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Fossilization and Rock Dating

Fossilization and Rock Dating. Fossils. 99.999% of organisms do not become fossils, instead they decompose Fossil = preserved remains of ancient organisms Usually found in sedimentary rock. Fossils. Conditions needed for fossilization: Made of hard parts (bone, shell)

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Fossilization and Rock Dating

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  1. Fossilization and Rock Dating

  2. Fossils • 99.999% of organisms do not become fossils, instead they decompose • Fossil = preserved remains of ancient organisms • Usually found in sedimentary rock

  3. Fossils Conditions needed for fossilization: Made of hard parts (bone, shell) Quickly buried (mud, sand, volcanic ash) Die in a low oxygen environment Very specific criteria!! This is the reason why the fossil record is biased!!

  4. Fossils Types: Petrified (wood, old bones) 2. Frozen (mammoths via glaciers)

  5. Fossils 3. Molds and Casts -impressions left = mold - impressions filled = cast 4. Amber - tree resin (sap) traps bugs, pollen, small animals and turns to rock (Jurassic Park)

  6. Fossils 5. Asphalt/Tar - oil near surface (saber tooth tigers, giant sloths) 6. Coprolites - fossilized excrement (can determine size and diet)

  7. Rock Dating • Earth has changed through time!! • Geologic record preserved in rock gives us the evidence • Need to look through rock layers (strata) to decipher age relationships between rocks and fossils

  8. Rock Dating Methods of dating rock and fossils include: Relative Dating Absolute/Radiometric Dating

  9. Rock Dating Relative Dating - use of location of rock layers to determine age - law of superposition = lower strata are older while younger strata are higher up if strata are horizontal - not as accurate

  10. Rock Dating • Index/Guide Fossils • Useful when trying to determine the age of a rock • Each fossil assemblages stay in similar aged strata

  11. Rock Dating 2. Absolute/Radiometric Dating - using radioactive isotopes found in rock to determine a rock or fossils age - very accurate but must use correct isotopes and half-life

  12. Rock Dating • Half-life • Radioactive isotopes decay over time • Decay rate depends on each isotope • Half-life = the number of years it requires for half of radioactive isotopes to decay

  13. Rock Dating • Radioactive isotopes commonly used: • Carbon-14 (5,730 yrs.) • Potassium-40 (1.227 billion years) • Rubidium-87 (48.8 billion years)

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