dioxide

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Methane and Eocene
Eocene
Pliocene
65 mya
present
Paleocene
Pleistocene
Oligocene

• Clathrates frozen water surrounding methane
• Estimate 500 2,500 gigatons (1012 kg)
• If released, could lead to substantial global
  warming
• 55 mya a thaw leading to methane release?

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Evidence of warming ? 18 O and ? 13 C
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Possible Permian Scenario
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Carbon and extinction?
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The next mass extinction?

• Habitat destruction
• Global warming, ocean acidification

Increase in diversity after K/T extinction
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References

• Fastovsky, David E. and Weishampel, David B.
  2005. The evolution and extinction of the
  dinosaurs. Cambridge University Press.
• Hallam, Tony. 2005. Catastrophes and lesser
  calamities the causes of mass extinctions.
  Oxford University Press.
• Kolbert, Elizabeth. 2006. The darkening sea
  what carbon emissions are doing to the ocean.
  New Yorker November 20, 2006. Excellent article
  something more to worry about even if carbon
  dioxides doesnt heat up the earth.
• Taylor, Paul W. (ed). 2004. Extinctions in the
  history of life. Cambridge University Press.

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Study questions

1. If the last fossil is dated to 70 million years
   ago, can we conclude that it went extinct at that
   time? Why or why not?
2. Figure 17.21 shows the pattern of extinctions for
   all organisms. How might the data presented here
   be misleading? (Think about the biases discussed
   in topic 13).
3. How would an asteroid impact lead to extinctions
   of marine organisms? Of terrestrial organisms?
4. How could global warming have led to a mass
   extinction at the end of the Permian?
5. Ammonites and nautiloids are both molluscs with
   chambered shells. Ammonites went extinct at the
   end of the Cretaceous while nautiloids survived.
   Ammonites produce free-swimming young that feed
   at the surface and grow rapidly while nautiloids
   produce a few large eggs that may sit for up to a
   year in the deep before growing slowly. How
   might these differences explain the nautiloids
   survival while the ammonistes went extinct?

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Study questions
6. Why are duplications of Hox genes thought to
be crucial for the development of bilaterally
symmetric animals?