Page 132 - Science Course 3 (Book 2)

Mo11-L4b: What Causes Mass Extinction?

Geographic isolation is the separation of a popula- Precambrian Time
tion of organisms from the rest of its species due to
some physical barrier, such as a mountain range or Time before the Cambrian is called Precambrian
an ocean. time.
Separated populations evolve in different ways as Scientists have determined that Precambrian time is
they adapt to different environments. nearly 90 percent of Earth’s history.

Porkf sh
(Anisotremus Virginicus)

The rare fossils of multicellular life-forms in Precam-
brian rocks are from soft-bodied organisms different
Isthmus of Panama from organisms on Earth today.
arose 3.5 million
years ago Many of these organisms became extinct at the end
of the Precambrian.

Panama Porkf sh
(Anisotremus Taeniatus) Precambrian life led to new multi-celled organisms in
the Cambrian period.

This sudden appearance of new, complex life-forms
Key Concept is called the Cambrian explosion.
What Causes Mass Extinction?

How can geographic isolation affect evolution?

SUMMARY

What Causes Mass Extinction?
Climate change caused by the results of a
meteorite impact could contribute to a mass
extinction event.

Slow changes in geography affect evolution.

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