Related Clues:
- A billion years, in geology
- "___ Flux"
- A very, very long time (Var.)
- A billion years, to geologists
- Many generations
- Immeasurably long period of time (Var.)
- Umpteen millennia
- Mind-boggling time span
- Reeeeeeally long time
- Very long time (Var.)
- Longest division of geologicalà time
- Gigayear
- Forever and a day, facetiously
- It's a real stretch
- Astronomically long time