What defines the boundaries between each of the three eras in the geologic timescale?
A) Two great mass extinctions
B) The age of the Earth divided by three
C) A decision by the Geological Society of America
D) Principles of relative dating

Question

Quizplus · Accepted Answer

Two great mass extinctions are significant events that define the boundaries between the three eras in the geologic timescale. These mass extinctions mark profound changes in Earth's biota, leading to the distinction between the Paleozoic, Mesozoic, and Cenozoic eras.

What Defines the Boundaries Between Each of the Three Eras