chapter 8-lecture

chapter 8-lecture - Chapter 8 The Rock Record and the...

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Chapter 8 The Rock Record and the Geologic Time Scale This week’s assignment: read chapter 8
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Outline I. The doctrine of uniformitarianism II. Two kinds of geologic time scale A. Relative time scale 1. Principle of original horizontality 2. Principle of superposition 3. Faunal succession 4. Deformation and uncomformities 5. Cross cutting relationships B. Absolute time scale 1. Radiometric dating 2. Age of the Earth
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III. The geologic timescale A. Precambrian eons Hadean Archean Proterozoic B. Phanerozoic eon Paleozoic era Meszoic era Cenozoic era
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Doctrine of Uniformitarianism formulated by James Hutton, 1785. The processes now operating to modify Earth’s surface, has also operated much the same throughout the geologic past. There is a uniformity of processes past and present. The present is the key to the past.
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Different rates of geologic processes
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Principles used for relative dating 1. Principle of original horizontality: sediments are deposited under gravity as horizontal beds 2. Principle of superposition: if any undisturbed sequence of rock strata, the youngest stratum is at the top and the oldest is at the bottom.
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The Grand Canyon Sequence The sedimentary rocks are from 550 to 250 million years old.
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2. Priniciple of fauna succession (fauna= animal species) Fossil ammonite Life forms have changed through times from simple to complex; there is a definite succession of life Therefore fossils (shells, teeth, bones, impressions, tracks) can be used to date the relative ages of sedimentary rocks.
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A very ancient fossil: trilobites in 305 million years old rock. Trilobites are from the Cambrian to Permian periods (250-543 million years ago)
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Faunal succession William Smith first observed different layers of rocks contained different groups of fossils. Exposed rocks (outcrops) in different locations can be correlated according to their fossils.
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Geologic time scale Fossils provide a basis for establishing the relative age of sedimentary rocks and correlating rock layers exposed at different locations The result is a geologic time scale for the entire earth.
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3. Unconformity A time gap in the geologic record is called
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This note was uploaded on 05/04/2008 for the course GEOL 1001 taught by Professor Baksi during the Fall '07 term at LSU.

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chapter 8-lecture - Chapter 8 The Rock Record and the...

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