Answer:
An eon
Step-by-step explanation:
The first broad division of the geologic timescale is the eon. Others are Eras, Periods and Epoch.
Eons are the most broad and the largest of divisions of the timescale. There are two categories of the eons which are:
- Hadean eon
- Archean eon
- Proterozoic eon
- Phanerozoic eon
The Phanerozoic eon is the most recent. The Hadean eon is the is the oldest eon.