Earth History

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Earth History

• The Earth is 4.6 billion years old and its
  geology has changed greatly with time. Many of
  the changes in the past can be observed in the
  rock record. Interpreting the changes in the
  geology of the earth is similar to solving a
  puzzle we must figure out how all the pieces fit
  together.
• What events can change the geology of an area?

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Earth History

• Principle of Uniformitarianism the present is
  the key to the pastin other words, the
  processes that can change the geology today have
  worked on the rocks in the past in a similar
  manner.
•  
• Example Weathering breaks down limestone at the
  same rate today as it did thousands of years ago.
  (Weathering rate has not changed)

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Earth History

• Absolute Age the actual age of a rock or event
  (can be determined by radioactive decay of
  specific elements)
•  Some elements decay into other elements over a
  specific amount of time (half-life).

ESRT p.1
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Practice

• A sample with an original amount of 40g of
  carbon-14 is found and now contains 2.5g of
  carbon-14, how many years old is this sample?
• 40g 20g 10g 5g 2.5g
• This sample has undergone 4 half-lives, and the
  half-life of carbon-14 is 5700 years
• 5700 yrs. x 4 22,800 years!

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Earth History

• Relative age The age of rocks or events in
  relation to the age of some other rocks or
  events. (following a sequence of events)

A
B
D
C
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Earth History

• Using Sedimentary Layers to determine relative
  age
• Principle of original horizontality
• Principle of superposition
• Igneous Intrusions
• Faults and Folds

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Earth History

• Principle of original horizontality sediments
  are deposited in horizontal layers that are
  parallel to the surface on which they are
  deposited.
•  
• What does this tell us about tilted or folded
  layers of rock?

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Earth History

• Principle of superposition in a series of
  undisturbed layers, the oldest layer is on the
  bottom and each layer above is younger and
  younger.

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Earth History

• Igneous Intrusions Molten magma forces its way
  into cracks in rocks and hardens (forming an
  intrusion). Since the rocks through which the
  magma moved existed before the intrusion, these
  rocks must be older than the intrusion.
  (Intrusions are younger!)

Igneous intrusion
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Earth History

• Faults and Folds These features must be younger
  than the rock in which they are found.

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Unconformity
unconformity

• Erosion wears away rock layers, then more
  deposition occurs creating new layer. The
  unconformity is the old buried erosional surface.
  This is also known as a gap in the rock record.

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Put the events in order of oldest to youngest

1. _________________
2. _________________
3. _________________
4. _________________
5. _________________

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Put the events in order of oldest to youngest

1. _________________
2. _________________
3. _________________
4. _________________
5. _________________
6. _________________
7. _________________
8. _________________
9. _________________

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Put the events in order of oldest to youngest

• _________________
• _________________
• _________________
• _________________
• _________________
• _________________
• _________________
• _________________
• _________________

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Putting the sequence together?

• Correlation the process of matching rocks and
  geologic events in one location with rocks and
  geologic events in other locations.

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ESRT page 8-9
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ESRT page 8-9

• Time Scales
• Eon Era Period Epoch
• Largest Smallest

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ESRT page 8-9

• What can we find on this page?

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ESRT page 3
20
ESRT page 2
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Fossil Record

• Evidence of organisms preserved in the
  sedimentary rock record.
• Typically hard shelled organisms or bones of
  other organisms are the only evidence preserved
  as fossils.
• Organisms must be buried quickly after they die
  to be preserved.

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Index Fossils

• Used to locate a specific geologic period of
  time.
• Abundant and found over large geographic regions.
• Species lived for a short period of time.
• From ESRT page 8-9, identify an index fossil and
  the geologic time period it represents.