Page 131 - Science Course 3 (Book 2)

Mo11-L4b: What Causes Mass Extinction?

geographic isolation Evidence for this impact is in a clay layer containing
the element iridium in rocks around the world.
the separation of a population of organisms from
the rest of its species due to some physical barrier,
such as a mountain range or ocean.

Let’s Begin Iridium Anomalies

Key Concept
Responses to Change What Causes Mass Extinction?

A mass extinction is the extinction of many species Describe a possible event that could cause a mass
on Earth within a short period of time. extinction.

There have been several mass extinction events in
Earth’s history.

Extinction Events
3,000

2,500
Number of genera 2,000

1,500

1,000

500
Evolution is the change in species over time as
0 organisms adapt to their environments.
Camb. Ord. Sil. Dev. Carb. Perm. Tri. Jur. Cret. Tert. Sudden, catastrophic changes in the environment

Period and the slow movement of Earth’s tectonic plates can
both affect evolution.
If the environment changes quickly and organisms
cannot adapt to the change, they die.

Scientists hypothesize that a meteorite impact might
have caused the mass extinction that occurred when
dinosaurs became extinct.

Eohippus
Pliohippus
Mesohippus
Merychippus
Modern Horse
A land bridge connects two continents that were
previously separated.
Over time, organisms move across land bridges
and evolve as they adapt to new environments.
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