GEOLOGY STUDY GUIDE 3 - Chapter 9 Geologic Time(sections...

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Chapter 9 – Geologic Time (sections from the book: all) Some key terms or ideas: Relative-age dating Rocks placed on timescale in sequence of formation Law of superposition In undisturbed rock layers, oldest are on the bottom (Nicholas Steno) Principle of original horizontality Layered strata are deposited horizontally or nearly horizontally Principle of lateral continuity Principle of fossil succession Different strata contain different fossils, there is an order of fossils/strata, use fossils to correlate formations from different outcrops Principle of cross-cutting relationships When magma intrudes and crystallizes, it is younger than the rocks affected Unconformity Surface that represents a break in the rock record due to erosion or nondeposition Disconformity Nonconformity Separates older igneous/metamorphic rocks from younger, sedimentary rocks Angular unconformity Sediments deposited, folded/deformed, erosion, horizontal layers pile on top Absolute-age dating (radiometric dating) Determine age in number of years by measuring amount of radioactive elements and the rate at which they decay. Radioactivity Energy and subatomic particles released when one element changes to another Doesn’t work for every rock: sedimentary, metamorphic (reset), weathered rocks Half life Time required for half of parent atoms to decay into daughter atoms Parent / daughter ratio, etc. Parent- radioactive element Daughter- stable, non-radioactive element Some key questions or concepts: Describe how the order of geologic events can be determined Describe how geologists determine the relative ages of rocks in widely separated places Describe how geologists recognize gaps in the rock record Determine the order of geologic events from a diagram or picture of a rock sequence Explain the process of radioactive decay, and describe how radioactive isotope abundances change over time Define the concept of half-life Apply the concept of half-life to determine the age of a rock, given modern isotopic abundances of a radioactive element and the half-life for decay of that element
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This note was uploaded on 06/19/2008 for the course GEOL 1010 taught by Professor Pranter,ma during the Fall '07 term at Colorado.

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GEOLOGY STUDY GUIDE 3 - Chapter 9 Geologic Time(sections...

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