Geology

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Geology

• 10.09.07 / 10.10.07

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Essential Question

• How have the geologic sciences developed over
  time?

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Catastrophism

• Archbishop James Ussher developed a chronology of
  the world in the mid-1600s
• Calculated creation of Earth to have occurred Oct
  23, 4004 BC
• Chronology eventually printed in notes of many
  Bibles
• Led to principle of catastrophism

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Catastrophism

• Earth shaped by major disasters that no longer
  occurred.
• Noahs Flood for example
• Allows Earth to be quite young because its
  landforms can change quickly

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Modern Geology

• In late 1600s, Nicolas Steno developed
• Principle of original horizontality
• Law of superposition

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Modern Geology

• James Hutton wrote Theory of the Earth in 1785.
• Offered principle of uniformitarianism.
• Claims the same physical processes that occur
  today occurred in the past
• Understanding the present is the key to
  understanding the past

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Modern Geology

• Hutton wrote, We have a chain of facts that
  clearly demonstrates that the materials of wasted
  mountains have traveled through rivers.
• Claimed only long periods of time were required
  to shape the Earth as we see it.
• Modern geologists have calculated American
  mountains erode at 3cm/year.
• At that rate, a 10,000 ft mountain would erode in
  100 million years.

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It just takes time
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Modern Geology

• In 1821, Louis Agassiz heard another scientist
  claim there was evidence for glaciers in places
  where there were currently no glaciers.
• He attempted to disprove hypothesis.
• He ended up accepting hypothesis and forming a
  hypothesis of a great ice age.
• Provided evidence for uniformitarianism.

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Glacial valley
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Geology at work today

• Geologists impact our world in numerous ways
• Engineering geologist help design buildings to
  withstand earthquakes and other forces
• Petroleum geologists help find oil and natural
  gas
• Geology is also an essential part of astronomy,
  oceanography, paleontology, meteorology and more

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Check-up

• What is catastrophism?
• What is uniformitarianism?

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Essential Question

• How can scientists determine ages of geologic
  material?

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Relative dating

• Placing material and events in sequence
• Principles and rules of
• Law of superposition oldest rocks are on the
  bottom
• Principle of original horizontality sediment is
  deposited horizontally
• Principle of cross-cutting relationships
  younger feature cuts through an older feature

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Superposition is well illustrated by the strata
in the Grand Canyon
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Horizontality

• Principle of original horizontality claims layers
  of sediment are deposited horizontally.
• So, layers that are folded or otherwise distorted
  were distorted after they were deposited.

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Cross-cutting relationships
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Relative dating

• Unconformities
• An unconformity is a break in the rock record
• Types of unconformities
• Angular unconformity tilted rocks are overlain
  by flat-lying rocks
• Disconformity strata on either side are
  parallel
• Nonconformity igneous or metamorphic rock
  uplifted, eroded and then covered by sediment

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Formation of an angular unconformity
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Relative dating

• Principles and rules of
• Unconformities
• Types of unconformities
• Nonconformity
• Metamorphic or igneous rocks below
• Younger sedimentary rocks above

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Several unconformities are present in the Grand
Canyon
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Correlation of rock layers

• Correlation means to show a relationship
• Matching rocks of similar age in different
  regions
• Often relies upon fossils

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Check-up

• What is the difference between catastrophism and
  uniformitarianism?
• Do people who believe in catastrophism disagree
  with the law of superposition?