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Geologic Time

Geologic Time. An introduction. Which elephant is older????. Oldest. Youngest. These two questions are related to relative time versus absolute ages. Relative time : Which elephant is oldest? Youngest? Absolute age: How old is the oldest elephant? Youngest?. Born in 1970. oldest.

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Geologic Time

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  1. Geologic Time An introduction

  2. Which elephant is older????

  3. Oldest Youngest

  4. These two questions are related to relative time versus absolute ages. • Relative time: Which elephant is oldest? Youngest? • Absolute age: How old is the oldest elephant? Youngest? Born in 1970 oldest Born in 1999 youngest

  5. Rocks Record Earth’s History • Rocks record geological events and changing life forms of the past • We have learned that Earth is much older than anyone had previously imagined and that its surface and interior have been changed by the same geological processes that continue today.

  6. The same two questions are frequently asked in the geosciences. Relative time: Which rock unit is oldest? Youngest Absolute age: How old is the oldest rock unit? Youngest? younger 375 Ma older 975 Ma I made these dates up!

  7. Three terms • Strata-layers of rock • Stratigraphy- science of studying, describing, and correlating strata • Stratigraphic Column- An ordered sequence of strata.

  8. Discovering Earth’s History • Uniformitarianism means that the forces and processes that we observe today have been at work for a very long time.

  9. Law of Superposition • In an undisturbed rock sequence, younger rocks are found on top of older rocks.

  10. Unconformity • An unconformity represents a long period during which deposition stopped, erosion removed previously formed rocks, and then deposition resumed.

  11. Principle of Cross-Cutting Relationships • The principle of cross-cutting relationships states that when a fault cuts through rock layers, or when magma intrudes other rocks and crystallizes, we can assume that the fault or intrusion is younger than the rocks affected.

  12. Principle of Cross-Cutting Relationships

  13. Another Example Oldest to Youngest 1,2,3,4,5

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