Question

Which period makes up nearly all of the Cenozoic era?

Answer 1

The Paleogene was the longest period of the Cenozoic Era,

Explanation:

Here's a video that illustrates the periods of the Cenozoic,
using this graphic:

http://study.com/academy/lesson/the-cenozoic-era-definition-time-period-facts.html
(around 0:20)

You can find out more about the Cenozoic Era and the Paleogene Period at this Live Science site:
https://www.livescience.com/40352-cenozoic-era.html