Question

the cambrian explosion lead to the formation of many new groups of multi-cellular organisms from a single common ancestor and three geological eras. which is true about life on earth during this time?
a the permian-triassic era was known as the \age of the dinosaurs\.
b the mesozoic era began 252 million years ago and was known as \ancient life\.
c the cenozoic era began 66 million years ago and was known as the \age of mammals\.
d the paleozoic era spanned from 540 to 252 million years ago and was known as the \age of the reptiles\.

Explanation:

• Option A: The "age of the dinosaurs" is the Mesozoic era, not the Permian-Triassic (part of Paleozoic), so this is false.
• Option B: The Mesozoic era began 252 million years ago, but it is called the "age of reptiles/dinosaurs", not "ancient life" (that refers to Paleozoic), so this is false.
• Option C: The Cenozoic era started 66 million years ago after the dinosaur extinction, and it is widely known as the "age of mammals" as mammals became the dominant land life, so this is true.
• Option D: The Paleozoic era (540-252 million years ago) is called "ancient life", while the "age of reptiles" is the Mesozoic era, so this is false.

Answer:

C. The Cenozoic era began 66 million years ago and was known as the "age of mammals".