Thin CO 2 atmosphere. Life stored CO 2 . Thus recycle CO 2 from buried carbonate rocks May have happened in the past on Mars, but not recently 5. Tides will overwhelm self-gravity and tear apart a moon inside the Roche Limit. Or tides will prevent a moon from forming inside this distance Almost all rings are inside the Roche limit.
Comet orbits suggest a huge reservoir of objects far away.
However, they could not have formed there, wasn't enough material out there. Comets and water-bearing asteroids may have been early sources of water and building blocks of life . Major extinction of life 65 million years ago. Iridium is much more abundant in iron meteorites. Life began 3.8 billion years ago.