Earth_history__absolute_and_relative_dat

Earth_history__absolute_and_relative_dat - Geologic time...

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Geologic time Absolute dating : determination of a numerical date for a rock or an event, only became possible in the XX century Relative dating : placing rocks and events in order from oldest to youngest or vice versa
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Uniformitarianism : physical, chemical and biological laws that operate today also operated in geologic past. All changes were slow and gradual. ‘Present is a key to past’ Navajo Sandstone (left) was interpreted as dune deposit based on observations in modern deserts
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Competition of ideas: catastrophism or uniformitarianism? Catastrophism : Earth was shaped by sudden and violent cataclysms, very little change took place in between Examples of catastrophic events: asteroid impacts, mass extinctions, eruptions of supervolcanoes
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Relative dating is based on 1 . Law of Original Horizontality- Sedimentary strata and lava flows are deposited in horizontal sheets. If these layers are not horizontal, subsequent movements have occurred. 2. Law of Lateral Continuity- Strata and lava flows extend laterally in all directions and pinch out at the edge of their deposition. 3. Law of Superposition- In an undisturbed sequence of strata or lava flows; each layer is older than the one above and younger than the one below. 4. Law of Inclusions- Inclusions are rock & mineral fragments contained in another rock type. Any inclusion is older than the rock that contains it. 5. Law of Cross-Cutting – Any feature that cuts across a rock or sediment must be younger than the rock or sediment through which it cuts. Examples: faults, unconformities and igneous intrusions. 6. Law of Unconformities- Unconformities represent gaps in geologic time when layers were not deposited or when erosion removed layers. a. Disconformity-Unconformity between parallel layers b. Angular Unconformity-Tilted strata are overlain by younger more parallel strata. c. Nonconformity-Sedimentary layers deposited on igneous or metamorphic rock. 7. Faunal Succession- Fossil organisms succeed one another in a definite, irreversible, and determinable order. 8. Index Fossils- Used to correlate rock sequences from different locations. a. Must have lived for a short geologic period of time. b. Must have had a wide geographic range. c. Must be easily identified. 9. Correlation - matching of rocks of similar age in different regions.
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Nicolas Steno (born Dutch, 1638-1686) Established three principles of relative dating: - Superposition - Original horizontality - Lateral continuity Abraham Gottlob Werner (1749 or 1750 – 1817) Germany trained in law and mining Famous geology teacher, founder of Neptunism All rocks were formed in the ocean and Precipitated from water. Major controversy involved the formation of igneous rocks that he believed also took place in the ocean.
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James Hutton (1726-1797)
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This note was uploaded on 04/15/2009 for the course EARTH 122 taught by Professor Calia during the Winter '08 term at Waterloo.

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Earth_history__absolute_and_relative_dat - Geologic time...

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