billion years
Deep time unit
A billion years is a unit of deep time used in geology, astronomy, and evolutionary biology.
The Earth is about 4.5 billion years old; the universe, roughly 14 billion.
The phrase appears in discussions of planetary formation, species evolution, and cosmic timescales: Life emerged on Earth about 3.8 billion years ago.
In casual use, billion years can be hyperbolic: It's been a billion years since we talked.
- eonsImmense spans of time
- cosmicPertaining to the universe
- Big BangUniverse's explosive origin
- ancientVery old indeed
- primordialExisting from the start
primordial soup · dawn of time · geologic · deep time · geological ages · epoch · abyss · eternity · prehistoric · timescale · universe · formation · evolution · stars · galaxies · dinosaurs · mass extinction · fossils
billion yearsinstant
Briefest unit of time
nanosecond · split second · microsecond · moment · millisecond
billion yearsrecorded history
Past preserved through documentation
here and now · today · now
billion yearslifespan
Total existence duration
generation · recorded history · career · era
billion, billions, billionth, billionaire, billionaires, year, years, yearly, yearling