The largest formal unit of geologic time is the eon. They are so long that they are divided into ages
The correct answer is Eons.
The largest formal unit of geologic time is an Eon.
An Eon is a very long period of time for which we cannot know exactly how many years it represents.
For geology, the Eon represents a period of a billion years, but also, it is each one of the periods in which the geological time of our planet is divided.
Therefore we have the following Eons:
-Phanerozoic: 543 million years ago.
-Proterozoic : from 2,500 to 543 million years ago
- Archaic: from 3,800 to 2,500 million years ago.