Actually, that’s the real title of the article, too. National Geographic tells it like it is, baby.
My two main thoughts upon reading this:
1) So wait, we may be able to find evidence that life once existed on Mars by hunting down ancient lava tubes and scouring them for poo?
2) I bet our microbial poop is TOTALLY prettier than that substandard Martian microbial poop. Suck it, Mars.