Time is not part of rock cycle, but is implied
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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

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.


Time is not part of rock cycle but is implied







Time is not part of rock cycle but is implied

Event Principle

Deposition of 1 – 5 Superposition

Folding of 1 – 5 Original Horizontality

Erosion Superposition / Cross-cutting

Deposition of 7 – 9 Superposition

time


Time is not part of rock cycle but is implied

Layer H

Layer F

Layer G

Layer E

Layer D

Layer C

Layer B

Layer A

Figure 18.4

.5


Time is not part of rock cycle but is implied

Uranium-238

Unstable parent

Rn-222

Radon gas

Lead 206

Stable daughter




Radiometric dating example 1
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?


Radiometric dating example 11
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


Radiometric dating example 2
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?


Radiometric dating example 21
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%?


Time is not part of rock cycle but is implied

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


Time is not part of rock cycle but is implied

Correlation: establishing equivalence

between rock layers that were once

continuous