CHAPTER 8-THE ROCK RECORD GRAND CANYON VIDEO GRAND CANYON VIDEO How can we determine ages of rocks...
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Transcript of CHAPTER 8-THE ROCK RECORD GRAND CANYON VIDEO GRAND CANYON VIDEO How can we determine ages of rocks...
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CHAPTER 8-THE ROCK RECORD GRAND CANYON VIDEO
How can we determine ages of rocks and the Earth?
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Uniformitarianism: a principle that geologic processes that occurred in the past can explain current geologic processes-presented by James Hutton in the 18th century
Section 1: Determining Relative Age
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•Geologists estimate that the Earth is about 4.6 billion years old•Hutton’s work forced geologists to revise the estimated age-it was once believed to be only about 6,000 years old.
Earth’s Age
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•Rocks form in layers (strata)•Indicates age of rock relative to other layers of rock
Relative Age
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Undeformed rock layers of sedimentary rock-older layers on bottom
Law of Superposition
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Sedimentary rocks left undisturbed will remain in horizontal layers
Principle of Original Horizontality
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•Graded bedding-sediments settle according to particle size-if large particles are on top, the layers have been disturbed•Cross beds-slanted layers can be used to determine the original position of layers•Ripple marks-formed by wind or water and preserved in rock. Ripples point upwards and indicate original position of rock
Other clues about age, see pg. 204 in text
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A break in the geologic record due to movement in the earth’s layers. Types:•Nonconformity•Angular unconformity•Disconformity
Unconformities, see pg. 205
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A fault or a body of rock that cuts through another rock layer is younger than that layer (it formed after the layer it cuts through)
Crosscutting Relationships
Relative Age Video Clip