Question

sharp drops in the number of genera over a short period of time are seen at 66 million years ago and 252 million years ago, which indicate mass extinction events. the number of genera are relatively steady 75 million years ago and 400 million years ago, so no mass extinctions are observed at those times. discuss analyze the graph with a partner. how many mass extinctions did you identify? how did you determine when they occurred?

Explanation:

Step1: Identify mass - extinction events

Sharp drops in genera number indicate mass - extinctions. There are drops at 66 million years ago and 252 million years ago.

Step2: Count the number of events

There are 2 such drops, so 2 mass - extinction events.

Step3: Determine the occurrence time

The times are determined by the time points associated with the sharp drops, which are 66 million years ago and 252 million years ago.

Answer:

• Number of mass extinctions: 2
• Occurrence times: 66 million years ago and 252 million years ago