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19.1 The Fossil Record

19.1 The Fossil Record. TRILOBITE - early arthropod - EXTINCT!. Fossil - preserved remains of ancient life - found in sedimentary rock - studied by paleontologists (“old”). Sedimentary rock - formed as small particles settle on bottom of ocean, lake or river.

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19.1 The Fossil Record

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  1. 19.1 The Fossil Record TRILOBITE - early arthropod - EXTINCT!

  2. Fossil - preserved remains of ancient life - found in sedimentary rock - studied by paleontologists (“old”)

  3. Sedimentary rock - formed as small particles settle on bottom of ocean, lake or river

  4. Older rock layers usually deeper in earth

  5. Fossils form as organic material replaced by minerals (“petrified”) “petro” = wood

  6. Relative dating - places rock layers in a temporal sequence based on depth

  7. Index fossil - easily recognizable organism that only lived for a short time • They help compare rock ages TRILOBITE = 540 mya

  8. Radiometric Dating - dates rock based on decay of radioactive isotopes. • Radioactive isotopes (such as K-40) break down at a steady rate.

  9. Half life = approx. amt. of time for ½ of isotope to decay into daughter nuclei • K-40 = 1.3 billion years • C-14 = 5,730 years

  10. Scientists measure amount of remaining radioactive isotope and compare it to original amount to age rocks and fossils • Ex) Potassium-40  Argon-40 • Argon gas gets trapped in the rock

  11. Geologic Time scale • EON • ERA • Period

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