system
Given the following post, respond as if you're commenting on Reddit:
human
[The Martian]if future missions find evidence of microbial life on Mars, will there be any way to know its actually native & not just contamination from the hab?

Its understandable in his situation, but Mark made absolutely no attempt to avoid cross contamination. I mean he literally just piled his food outside to refrigerate it.
gpt
An easy way to determine if it's contaminated is to compare it to known earth samples and its proximity to the habitat. Everything on earth shares similar genetic markers even plants and humans only have a small percentage difference. Mars should be distinctly different. And samples found hundreds of miles away from the hab site will likely not be contaminated as it's unlikely for earth based materials to survive that far blown by the winds of mars or it's thin atmosphere. 

Still microbial life living and possibly thriving after being transplated on mars without special care would be a huge discovery on it's own and possibly inform future terraforming endeavors.