Science, Creation & EvolutionThe dangers of EvolutionNot meant as a criticism I acknowledge that we all make mistakes in spellling and grammar, but we should also be willing to accept corrections (myself included). Well, geologic boundaries (especially stage boundaries) are typically defined by first and or last appearance of certain taxa (organisms). Usually, someone notices a marked change in the biological content of a rock, looks for it elsewhere in the geological record and then gives it a name. The name Frasnian comes from the location in Belgium (Frasnes) where the rocks were first described and also the name Fammenian comes from the village of Famenne in Belgium. The taxanomic changes between the two rock sections were used to define the boundary. I also want to make sure that I don't leave you with the impression that geochemistry is of no use because it is. Once the boundary was defined and the extinction event was noted, it becomes important to try and figure out why this particular extinction was so severe. Geochemical markers become important in identifying possible causes for the extinction. The most famous geochemical marker is the Iridium anomaly at the Cretaceous-Tertiary boundary because it is linked to the demise of the dinosaurs via meteor collision. -E |
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