The Fossil Record

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The Fossil Record

  1. 1. The Fossil Record Def: the traces or remains of animals or plants from a previous geologic time.
  2. 2. Paleontologist <ul><li>Study fossils to learn about past geologic events, climates, and evolution. </li></ul>
  3. 3. Most fossils are found in sedimentary rock… <ul><li>Cover a dead object without damaging it. </li></ul><ul><li>Keep other animals from destroying “potential” fossils. </li></ul>keichosaurus
  4. 4. No fossils in igneous or metamorphic rocks !? <ul><li>Living things covered with hot, molten lava tend to burn up… </li></ul><ul><li>… and fossils in metamorphised rocks become pressured/heated beyond recognition. </li></ul>
  5. 5. <ul><li>Usually, only the HARD parts of an organism are preserved…bones, shells, teeth. </li></ul><ul><li>Sometimes, only a replica of the organism remains. </li></ul>
  6. 6. Normally… <ul><li>Dead plants & animals are usually eaten by other animals or decomposed by bacteria before they can become fossils. </li></ul><ul><li>Only dead orgs that get buried quickly by sediment stand a chance of getting preserved as fossils. </li></ul>
  7. 7. Types of Fossilization
  8. 8. Mummification <ul><li>Organisms become dried out. </li></ul><ul><li>Usually found in desert caves or buried in desert sand. </li></ul><ul><li>Org doesn’t rot : bacteria need moisture to “work.” </li></ul>
  9. 9. Amber <ul><li>Hardened tree sap. </li></ul><ul><li>Delicate structures preserved (legs, antennae) </li></ul><ul><li>DNA has been extracted from these fossils… </li></ul>
  10. 10. Tar Beds <ul><li>Pools of “black gold” at the Earth’s surface usually covered by water. </li></ul><ul><li>Animals come to drink, get stuck in the tar, and get sucked in… </li></ul>La Brea Tar Pits in L.A.
  11. 11. Freezing <ul><li>Low temps of frozen soil & ice protect & preserve organisms. </li></ul><ul><li>Org doesn’t rot: bacteria can’t survive freezing temps. </li></ul><ul><li>Rhinos, mastodons, mammoths found in Alaska & Siberia. </li></ul>
  12. 12. Petrification <ul><li>Mineral-rich groundwater removes & replaces the original mineral with a harder mineral (such as silica, calcite, pyrite). </li></ul><ul><li>Petrified wood! </li></ul>
  13. 13. Traces of Organisms <ul><li>TRACE FOSSILS such as tracks, footprints, borings, and burrows can provide information about organisms. </li></ul>
  14. 14. Imprints <ul><li>Leaves, stems, shelled creatures, flowers, fish… become stuck in soft clay and leave an imprint which shows the surface features of the organism. </li></ul>
  15. 15. Molds <ul><li>An organism gets buried in soft sediment… </li></ul><ul><li>… its remains decay, leaving an empty space…a “bubble” of nothing in the shape of the organism </li></ul><ul><li>A mold retains the shape & exterior markings of the org, but tells us zero about the “insides.” </li></ul>
  16. 16. Casts <ul><li>When sand or mud gets inside a mold & hardens, a cast is formed. </li></ul><ul><li>A cast is a replica of the outer surface of the original org. </li></ul>Montana Rhinos
  17. 17. Index Fossils <ul><li>Certain fossils are found only in the rock layers of a particular geologic age. </li></ul><ul><li>These are known as INDEX FOSSILS. </li></ul>Paradoxides :Cambrian Era
  18. 18. To Qualify as an Index Fossil: <ul><li>Must be “world-wide.” </li></ul><ul><li>Must be distinctive. </li></ul><ul><li>Must have a “short” life span. </li></ul><ul><li>Must be numerous! </li></ul>Echioceras: Jurassic Period

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