The heavy bombardment
Asteroids batter the inner Solar System for hundreds of millions of years, scarring every surface.
- When
- —
- Duration
- 700 million years
- Known to
- ± 100 million years
- Era
- Hadean
The Moon's great impact basins record an era of intense bombardment. It was long read as a sudden cataclysm around 3.9 billion years ago, triggered by the outer planets migrating; that interpretation has weakened considerably. Apollo samples, lunar meteorites and high-resolution orbital data now favour a prolonged decline running from roughly 4.2 to 3.5 billion years rather than a narrow spike. Either way, Earth received the same battering — its record has simply been erased.