Download Geologic Time Scale

Geologic Time Scale
The History of Our Earth
Geologic Time Scale
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Used to show Earth’s history because
the time span is so great.
It is a record of life forms and
geologic events in the Earth’s history
Created by studying rock layers and
index fossils.
Divisions in the scale depend on
large events in history, such as mass
extinctions.
Geologic Time Scale
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Record of
Geologic events
Eras are divided
by major mass
extinctions
Periods further
divide time in
tens of millions
of years
How do Geologists use fossils
to determine time?
 Index
Fossils: Fossils with a wide
geographic distribution and a limited
time span.
 Used to determine relative age.
550 Mya
245 Mya
Fossil Correlation
 Using
several fossils in combination
to pinpoint the approximate relative
time that a certain layer of rocks was
formed.