Question

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.

Answer 1

The ends of the geologic eras such as the Paleozoic and Mesozoic are marked by mass extinctions.

Hope this helps!

Answer 2

A. mass extinctions.

Step-by-step explanation:

Mass extinction refers to extinction of species on a big scale usually at the end of geological eras. It paves way for another era and new type of species composition is formed.

Paleozoic era ended with a mass extinction. This was the biggest mass extinction on history of earth and it wiped out 70% of land life and 95% of marine life. It paved way for Mesozoic era which was ruled by the dinosaurs. This era had Triassic, Jurassic and Cretaceous periods. It also ended with a mass extinction called as "The Great Extinction" and Cenozoic era began.