Page 107 - Science Course 3 (Book 1)

Mo3-L1b: What is the Evidence for Evolution?

Extinction
event that occurs when the last individual organism
of a species dies.

Rate of Extinction
Number of extinct animals 100
1000

10

1
1800
1700
Biological Evolution 1900 2000
the change over time in populations of related
organisms.

Let’s Begin

Determining a Fossil’s Age
Scientists take
advantage of
radioactive decay,
a natural clock-like
process in rocks, to
learn a rock’s
absolute age, or
its age in years.

To measure the age of sedimentary rock layers,
scientists calculate the ages of igneous layers
above and below them.

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