Related Clues:
- It's split into eras
- Quite a long time
- It's longer than an era
- Big time division
- Span of epoch proportions?
- Extensive period
- Immeasurable time
- Billion-year time period
- One billion years, geologically
- Humongous span
- Annoying wait, facetiously
- Untold eras
- Inconceivable stretch
- Very long interval
- Long while