When did the Cenozoic era begin?

When did the Cenozoic era begin?

• A. Began 65.5 Ma and continues to present.
• B. Began 100 Ma.
• C. Ended 2 Ma.
• D. Began 500 Ma.

Answer: (A)

The moment the Cenozoic begins is tied to a major turning point in Earth's history: the end of the dinosaurs and the start of a new era about 65.5 million years ago, right after the Cretaceous–Paleogene extinction event. Since then, the Cenozoic has continued to the present and includes the Paleogene, Neogene, and Quaternary periods. That timing—around 65.5 million years ago and ongoing—is what makes this the correct start point. The other dates push the start into the wrong times (100 million years ago is still in the Cretaceous, 2 million years ago is far later than the beginning, and 500 million years ago is well before the rise of mammals and the Cenozoic).

The moment the Cenozoic begins is tied to a major turning point in Earth's history: the end of the dinosaurs and the start of a new era about 65.5 million years ago, right after the Cretaceous–Paleogene extinction event. Since then, the Cenozoic has continued to the present and includes the Paleogene, Neogene, and Quaternary periods. That timing—around 65.5 million years ago and ongoing—is what makes this the correct start point. The other dates push the start into the wrong times (100 million years ago is still in the Cretaceous, 2 million years ago is far later than the beginning, and 500 million years ago is well before the rise of mammals and the Cenozoic).