Men are from Mars...

...and women and bacteria too.

Early Earth had some disadvantages as a place for life to start.  For one thing, there was little if any land - perhaps a few volcanoes poking up here and there, and water does not like nucleic acids like RNA.

Mars, on the other hand, had several things Earth lacked, as well as things Earth had, like water.  In particular it had deserts and ice caps, both of which Earth lacked.  For that reason, there is a significant number of origin of life partisans who think that life started on Mars and then got transferred to Earth.

It turns out that Earth does have a lot of stuff we got from Mars - a billion tons or so.  Asteroid impacts on Mars blast a bunch of Mars out into the solar system, and some of it makes its way to Earth.  Simulations show that bacterial spores could potentially survive the trip.

These considerations are one reason that the search for traces of ancient life on Mars are taken seriously.


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