Related Clues:
- An age in school? Time to escape!
- Proterozoic, e.g
- They're much longer than 35-Across
- It totals 1 billion years
- Vast periods
- Vast time stretches
- Unimaginable span
- The Proterozoic, e.g
- So very long
- Impossibly long stretch
- Largest geologic time unit
- Impossibly long stretches
- Long time spans
- Extended stretch?
- Massive stretches of time