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Time is not part of rock cycle, but is implied

Time is not part of rock cycle, but is implied. Example : a granite could be weathered and the particles eventually become part of a sandstone. The sandstone could later be metamorphosed to become a quartzite. How fast these events happen would determine what ages the rocks were.

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Time is not part of rock cycle, but is implied

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  1. Time is not part of rock cycle, but is implied Example: a granite could be weathered and the particles eventually become part of a sandstone. The sandstone could later be metamorphosed to become a quartzite. How fast these events happen would determine what ages the rocks were.

  2. RELATIVE DATING OF GEOLOGIC • EVENTS / MATERIALS: • PRINCIPLES • Superposition • Original Horizontality • Cross-cutting relationships

  3. Superposition

  4. Original Horizontality

  5. original horizontality

  6. Erosion and creation of unconformity

  7. Cross-cutting relationships

  8. Event Principle Deposition of 1 – 5 Superposition Folding of 1 – 5 Original Horizontality Erosion Superposition / Cross-cutting Deposition of 7 – 9 Superposition time

  9. Layer H Layer F Layer G Layer E Layer D Layer C Layer B Layer A Figure 18.4 .5

  10. Uranium-238 Unstable parent Rn-222 Radon gas Lead 206 Stable daughter

  11. Example radioactive decay pairs

  12. Figure 18.14

  13. radiometric dating – example 1 • A granite is collected and analyzed • Contains 50% U-235 and 50% Pb-207 • Half-life of U-235 is 713 million years • How old is the granite?

  14. radiometric dating – example 1 • Refer to Figure 18.14 • 50% parent, 50% daughter corresponds to 1 half-life • Half-life of U-235 is 713 million years • Thus, granite is 713 years old

  15. radiometric dating – example 2 • A granite is collected and analyzed • Contains 2 micrograms of U-235 and 6 micrograms of Pb-207 • Half-life of U-235 is 713 million years • How old is the granite?

  16. radiometric dating – example 2 • 8 micrograms of parent + daughter • 2/8 micrograms = 1/4 = 25% U-235 • 6/8 micrograms = 3/4 = 75% Pb-207 • Refer to Figure 18.14 • 25% parent / 75% daughter corresponds to 2 half lives. • Half-life of U-235 is 713 million years • Thus, granite is 2 x 713 = 1,426 million years old = 1.4 billion yrs. • What if U-235 = 75%, Pb-207 = 25%?

  17. Europe Modern humans Present time Asia 13,000 years Archaic humans incl. Neanderthals 33,000 years Small Archaic Humans 95,000 years Evolution of humans ~3 million years ago Africa

  18. Correlation: establishing equivalence between rock layers that were once continuous

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