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Geologic Time and Paleontology

Geologic Time and Paleontology. How Old is the Earth?. Lisa Herzog, Chief Preparator Paleontology and Geology Research Lab. Concepts to Understanding How Old the Earth is . Relative Time.

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Geologic Time and Paleontology

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  1. Geologic Timeand Paleontology How Old is the Earth? Lisa Herzog, Chief Preparator Paleontology and Geology Research Lab

  2. Concepts to UnderstandingHow Old the Earth is

  3. Relative Time • Relative Geologic time has Four Main Principles that refer to sedimentary strata, and a few others that further corroborate the conclusions of deep time. • One of the first main principles is…. Uniformitarianism The present is the key to the past -James Hutton

  4. The Principles ofRelative Geologic Time Principle of original horizontality: Layers of sediment are deposited flat (horizontally)x

  5. The Principles ofRelative Geologic Time Principle of superposition: The older rocks are on the bottom

  6. The Principles ofRelative Geologic Time Principle of crosscutting relationships: Any rock that cuts through another MUST be younger.

  7. The Principles ofRelative Geologic Time Principle of included fragments: ARock that includes fragments of other rock must be younger than the included fragments.

  8. Relative Geologic Time & Fossils Principle of faunal succession specific fossils always appear in the same stratigraphic order in rocks.

  9. Unconformitiesand Correlation • Disconformity – sedimentary layers parallel to each other • Angular unconformity – tilted layers with newer flat material atop • Nonconformity – sedimentary rocks atop igneous or metamorphic rock

  10. Unconformitiesand Correlation • Correlation – matching up rocks of similar age in different locales • Index fossils – accurately indicates the age of a rock • Key bed – a thin, widespread, synchronous sedimentary layer

  11. Absolute Time • In Geology, Absolute Time should be thought of as ‘chronometric’ or ‘calendar’ dating. This is more accurate than the word ‘absolute’ as it inaccurately implies certaintyand precision. • A numeric age of an event is calculated based on radiometric isotope dating. • Absolute dating is the process of determining an approximate computed age.

  12. Chronometric Dating • Measuring absolute age relies on: • Process that occurs at a constant rate • Some cumulative record of that process • Isotopes – radioactive varieties of an element • Vary by the number of neutrons • Half-life – the time it takes for one-half the atoms of a radioisotope to decompose to another isotope or element

  13. Application to Rocks • Age of rock is determined by ratio of parent : daughter atoms • The decay constant must be known • Determines whether half-life is short (min), or long (millions of years) • Rock can be accurately dated if fewer than four half-lives have passed (not enough parent atoms left to measure ratio) • Original rock should not have any daughter atoms present

  14. Common Sources • Carbon-14 • Decays to nitrogen-14 • Present in all living things from plants to animals • Half-life is approximately 5,000 years • Can date fossils and tissues up to 20,000 years old

  15. Common Sources • Potassium-40 • Decays to argon-40 and Calcium-40 • Present in igneous minerals (apatite and muscovite) • Half-life is 1.3 billion years.

  16. Most commonly used isotopes for radiometric dating

  17. Thank You Please remember that no one single piece of evidence proves the time scale, or can definitively place an item/artifact in absolute historical position. All of Geologic time and Paleontology is reliant on the interconnectedness of the data, the principles, and the overall evidence. Lisa Herzog Chief Preparator Paleontology and Geology Research Laboratory

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