Planet-sterilizing asteroids struck Earth until around 4.3 billion years ago
Space rocks larger in diameter than Utah bombarded the early Earth, probably repeatedly eradicating emerging life on the planet's surface. The last of these death rocks struck around 4.3 billion years ago, scientists estimate in the July 31 Nature, providing an upper limit to when life first took hold on Earth.
From Earth’s origin around 4.6 billion years ago until 3.8 billion years ago, the planet was such a hellish place that geologists call this eon the Hadean after Hades, the Greek god of the underworld. Debris left over from the solar system’s creation regularly slammed into Earth, boiling away the early ocean and coating the planet with molten rock.
But it was during this chaotic period that scientists think life arose on Earth.
“If life on Earth emerged before [a] final sterilizing impact, it may have been completely erased,” says planetary scientist and lead author