Preparation for Class Discussion on Impacts and Extinction

Perhaps the most well-publicized "hot topic" in Geology has been the debate over possible connections between a large meteor impact event and the extinction of the dinosaurs. While this event (known as the K-T boundary event in geo-parlance) has gotten much of the press, much of the current scientific investigation on this matter relates to other extinction events recorded in the geologic record. Some of these have been minor die-offs within geologic periods, but one, the Permian/Triassic boundary (250 Ma), was even bigger than the K-T: 94% of all species alive in the Permian had disappeared by the Triassic. Geologists are currently trying to discover the different causes for extinctions, as well as the general possiblility of some sort of connection between large impacts and extinction events.

Next week, we'll begin class with a discussion of the impact-extinction relationship. However, to do this, y'all need to know about the effect of massive meteor impacts on the Earth, and about why large numbers of creatures might die away in short periods of time. So, I have listed below is a series of questions. I will assign randomly to each of you one of these questions. What you are to do is go to the Library and/or the Internet and find information to answer the question! Bring the information you've found to class with you on Wednesday (doesn't have to be formal - just some notes for you to work from, and library or Web references that you drew it from. We'll collect your notes at the end of class to make sure you get credit for your efforts),and we'll tally up what we know about big impacts and mass extinctions, and see what we don't know that we need to to understand the issue. This is how scientists approach thorny problems like these!

1) What evidence is there for a massive meteor impact around 66 Ma? [Note that the Chixiculub crater, of K-T boundary extinction fame, was found only in the last few years. Scientists proposed an impact at this time over twenty years ago. Why the delay in finding the crater, and how did they infer an impact without it?]

2) How frequently do very large meteors hit the Earth? Is there any regularity to such large impacts, and if so what causes have been proposed?

3) How frequently have large extinction events occurred on the Earth? Is there a pattern? [Note: to answer this, you will probably need to find out how a large extinction event is defined].

4) Are there any other instances in geologic history when a large extinction event and a large meteor impact have coincided?

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