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105_17-geologic_time - Geologic Time Geologic Time –...

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Unformatted text preview: Geologic Time Geologic Time – Earth: 4.6 billion years old – Vast history recorded in rocks Rock Rock units Fossils Fossils Geologic Geologic events – – – – Deformation Volcanic eruptions Climate changes Mass wasting events Chapter 17 Geologic Time – Relative Dating Sequential Sequential order of events No No ages Changing Concept of Geologic Time – Early Christian Scholars Earth: Earth: 6,000 years old Historical Historical records Genealogies Genealogies in Scripture “Young “Young Earth” theory – Absolute Dating Provides Provides specific dates Radiometric Radiometric dating Really, we use both together! Changing Concept of Geologic Time – George Louis de Buffon (1700’s) French French zoologist Assumed Assumed Earth cooled, hardened from a molten state Melted Melted iron balls of various sizes Allowed Allowed to cool and harden Used Used cooling rate to estimate Earth’s age Calculated Calculated 75,000 years Changing Concept of Geologic Time – Other attempts Sediment Sediment deposition rates – Estimates ranged from <1 million years to > 2 billion years Oceanic Oceanic salinity – 90 million years – Changing to an “old Earth” theory 1 James Hutton – Father of Modern Geology – Scottish geologist – 1726-1797 1726– Established the principle of principle Principle of Uniformitarianism – The processes operating on Earth today are the same as those that have operated throughout geologic time – “The present is the key to the past” – Used to determine how and when rock units and geologic structures were formed uniformitarianism Relative Dating – Uses several principles to determine the sequential order of geologic features Principle Principle of Principle Principle of Principle Principle of Principle Principle of Principle Principle of Principle Principle of superposition original horizontality lateral continuity crosscross-cutting relationships inclusions fossil succession Relative Dating – Principle of superposition Relative Dating – Principle of original horizontality Relative Dating – Principle of lateral continuity 2 Relative Dating – Principle of cross-cutting relationships cross- Relative Dating – Principle of inclusions Relative Dating – Principle of fossil succession Relative Dating – Unconformities Hiatus Hiatus Relative Dating – Unconformities Disconformity Disconformity Disconformity 3 Relative Dating – Unconformities Angular Angular Unconformity Angular Unconformity Relative Dating – Unconformities Nonconformity Nonconformity Nonconformity Relative Dating – Use principles to determine relative ages of all features Relative Dating 4 Correlation – Use: Key Key beds Index Index fossils Subsurface Correlation – Use: Well Well logs Core Core samples Seismic Seismic data Absolute Age Dating Radiometric Radiometric dating – Uses the fact that some elements (like Uranium) are not stable and decay over time – Decay is constant (p,T) Absolute Age Dating Time Uranium U Lead Time Uranium U Lead Half life = half of the radioactive element decayed 5 Geologic Time Chapter 17 6 ...
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