Related Clues:
- Geological time periods
- Near-infinite timespans
- Lengthy units of time
- With 37-Down, way back when
- Incalculable amounts of time
- Stellar periods
- Long, long periods
- Quite a long time
- How long it takes canyons to form
- G permits them all
- Ages and ages and ages
- Immeasurable time
- Gets old
- One billion years, geologically
- Grows more antiquated