The oldest known piece of Earth? A 4.4 billion-year-old zircon
John Valley, University of Wisconsin-Madison
Until recently, many discounted the idea that life could have existed on Earth before 3.8 billion years ago because it was thought that heavy pummelling from asteroids would have made this impossible. But several lines of evidence are pointing to an earlier origin of life, and as we begin to question whether the late heavy bombardment really happened at all, it’s beginning to look like life started surprisingly early in our planet’s history.
The earliest fossil evidence – around 3.5 billion years ago
