The Precambrian Earth

1
Chapter 22

• The Precambrian Earth

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Precambrian Time -includes everything before the
________ period of the Paleozoic era -length of
about ___ billion years -88 of earths
history -much historical evidence destroyed
Cambrian
4
3
Barringer Crater

• How did this feature form?

Impact from meteor
Do you think events like this were more or less
common?
more
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Crust Formation

• Differentiation
• -_______ materials sink toward center and _______
  materials accumulate near surface

heavier
lighter
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Precambrian _______ core of Archean and
Proterozoic rocks ________ rocks in North
America make up craton
Shield
oldest
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_________ ancient continent _____ billion
years ago
Laurentia
1.8
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Rodinia
_________ first _______________ ______million
years ago
supercontinent
750
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Precambrian Atmosphere

• Volcanic Outgassing
• -produced atmosphere of _____________, carbon
  dioxide, nitrogen, and carbon monoxide, but not
  __________

water vapor
oxygen
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Oxygen Producers

• Stromatolites
• -large mats of ________________
• -dominated shallow __________ of Proterozoic
• -nearly identical to those found in ___________
  today

cynobacteria
oceans
Australia
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Oxygen Evidence

• Banded Iron Formations
• -alternating layers of _________ and
  _______________
• -result of locally high __________ levels in
  early Proterozoic

chert
iron oxides
oxygen
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Early Life
_____________ single cell organism no
nucleusonly life before Proterozoic includes
cynobacteria
Prokaryote
Eucaryote
__________ contains nucleus larger
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Edicara Fauna
__________ shallow marine organisms of 670 to
570 million years ago extinct before_________
era begins
Paleozoic
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Chapter 22 Review

• What is the commonly accepted age of the Earth?
• What is the process by which a planet becomes
  internally zoned?
• What is the name of the first supercontinent that
  formed near the end of the Proterozoic?

4.6 billion years
differentiation
Rodinia
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Chapter 22 Review (continued)

• 4. Describe the major difference between Earths
  early atmosphere and explain how this occurred.
• 5. Describe the difference between prokaryotes
  and eukaryotes and tell which is older.

Todays atmosphere contains oxygen given off by
photosynthetic plants.
Prokaryotes are smaller, have no nucleus, are
less complex, and came first.