The ends of the geologic eras such as the Paleozoic and Mesozoic are marked by
A.
mass extinctions.
B.
index fossils.
C.
radioactive decay.
D.
climate changes.
The ends of the geologic eras such as the Paleozoic and Mesozoic are marked by "climate changes" since these changes brought about devastating effects on the climate, which was crucial for the survival of many animals and plant life.
