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
The story so far . . .
•Earth forms
•First life soon thereafter (ideas, little goodevidence)
•Multicellular organisms much later –needed atmospheric oxygen?
•Tremendous increase in animal diversity inCambrian
•Fossils give us a biased, incompletepicture of the history of life
Extinctions through time: percent offamilies lost
End Permian
K/T boundary
backgroundextinction
The Cretaceous-Triassic Extinction (K/T)
Iridium: rare on earth, morecommon in comets andasteroids
Also, more common inmagma
Or, from nearby supernova
Source: massive volcaniceruptions? Or impact?
Initial evidence in favor ofasteroid impact
Iridium anomaly
77
Ir
192.217
If impact, what consequences (andwhat evidence might be found?)
• Evidence of impact?
•Why would this cause extinctions?
Evidence for impact
•Iridium anomaly found worldwide at K-Tboundary
•Shocked quartz in Caribbean and NorthAmerica
•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: tsunamideposits
Fastovksy andWeishampel 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 anasteroid kill off a dying group?)
•Difficulties of answering!
No loss of diversity until boundary: instaneousdeath (at least by geological time)
Fastovksy andWeishampel Fig 18.12
Who survived? Who went extinct?
MarineContinental
83% planktonic foraminifera100% non-bird dinosaurs
100% ammonites100% pterosaurs
93% marine reptiles56% other reptiles
65% corals10% flowering plants
All animals > 25 kg
Percent of species extinct at K/T boundary
Ammonite: extinct
Nautiloid: survived
One other great extinction: the endof the Permian
Cause?
Flood basalts
How would volcanic eruptions leadto mass extinction?
How would volcanic eruptions leadto mass extinction?
. . . yet?
–methane (CH4): very potent greenhouse gas[23x as potent as carbon dioxide]
Oligo
Methane and Eocene
•Clathrates: frozen water surroundingmethane
•Estimate 500 – 2,500 gigatons (=1012 kg)
•If released, could lead to substantial globalwarming
•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 diversityafter K/T extinction
References
Fastovsky, David E. and Weishampel, David B. 2005. Theevolution and extinction of the dinosaurs. CambridgeUniversity Press.
Hallam, Tony. 2005. Catastrophes and lesser calamities: thecauses of mass extinctions. Oxford University Press.
Kolbert, Elizabeth. 2006. The darkening sea: what carbonemissions are doing to the ocean. New Yorker November 20,2006. Excellent article: something more to worry about even ifcarbon dioxides doesn’t heat up the earth.
Taylor, Paul W. (ed). 2004. Extinctions in the history of life.Cambridge University Press.
Study questions
1.If the last fossil is dated to 70 million years ago, can weconclude 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? (Thinkabout the biases discussed in topic 13).
3.How would an asteroid impact lead to extinctions of marineorganisms? Of terrestrial organisms?
4.How could global warming have led to a mass extinction at theend of the Permian?
5.Ammonites and nautiloids are both molluscs with chamberedshells. Ammonites went extinct at the end of the Cretaceouswhile nautiloids survived. Ammonites produce free-swimmingyoung that feed at the surface and grow rapidly while nautiloidsproduce a few large eggs that may sit for up to a year in thedeep before growing slowly. How might these differencesexplain the nautiloids survival while the ammonistes wentextinct?
Study questions
6. Why are duplications of Hox genes thought to be crucial for thedevelopment of bilaterally symmetric animals?