Q: Answer the following question given this paragraph: Since life began on Earth, there have been several major mass extinctions. If you look closely at the geological time scale, you will find that at least five major mass extinctions have occurred in the past 540 million years. In each mass extinction, over 50% of animal species died. The total number of mass extinctions could be as high as 20. Q: What events, resulting in death of over half of animal species, have occurred on earth at least five times in the past 540 million years? A:

Choices:
[I] mass migrations;
[II] microevolutions;
[III] spontaneous mutations;
[IV] mass extinctions;
A:
[IV]