Isotopic composition of Martian meteorites showed that 4.5 billion years ago, the Red Planet was subjected to intense asteroid bombardment. It brought so much water that for a short time Mars was much more suitable for the origin of life than neighboring Earth.
According to some scientists, young Mars could have been the place where the first life in the Solar System appeared. Estimates suggest that there was indeed a lot of this water. Together with the "primordial" water ejected from the magma, the moisture was enough to cover the young Mars with a global ocean at least 300 meters deep, and possibly up to a kilometer.