"not clear why", by which I guess the implied ask is how it got there, which is likely because the universe has a bunch of carbon in it, and a whole other bunch of ways of distributing it, while also making and remaking it via a couple of other processes that the universe has running,<p>but the real ask, is the martain carbon concentrations derived from life, like the very random rock my left shoulder is leaning on, with whit patches, speckled with black dots, not counting the lichens, clearly also making the rock there home.
and that answer will probable come from someone going to mars and doing a few simple tests.
Mars ho!