I wonder if having the Moon was the critical factor for the Earth.<p>The Moon's gravitational pull stirs the core of the planet and evens out the pull of the oceans across the planet. Maybe it's this stability that matters in the creation of long term water and stability.<p>By way of comparison, Venus, a planet similar to Earth without a comparable moon has a surface and atmosphere like living hell.
When Mars was a young planet, it was bombarded by icy asteroids that delivered water and organic chemistry necessary for life to emerge. According to the professor behind a new study, this means that the first life in our solar system may have been on Mars.