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Chapter 4. Geological History of Earth

Chapter 4. Geological History of Earth. How to Read Earth’s History. Rocks and Fossils…. Igneous Rock - was once molten and then cooled and solidified Metamorphic Rock - structurally transformed by high pressure or heat, never molten

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Chapter 4. Geological History of Earth

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  1. Chapter 4. Geological History of Earth

  2. How to Read Earth’s History Rocks and Fossils… Igneous Rock - was once molten and then cooled and solidified Metamorphic Rock - structurally transformed by high pressure or heat, never molten Sedimentary Rock- gradual compression of sediments (sand and silt, etc.) Metamorphic rock could be made from igneous or sedimentary rock transformed by heat and pressure; rock types tell formation history; rock mineral contents tell composition

  3. Fossils Created/Survive in Sedimentary Rock Layer by layer of rock is built up- the order of the strata are assumed to correspond to chronological age of the rocks formation This process is “gentle” Process deposits minerals in the organic matter and harden it… such matter is “replaced” by minerals Some mineral rich organic material (bone, teeth, shells) survive mostly intact

  4. Fossil Gallery b) Petrified tree is total mineral replacement c) Impressions- minerals create mold of original organism d) Original organic material –cells dead, but can be studied e) Total preservation- occurs in tree sap (amber) and ice fields

  5. Chronology from Sedimentary Strata

  6. Eons, Eras, and Periods of Earth’s History (hellish) (earlier life) (ancient life) (visible life) (old life) (middle life) (new life)

  7. Absolute Ages Measured Using Radiometric Dating Through a series of radioactive decays, Uranium morphs into Lead! Each step of the reaction had a (statistically) averaged time duration (in individual decays some take shorter and some are take longer than the average).

  8. Dating Game- Counting Half Lifes We assume that all the material was originally pure Parent Isotope when the object formed We then measure the fraction that remains in the Parent Isotope and the fraction that is in the Daughter Isotope. Then using the statistical decay times, called half-life, we estimate the time elapsed from formation

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