Geologic History

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Geologic History

• Created By
• Mr. Kreeger

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HW and Page References

• Page References-Chapter 32 (pages 597-609)
• Homework
• 1-3 on page 599
• 4-8 on page 605
• 11-14 on page 609

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Table of Contents

• How to determine Geologic record of life on
  earth.
• Evidence from rocks
• Relative Age/ Absolute Age
• Relative Age/The duh Laws
• Igneous Intrusion
• Law of Cross cutting
• Law of included fragments
• Unconformity
• Sequence of events

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1. How to determine the Geologic record of life
on earth.

• Evidence From Rocks
• By looking at rocks and the materials they
  contain, can infer age of them.
• Looking at patterns in rock layers and location
  of fossils allow inferences about relative age of
  rocks and events that shaped them

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1. How to determine the Geologic record of life
on earth.

• Relative Age/ Absolute Age
• Relative Age-Determining the rocks age as
  compared to the age of the other objects of known
  ages.
• Absolute Age-Determining the actual age of rock
  by using ideas associated with radioactive decay.

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2. Relative Age/ The Duh laws!!

• SUPERPOSITION sedimentary sequence will be
  OLDEST on BOTTOM (if undisturbed)
• ORIGINAL HORIZONTALITY sediments are deposited
  horizontally. Tilting Folding happens AFTER.
• LATERAL CONTINUITY sediments are deposited in
  continuous layers.
• CROSS-CUTTING - a body of igneous rock is younger
  than rock it has intruded (cut across)
• INCLUDED FRAGMENTS - pieces of rock found IN
  another rock must be OLDER (formed first)

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YOUNGEST TO OLDEST
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Igneous Intrusion
occurs when magma squeezes into or between layers
of pre-existing rock
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LAW OF CROSS-CUTTING
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LAW OF INCLUDED FRAGMENTS
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UNCOMFORMITY

• A buried surface of erosion separating two rock
  masses
• Represents a gap in geologic time

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.a look at the Grand Canyon and 3 types of
unconformities...
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1
3
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Angular Unconformity- An unconformity in which
the beds below the unconformity dip at a
different angle than the beds above it.
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DISCONFORMITY

• An unconformity in which the beds above the
  unconformity are parallel to the beds below the
  unconformity, though layers are missing.

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SEQUENCE of events

1. The land surface subsided (or the water level
   raised), submerging the erosion surface
2. A new series of sediments deposited in horizontal
   layers on the erosion surface
3. The complicated sequence of tilted and horizontal
   rocks was again uplifted, exposing them to
   erosion and producing the outcrop we see today

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STEP 3
STEPS 4-6
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Practice What Happened Here?
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PLAY THE WHICH CAME FIRST GAME!  1). D or
L?  2.) M or C?  3.) N or E?  4.) B or
A?  5.) I or Q?  6.) Q or J?  7.) M or A?
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4. Absolute Age

• This is the true age of the earth that is based
  on radioactive decay certain elements.
• Radioactive decay- Atoms of unstable isotopes
  break apart, energy is given off when this
  occurs-New stable elements are formed called
  decay product
• Half Life- The amount of time it takes the
  material to decay to half of its original.

Earth Science Reference Tables-Handout
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In class problems

• A rock contains 6.25 grams of Potassium-40 and
  93.75 grams of Argon-40. How old is the rock
• A rock is determined to be 22,800 years old. If
  the rock had 100 grams of Carbon 14 22,800 years
  ago, how many grams of Nitrogen-14 and Carbon-14
  are present now?
• Which radioactive isotope would you use to find a
  rock that is
• 10 million to 4.6 billion
• 50,000 to 4.6 billion
• 100-70,000