Actually there is
evidence on Earth that there was life on Mars at some point, in form of microscopic fossils that came in a
meteorite.
And the features above ground clearly indicate ancient bodies of fluid (ie. water), that probably evaporated long ago when the planet lost most of its atmosphere. Mars very likely had all the conditions to sustain microbial life billions of years ago. Some people argue that actually life on Earth could have come from Mars, not the other way around...
This is the kind of thing that gets rumors about life on Mars started.
First, they don't know that the meteor is from Mars. Wikipedia states this:
Like other members of the group of SNCs (shergottite, nakhlite, chassignite), ALH84001 is thought to be from Mars. However, it does not fit into any of the previously discovered SNC groups.
Second, Bacteria claims have been rejected by "the wider scientific community:"
These claims were controversial from the beginning, and the wider scientific community ultimately rejected the hypothesis once all the unusual features in the meteorite had been explained without requiring life to be present. Despite there being no convincing evidence of Martian life, the initial paper and scientific and public attention caused by it are considered to be turning points in the history of the developing science of astrobiology.
