Extinction Outline

Fossils continued: radioisotope dating & calibrationCambrian explosionPatterns in the fossil record

Extinction mass extinctions Cretaceous extinction Permian extinction

Next week: human evolution, evolution of disease

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

Extinctions through time: percent of families lost

End Permian

K/T boundary

background extinction

The Cretaceous-Triassic Extinction (K/T)

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?

Initial evidence in favor of asteroid impact

Iridium anomaly77

Ir192.217

If impact, what consequences (and what evidence might be found?)

• Evidence of impact?

• Why would this cause extinctions?

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

Evidence for impact: Ir anomaly

Hallam Fig 8.3

Evidence for impact: tsunami deposits

Fastovksy and Weishampel Fig 18.6

How does an asteroid cause extinction?

• Initial effects (first hour to day):

• Middle-term effects

• Long-term effects

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

• Difficulties of answering!

No loss of diversity until boundary: instaneous death (at least by geological time)

Fastovksy and Weishampel Fig 18.12

Who survived? Who went extinct?

Marine Continental83% planktonic foraminifera 100% non-bird dinosaurs

100% ammonites 100% pterosaurs

93% marine reptiles 56% other reptiles

65% corals 10% flowering plants

All animals > 25 kg

Percent of species extinct at K/T boundary

Ammonite: extinct

Nautiloid: survived

One other great extinction: the end of the Permian

Cause?

Flood basalts

How would volcanic eruptions lead to mass extinction?

How would volcanic eruptions lead to mass extinction?

. . . yet?

– methane (CH4): very potent greenhouse gas [23x as potent as carbon dioxide]

Oligo

Methane and Eocene• 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?

Paleocene

Eocene

Oligocene

Pliocene

Pleistocene

65 mya present

Evidence of warming: 18 O and 13 C

Possible Permian Scenario

Carbon and extinction?

The next mass extinction?

• Habitat destruction

• Global warming, ocean acidification

Increase in diversity after K/T extinction

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 doesn’t heat up the earth.

Taylor, Paul W. (ed). 2004. Extinctions in the history of life. Cambridge University Press.

Study questions1. 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?

Study questions6. Why are duplications of Hox genes thought to be crucial for the

development of bilaterally symmetric animals?