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15.9: Understanding Earth's History- Challenge 2

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    1. If the same sedimentary rock layer is found on either side of a valley, ___.
    the rocks formed in the same environment, and the valley was cut into the rock later
    2. The principle of original horizontality states that ___.
    sediments are deposited in horizontal layers
    3. If a fault cuts through an entire sequence of rock layers, the fault is ___ than the rock sequence.
    4. If rock P cuts across rock Q, than rock P is ___ than rock Q.
    5. The relative age of a rock is ___.
    the age of the rock relative to other rocks and geologic structures
    6. A key bed must ___.
    be very distinctive
    7. Fossils of microorganisms are called ___.
    8. The thin layer of clay with a high concentration of iridium correlates with ___.
    the extinction of the dinosaurs and other organisms at the end of the Cretaceous
    10. If Earth's history is condensed into one calendar year, dinosaurs appear ___.
    in mid-December
    11. The geologic time scale was originally based ___.
    entirely on relative dating
    12. We live in the Holocene Epoch, which is encompassed by ___.
    the Phanerozoic Eon, the Cenozoic Era, and the Quaternary Period

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