DID comets made mainly of water ice launch an assault on the young Earth and its fledgling moon?
The two worlds were battered by debris about 3.85 billion years ago, during the so-called Late Heavy Bombardment (LHB), but it is unclear whether rocky asteroids or icy comets were the key culprits.
Uffe GrÃ¥e Jørgensen at the in Copenhagen, Denmark, and colleagues reasoned that the element iridium could provide a clue. Comets and asteroids both contain iridium, but comets would leave less iridium on the Earth and hardly any on the moon, compared with asteroids,…
