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Unformatted text preview: Chapter 8 Notes Clocks in Rocks o The story of the Earth is contained in the geological record o Geologists use rocks to reconstruct Earths history including:- Cycles (ex Wilson cycle)- Duration/frequency of processes( ex. Floods)- Events (ex. Extinction of dinosaurs) o Relative age- determines if an event is older or younger than another event- From the stratigraphic record o Absolute age- actual number of years elapsed- From radioactive clocks Principles of Stratigraphy o Originally horizontality- Sediments are deposited initially in horizontal beds o Superposition- In undisturbed sedimentary layer, the younger layers are on top and the older layers on the bottom o Faunal Succession- Sedimentary sequences contain fossils in a definite sequence- Layers with the same fossils are the same age Unconformities- Missing pieces of time o Disconformity- Upper layers overlie erosional surface of underformed, still horizontal lower layers o Nonconformity- Upper layers overlie igneous or metamorphic rock...
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- Spring '11