Law of Superposition

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Law of Superposition
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Law of Superposition

• In horizontal rock layers the oldest layer is at
  the bottom and the youngest layer is at the top
• This is called Relative Dating

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Age

• Relative agerocks compared, no dates older
  rocks, younger rocks
• Absolute agerocks have a chronologic age
  assigned. 330 million yrs old,2.5 billion yrs old

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Unconformity

• Gap in the geologic record
• Igneous rock formations
• Faults (breaks in rock)
• Missing rock layers

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Igneous rocks

• Extrusionlayer of igneous rock form from lava on
  the surface of the earth
• Intrusionlayer of igneous rock that pushes from
  inside the earth, formed from magma
• Igneous layers are always younger than rocks
  beneath them or the rocks they intrude through

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• Index fossilfossil that helps to date a rock.
  Fossil had to have been widespread and lived only
  a short time period

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Radioactive Dating

• During radioactive decay, the atoms of one
  element break down to form atoms of another
  element

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• To find the age, scientists compare the ratio of
  the parent element to the daughter element
  that are found in the rock sample, then compare
  that to the half life of the element

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• http//www.colorado.edu/physics/2000/isotopes/radi
  oactive_decay3.html
• Half lifeamount of time it takes for the ½ of
  the parent to decay to the daughter

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