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Cosmic Calendar. Reading Rock Records. Telling Time. Relative Time – places events in a sequence but does not identify their actual date of occurrence. Absolute Time – identifies the actual date of an event. Laws .

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telling time
Telling Time
  • Relative Time – places events in a sequence but does not identify their actual date of occurrence.
  • Absolute Time – identifies the actual date of an event
slide5
Laws
  • Law of superposition - states that in a sequence of undisturbed sedimentary rock, the oldest rocks are on the bottom, while the youngest is on the top.
  • Law of cross-cutting – states that an igneous rock is younger than the rock that it has intruded, or cut across
  • Law of included fragments – states that pieces of one rock found in another rock must be older than the rock in which they are found.
  • Unconformity – is a place in the rock record where layers of rock are missing.
geologic timetable
Geologic Timetable
  • EON – the longest segment of time
    • Eras – the segment of time EONS are divided into
      • Periods – era are divided into these
        • Epochs – period are divided into these
how are they formed
How are they formed?
  • Fossils – any evidence of earlier life preserved in a rock.
    • Original remains
      • The actual, unchanged remains – of the plant or animal are preserved.
    • Replaced remains
      • The soft parts of the animal are no longer there, but the hard parts are still visible
    • Molds and Casts
      • Mold is where you have left a hollow depression in the rock
      • Cast is where you have a new mineral fill a mold
    • Trace Fossils
      • Evidence of life other than the remains of a plant or animal
index fossils
Index Fossils
  • Fossils that are used to determine ages of rock that they come from
  • Also known as guide fossils
decaying
Decaying
  • Radioactive Decay
    • When an element loses mass as it ages
  • Half life
    • The rate at which that process happens
  • Radiocarbon dating
    • An isotope that measure the amount of carbon decay
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