The Geologic Time Scale

The entire history of the Earth can be divided into the Precambrian (ancient) Eon and the Phanerozoic (current) Eon. Which of the following correctly represents the percent of Earth's history occupied by each?

• 88% Precambrian, 12% Phanerozoic

• 12% Precambrian, 88% Phanerozoic

• 81% Precambrian, 19% Phanerozoic

• 19% Precambrian, 81% Phanerozoic

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Which segment of time is the smallest?

• Eon

• Era

• Period

• Epoch

Geologist divided the time between Precambrian Time and the present into three long units of time called _____________.

• eras

• periods

• epochs

• seconds

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The Triassic Period, the Jurassic Period, and the Cretaceous Period occurred in the ___________________ Era.

• Mesozoic

• Precambrian

• Cenozoic

• Instagram

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Names for many of the geologic periods come from __________.

• Places around the world where rocks of a specific age were found

• Famous People

• Unique characteristics found in the rocks of that period

• Famous Places

Scientists chose where units of geologic time began and ended based on major changes in ___________________ at certain times.

• life forms

• ocean levels

• weather patterns

• major geologic events

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These represent the greatest expanses of time on the geologic time scale.

• Geologic time scale

• Eons

• Phanerozoic

• Eras

• Paleozoic

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The eon that began 542 million years ago, a term that means visible life.

• Geologic time scale

• Eons

• Phanerozoic

• Eras

• Paleozoic

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Eons are divided into these smaller units:

• Geologic time scale

• Eons

• Phanerozoic

• Eras

• Paleozoic

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The earliest era within the Phanerozoic eon, meaning ancient life.

• Geologic time scale

• Eons

• Phanerozoic

• Eras

• Paleozoic

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