chapter 8 - Grotzinger Jordan Press Siever Understanding...

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Understanding Earth Chapter 8: CLOCKS IN ROCKS Timing the Geologic Record Grotzinger • Jordan • Press • Siever (formed in an ocean)
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Why Understand (Geologic/Deep) Time? Earth History Continental Growth Plate Tectonics Resources Planetary Evolution Biological Evolution Rates of Evolution Geohazards Climate
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Human history contains some useful information on very recent events (miniscule fraction of Earth’s history)
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Relative vs. Absolute Time RELATIVE TIMING and CORRELATIONS • Stratigraphy • Relative events/rock types • Fossils ABSOLUTE TIMING • Radiometric dating Relative : the occurrence of one event/rock relative to another Absolute : the age of an event/rock in years in the past (Ka, Ma, Ga)
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Original Horizontality: Most rocks that form at the Earth's surface are deposited in essentially horizontal layers. Therefore, when layered rocks are not horizontal, they probably have been affected by post-depositional processes such as a tectonic event. Superposition: When layered rocks are formed, they are deposited in an orderly sequence with the oldest being at the base of the sequence and the strata becoming progressively younger upward. Therefore when a sequence of rocks differs from the predicted sequence, or layers are missing, then an explanation for the cause of these differences is required. Cross-cutting Relationships: Features such as faults or igneous intrusions generally cross-cut or affect all rocks that were present locally at the time of the faulting or intrusive event. Uniformitarianism: Present Earth processes are useful in understanding the types and rates of processes that have affected the Earth during past periods of geologic history . Geologic Time Principles Several geologic principles are fundamental to using the rock record to interpret processes.
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Geological Time (sometimes called “deep time”) *see handout about what you need to know, e.g. tests Note many graphics of the geologic time scale are not “to scale”
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This note was uploaded on 07/15/2009 for the course GEO 80355 taught by Professor Kyle during the Spring '09 term at University of Texas at Austin.

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chapter 8 - Grotzinger Jordan Press Siever Understanding...

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