Popular in Geological Hazards and Their Human Impact
Popular in Geology
This 1 page Class Notes was uploaded by Erika Marini on Sunday April 24, 2016. The Class Notes belongs to Geol113 at University of Delaware taught by McGeary,Susan in Spring 2016. Since its upload, it has received 4 views. For similar materials see Geological Hazards and Their Human Impact in Geology at University of Delaware.
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Date Created: 04/24/16
Deep Time 04/19/2016 ▯ How old is old? How old are geologic events and how do geologists find out? ▯ Geologic time: Relative Age dating: may no know exact day, but can put events in order of a sequence Absolute (Numerical): put actual dates ▯ Marine Sedimentary Rocks: Successive horizontal layers forming on the bottom of the ocean Younger layers form on top of older layers ▯ Principles of Relative Age Dating: Superposition: younger sedimentary rocks are on top of older sedimentary rocks Original horizontality: sedimentary rocks are deposited in flat sheets Lateral continuity: sediments generally accumulate in continuous sheets Cross cutting Relationship: Geologic events that cut across pre- existing rocks are younger than the rocks that they cut. o Fault o Volcanic intrusion Inclusions: If layer A contains fragments of layer B, then B must be older Fossil Selection: there is a sequence of fossils that we use to put different rock layers in their true relative sequence Fossil Succession: certain fossils are ALWAYS observed in the same sequence in sedimentary rocks o Fossils are found within a given time interval-“geologic range”- in the rock record Cenozoic era-65 MYA Mass extinction- “new life” canids, felines, whales, primates Mesozoic Era- 25 MYA Mass extinction- “middle life” reptiles, early mammals and birds, dinosaurs, flowering plants, grasses Paleozoic Era- 542 MYA Appearance of shells Numerical Dating: Mostly based on unstable elements that undergo radioactive decay (at known rates) Isotopes: Parent isotope: decays to form daughter product Half-life: the time is takes for ½ of the isotope to decay into the daughter product ▯ ▯
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