Geologic Time

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Geologic Time
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What is Geologic Time?
Geologic time is the history of the Earth from
its formation to the present

• It is broken up into 4 different ERAs
• Precambrian Era 4600 million to 570 million
  years ago
• (earliest life)
• Paleozoic Era - 570 to 245 million years ago
• (ancient life)
• Mesozoic Era - 245 to 66 million years ago
• (middle life)
• Cenozoic Era 66 million to present
• (recent life)

Each era represents a time of major sediment
deposition and plate movement
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To get a better understanding of Geologic time,
the 4 different eras and to discover what events
occurred in each era, complete the exercise on
page 119 of your textbook.
Cenozoic (1) -Rocky Mtns form -ice sheets cover
NA
Precambrian (88) -Shields formed -Canadian,
Brazilian, African and Australian
Paleozoic (7) -large parts of NA covered by
water -Appalachians formed
Mezoic (4) -water drops in NA -Innuitian mtns
form
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Breaking Up Each Era -each era is broken up into
periods, named for the area where the rocks from
the time period were first discovered
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How old is the Earth?
-Scientists cannot determine exactly how old the
Earth is
Why?
-They use rocks and Earths oldest rocks have
been destroyed or recycled by plate
tectonics -The oldest rocks (4 billion) ever
found were found in Canada near Great Slave Lake
How?
Radiometric Dating -measuring the half-lives of
long-lived radioactive isotopes naturally
occurring in rocks and minerals on the Earth
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So, how old is the Earth?
4.6 BILLION YEARS
Give or take a few million years