If there is life on Mars, we might have given it a lift from Earth to Mars on robotic scouts which are ironically looking for life and its conditions.
Scientists every day hypothesize on what forms of life might have evolved on other planets setting Earth’s wide spectrum of life as the example. However what many tabloids forget to mention is that life already exists outside Earth. It exists on Mars. Questionable, costly sterilization techniques, and policies may in fact be a cause of transfer of life that is alien to Mars.
Earth’s microbes could be terraforming Mars already. One microbe could have dropped into the planets surface and waited for the right time to spring to life. Detecting large but steady blooms of methane gas, in equatorial regions, on Mars’ warmer months, could be coming from a trillionth generation of that one (maybe more) microbial stowaways.
A microbe if in an unfavorable or starved condition can do any number of things, sporulate (become dormant), become competent (absorb local genetic material, maybe even of non-nucleic acid form)