Early Earth's Asteroid Rain Delayed Plate Tectonics
For most of human history, we imagined early Earth as a kind of cosmic shooting gallery where asteroids rained down, continents were impossible. Nothing could survive.
New work on early Earth's bombardment history confirms the constant pummeling was relentless. The field's consensus on what this meant for life's emergence has quietly been getting things backwards.
Researchers studying crater records and impact dynamics now have better models of how long this period actually lasted and what kind of crust could or couldn't form under sustained bombardment. The impacts were systematic enough, frequent enough, and energetic enough to prevent plate tectonics from getting started. No subduction, no continental accretion, no stable ground for roughly 500 million years.
Everyone in geology and astrobiology talks about this period as a barrier to habitability — too hot, too violent, unsuitable. We assume that reducing the asteroid rain would have been good news for life's prospects, faster habitability, earlier biogenesis, simpler path. But consider what happens on a young planet without sustained bombardment: you get plate tectonics earlier and stable continents sooner. Planetary chemistry doesn't work that way.
The assumption that early Earth was too hostile for life to begin may be exactly backwards—the hostility may have been what made life's chemistry possible in the first place.
”The data suggests that the asteroid bombardment wasn't just part of early Earth's history but may have been part of the chemistry that made life possible. And that a calmer early Earth would have been a worse one for abiogenesis to begin.
