The Relative Age of Rocks

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The Relative Age of Rocks
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Law of Superposition

• In horizontal sedimentary rock layers, the
  oldest layer is at the bottom. Each higher layer
  is younger than the layers below it.

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Extrusion

• When lava hardens on the surface. It is always
  younger than the rock below it.

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Intrusion

• A mass of igneous rock below the surface is
  called an Intrusion. It is always younger than
  the rock layers around and beneath it.

5
Fault

• A fault is a break in the Earths crust. A fault
  is always younger than the rock it cuts through.
  It makes the layers not line up.

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Unconformity

• The surface where new rock layers meet a much
  older rock surface beneath them is called an
  unconformity. It is a gap in the geologic
  record.

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Index Fossils

• Index Fossils help match rock layers.
• Must be widely distributed and represent a type
  of organism that existed only briefly.
• They tell the relative ages of the rock layers
  in which they occur.

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Radioactive Dating

• When the atoms of one element break down to form
  atoms of another element.

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Carbon 14 Dating
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Half Life

• The amount of time it takes for half of the
  radioactive atoms to decay.

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Examples of Radioactive Changes in Rock

• Carbon 14
• - 5,730 years changes to Nitrogen
• Potassium 40
• 1,3 billion years changes to Argon
• Uranium 238
• 5.5 billion years changes to Lead

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The End!