Fossils and Paleobiology

When the ammonites disappear absolute age of rocks

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Unformatted text preview: rganisms they host Correlation Fossil organisms can be used to correlate rocks Many geological time points are defined by the organisms found within There are, for example, 67 global ammonite zones for the 55 MYR long Jurassic When does the Cretaceous end? When the ammonites disappear Absolute age of rocks Once we have the relative order of stages, how do we assign absolute dates? Ash beds are used for absolute dates. The rocks they occur in are dated. Fossils are assigned to rocks, not dates. the volcanic ash that might be spilled during the same era as a non- igneous rock, we can date the volcanic ash beds due to the half- lives of radioisotopes. Thus, when we assign fossils to a rock, from then we can find when that rock...
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This document was uploaded on 03/23/2014 for the course BIOL 185 at Georgetown.

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