How many years old is the Earth?

How to get close to this number

Anchor on the universe. The universe is around thirteen and a half billion years old and the Earth formed in the later part of that history, so the planet has to be a few billion — roughly a third of the age of everything.

The dating method is the interesting part: the age comes from meteorites and the oldest terrestrial minerals rather than from rocks at the surface, because plate tectonics recycles the crust and destroys the oldest evidence. We date the Earth using material that never became part of it.

The timeline in the explanation is the framing worth keeping: life appeared within the first billion years, complex animals only in the last six hundred million, and humans in the final fraction of a percent. Compressing four and a half billion years into a proportional timeline puts all of human existence in the last few seconds of a year-long clock.