I’ve actually worked in astrobiology research :) I would point you towards the research that went into ALH-84001. Even if you don’t buy that it was an example

I’ve actually worked in astrobiology research :) I would point you towards the research that went into ALH-84001. Even if you don’t buy that it was an example of fossilized Martian life, analysis of the thermal stresses it suffered from ejection from Mars, time in flight, to impact on Earth showed conclusively that it was survivable. Had it been the other way around (Earth to Mars) it would have seeded Mars with life. We’ve shown that rock which could be carrying microbes can and has been exchanged between earth and Mars. Lots of such specimens land each and every year. You can quibble that we haven’t found actual life yet, but (1) lots of people think that’s exactly what ALH-84001 was. (2) we don’t have that many samples of Martian meteorites. We know lots of it falls every year, but most is either not found/collected/identified or contaminated on impact. (3) Mars meteorites falling now, ejected from a dry and sterile surface, would not be representative of what was falling in the early earth that was thrown from a wet, habitable Mars. To be clear, from an astrobiology perspective a negative result from the search for life on (or from) Mars is harder to explain than finding it. Both panspermia and second abiogenesis are simpler explanations.