Plate Tectonics

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Plate Tectonics

• Relative Dating and Rock Layers

http//www.youtube.com/watch?v_mcC8kFacrk
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Earths History
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How old is our Universe?
13.7 billion years old
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How old is Earth?
4.6 billion years old
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Earth was once made of molten lava and magma,
eventually cooling to form igneous rock
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Weathering, Erosion, Compaction, Cementation,
Heat, and Pressure eventually formed the rocks
that cover our Earths surface.
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What we know about Earths history comes from
studying its rocks, rock formations, rock layers,
and even the rocks from outer space
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Meteorites

• 5. All meteorites formed about the same time that
  Earth formed, so studying them helps us study
  Earth.
• 6. Meteorites have not been affected by erosion,
  weathering or other forces the way Earths rocks
  have.

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Studying Earths Rocks
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Rock Layers

• Which book was placed here first?
• The bottom one!
• 7. When rocks form, the oldest ones are usually
  found beneath younger rocks

http//www.youtube.com/watch?v9Df4CtlZ0AQ
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Fossils

• 8. Most fossils are found in Sedimentary rock
  layers
• Why?
• Heat, pressure, and melting would probably
  destroy fossils during the formation of Igneous
  and Metamorphic rocks

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• 9. Sedimentary rocks, and the fossils they trap,
  are often found in layers, oldest rocks are found
  on the bottom.

http//www.prehistoricplanet.com/news/index.php?id
48
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• 11. Digging through the layers of rocks, helps us
  understand more about the history of Earth.

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• 12. The Grand Canyon (Arizona) was carved by the
  Colorado river, exposing millions of years worth
  of rock layers.

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13. Sometimes, the rock layers arent always
horizontal
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14. And sometimes ocean fossils are found high in
the mountains
Why?
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• 15. Turns out, our Earths surface is constantly
  shifting, changing, and eroding.
• And the layers get pushed around.

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• 16. Only in the last 200 years, have we begun to
  understand the structure, formation and history
  of our Earth.

I wonder whats inside Earth?
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Relative Age of Rocks

• To figure out the ages of rocks and their
  fossils, geologists rely on a few rules

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Law of Superposition

• In any undisturbed rock, the oldest layer is at
  the bottom and the youngest layer is at the top.

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The Cross-Cutting Law

• Any feature that cuts across a body of rock is
  younger than the body of sediment or rock it cuts
  across.

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The Law of Inclusions

• If one rock layer contains fragments (inclusions)
  of another rock layer, it must be younger than
  the fragments of rocks it contains.

Younger
Oldest
Youngest
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Oldest? Youngest?
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Oldest? Youngest?
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Oldest? Youngest?
D oldest at the bottom superposition law A
next to bottom superposition law B Tilt
plate tectonics Law of Horizontality E
intrusion cross-cutting law Erosion not
horizontal/straight line - Law of Horizontality C
intrusion Law of cross-cutting Erosion
Horizontality   DABEC (old to young)   E and C
are igneous (magma rising) A, B, D are
sedimentary (layers)
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Oldest? Youngest?
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Oldest? Youngest?