ASTRO-110 Lecture Notes - Lecture 14: Transitional Fossil, Impact Event, Comparative Genomics
9 Sep 2020
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Document Summary
Fossil record shows occasional large dips in the diversity of species. Most recent was 65 million years ago, ending the reign of the dinosaurs. Iridium is very rare in earth surface rocks but often found in meteorites. In 1978 luis and walter alvarez found a worldwide layer containing iridium, laid down 65 million years ago, probably by a meteorite impact. Shocked quartz that requires the high temperatures and pressures of an impact to form. Spherical rock droplets molten rock that solidified while raining down. Meteorite 10 km in size would send large amounts of debris into atmosphere. Debris would reduce sunlight reaching earth"s surface for a few years. Resulting climate change may have caused mass extinction: 75% of all existing plant and animal species. 99% of all living plants and animals. Evidence of large impacts >200 myr ago recycled with seafloor. Impacts large enough to cause mass extinctions are many millions of years apart.
