ESS104H1 Lecture 8: Lec 8. Mass Extinctions
Document Summary
For a long time geologists couldn"t tell the actual age, they only knew the relative age. Many geological periods were divided up and named based on species that lived during them. Base or beginning is based on the radiation of species (begins and starts to spread)and end is marked by the end of a species (no longer in geologic record). When we see hiatus (break or catastrophe) it indicates: i. ii. Sea level has dropped: you might not be depositing rocks, sediments that will eventually become sedimentary rocks. Things that makes sea level drop: glaciation (sea levels go way down and continental shelves are exposed). If sea level rises again, new fossils can be deposited, new creatures can come in and colonize areas that were previously uninhabitable. Single bedding plane could represent a million years of deposition. Or thick layer with only a year od deposition.
