NASA's Curiosity rover has found some of the best evidence yet that ancient life may have existed on Mars — and an answer for what could have wiped it out.
When drilling into rocks on Mount Sharp, the central peak of the Red Planet's Gale Crater, the rover found evidence of siderite, an iron carbonate whose presence suggests Mars once had a carbon cycle. This hints that Mars once had potentially habitable conditions, and therefore possibly even life.
