Mars in the Past
In the past, Mars was much different than it is today. Liquid water used to flow on the surface, as shown in this picture. Both the Earth and Mars should have been frozen in their early history because the sun was weak at first, but both planets show that water was flowing, which suggests that they both must have had thick atmospheres in place to keep the surface warm. In this environment life may have once existed.
The atmospheres on both planets came out of volcanoes. There were not many volcanoes on Mars, and those volcanoes were never very active. Compare this to the Earth where volcanism continues today.
The volcanic eruptions produce a lot of water. The water eventually falls to the ground or into the oceans. Mars is small, and so cooled off very rapidly. Mars was sufficiently cold for water to be absorbed into the ground and freeze like tundra in the Canadian northwest. Today scientists estimate that a large amount of water is frozen into the surface of Mars. They estimate this happened by 2.8 billion years ago.
So it is not likely that Mars will become a haven for life in the future...unless it is life unlike that which we know?