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Cretaceous-Tertiary Extinctions
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Lecture 25
5/11/98
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| | The Cretaceous-Tertiary extinctions resulted in the extinction of the dinosaurs and many other groups. As a result it opened environments and paved the way for modern floras and faunas. |
| | The Cretaceous-Tertiary extinctions are one of the major extinction events in the history of life |
| | Unlike the Permian-Triassic extinctions, the Cretaceous-Tertiary extinctions appear to be sudden. |
| | An asteroid impact at the time appears to have played a major role in the extinction. |
| | 15% of all marine families |
| | 50 % at generic level, maybe 80-90 % of all species |
| | concentrated on planton, marine predators, and shallow water communities |
| | 25 % of terrestrial families |
| | nothing bigger than 25 kg survived |
| | Appears to be very sudden |
| | The Cretaceous-Tertiary boundary sediments |
| | well described around the world |
| | can be shown to be a single bed |
| | A wide range of suggested |
| | climatic change to dinosaur blindness |
| | several events took place at or near the boundary |
| | Discovery of irridium in boundary clay |
| | Similary deposits were found world wide |
| | Other materials in the boundary layer |
| | Irridium is rare on the surface of the earth |
| | Irridium is much more common in space |
| | Discovery of an Impact Crater |
| | Chicxulub Impact structure |
| | Buried beneath the Yucatan Peninsula |
| | Age dates of melt rock in the structure have at date of 65 Ma |
| Did the Impact cause the extinctions? |
| | This remains an issue of contention |
| | You must explain all of the extinctions |
| | We don't understand all of the implications the event |
| | Impact wipes out most plankton & primary production |
| | This lose travels up the food chain and heavily impacts top order consumers |
| | Smaller organisms may survive by burrowing, hibernating, or migrating |
| | Shallow marine faunas hit by acid rains and temperature changes |
| | Plants & planton return from resting spores & seeds to repopulate planet. |
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