Related Clues:
- Its make-up is many years
- What a waiting time may seem
- Mighty long time
- Quite a spell
- One billion years, in astronomy
- Long stretches
- Group of eras
- Series of periods
- Vast time period
- Geologic division
- Longest division of geological time
- Forever, figuratively
- Time measured in ages
- Geologist's division
- Astronomical unit