Exercise: Extinction Hypotheses




BIO372 : Extinction : Mass Extinctions : Exercise: Extinction Hypotheses

Exercise: Extinction Hypotheses

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The discovery of dinosaur fossils made it clear that the earth has not always been the way it is today. What was responsible for the changes that made vast arrays of organisms go extinct? Are those changes relevant for us?

Two of the primary explanations of the mass extinctions and the associated biological transitions at the Cretaceous-Tertiary boundary are represented in the hypotheses of meteorite impacts and of widespread volcanism.

There must be consistency between the series of events that each hypothesis suggests and the facts that are known: fossils, signs of meteorite impacts, indications of volcanic eruptions, and our understanding of the way the world works.

There is evidence relevant to these hypotheses, but so far the evidence cannot conclusively distinguish between the alternatives. Are there implications, or predictions, of these alternative hypotheses that will help us decide?

1. There were three hypotheses offered in the readings that suggested how the path of a comet (or giant asteroid) could have coincided with the orbit of the earth. What were they?

2. What is the evidence that earth did receive visits from asteroids or meteorites in its past?

3. If volcanism could have been responsible for a global catastrophe, it must have been large and occurred at the K-T boundary. What is the evidence for this?

4. Volcanism is an activity that originates on earth today. What causes a volcano to erupt?

5. The discussion of the asteroid impact hypothesis in the readings described a global cooling as a result of debris tossed into the stratosphere from the impact. The volcanic hypothesis offered by Dewey McLean predicts a greenhouse effect following the K-T volcanism. Are these predictions definitive, i.e., could there have been warming after an asteroid impact or cooling after volcanism? Explain.

6. There is currently a steady increase in CO₂ concentration in earth's atmosphere.

a) If significant atmospheric warming, e.g., from large increases in CO₂, can exterminate species, what is the chance that we are either in or approaching another mass extinction? Explain.

b) Is the potential extinction of species from warming of earth's climate a catastrophe we can do something about? What would (could) you do to ameliorate such a crisis from this or some other cause?

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