Introducing Earth

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Introducing Earth
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Chapter Nine Earth and Time

• 9.1 Relative Dating
• 9.2 Geologic Time

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9.1 The beginnings of geology

• In 1666, Nicholas Steno, a Danish anatomist,
  studied a sharks head and noticed that the
  sharks teeth resembled mysterious stones called
  tonguestones.

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9.1 Evidence from Rock

• Steno theorized that tonguestones looked like
  sharks teeth because they actually were sharks
  teeth that had been buried and became fossils.

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9.1 What is relative dating?

• Stenos principles are used by geologists to
  determine the age of fossils and rocks in a
  process called relative dating.
• Relative dating is a method of sequencing events
  in the order they happened.

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9.1 What is relative dating?

• James Hutton (17261797) showed how processes
  today might explain what happened a long time
  ago.
• For example, grooves left behind by flowing
  rainwater helped explain the formation of the
  Grand Canyon from the Colorado River.

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9.1 Superposition

• Stenos ideas for relative dating include
  superposition, original horizontality, and
  lateral continuity.
• Superposition states that the bottom layer of
  sedimentary rock is older than the layer on top
  because the bottom layer formed first.

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Rock layers may bend or shift and are found
standing vertically, or tilted, or rolled into
curves.
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9.1 Lateral continuity

• Horizontal layers of rock are continuous.
• By comparing rock layers in the Grand Canyon,
  geologists have found that the layers on one side
  of the canyon match up with the layers on the
  other side.

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9.1 More relative dating

• The idea of cross-cutting relationships states
  that a vein of rock that cuts across a rocks
  layers is younger than the layers.
• The middle and top layers formed after the bottom
  layer but before the vein.

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9.1 Faunal succession

• Faunal succession means that fossils can be used
  to identify the relative age of the layers of a
  rock formation.
• The organisms found in the top layers appeared
  after the organisms found in the layers below
  them.

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9.1 Fossils and Earths changing surface

• Most of the land on Earth was part of a large
  landmass called Pangaea about 250 millions of
  years ago.

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9.1 Fossils and Earths changing surface

• Fossils provide evidence for how Earths surface
  has changed over time.
• Scientists map fossil locations.
• Understanding Earths past helps explain how
  similar plants and animals ended up in different
  locations.

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