The graph below shows the extinction rates for families of marine organisms over different periods of Earth's history.What is the best estimate for the background extinction rate given these data?
A)14-20 families per million years
B)8-12 families per million years
C)2-5 families per million years
D)2-20 families per million years

Question

The graph below shows the extinction rates for families of marine organisms over different periods of Earth's history.What is the best estimate for the background extinction rate given these data? 
A)14-20 families per million years 
B)8-12 families per million years 
C)2-5 families per million years 
D)2-20 families per million years

Quizplus · Accepted Answer

The background extinction rate is the normal rate of extinction between mass extinction events. From the graph, it can be seen that the average extinction rate for families of marine organisms over the last 500 million years has been around 5 families per million years. However, the extinction rates during mass extinction events are much higher, which skews the average. Therefore, a better estimate for the background extinction rate would be the lower end of the range, which is 2-5 families per million years (Choice C).

The Graph Below Shows the Extinction Rates for Families of Marine