Related Clues:
- One billion years, geologically
- A seeming eternity
- Some collars and jackets
- Becomes inattentive, with ''out''
- Billion-year increments, in geology
- Pays no attention, with ''out''
- Long, long times
- Hundreds of centuries
- Old postal divisions
- Mammoth time units
- Nigh-infinite periods
- Extremely long time periods
- Many lifetimes
- Geologic stretches
- Geologic time spans