Exploratour: Life on Mars?
Mars in the Past
In the past, Mars was much different than it is today. Liquid water used to flow on the surface. 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 lots of air in place to keep the surface warm. (This effect is called the "greenhouse effect"). In this environment life may have once existed.
It's not likely that Mars will go back to being friendly to life. So any life that would come to exist would probably be different than life we know about!