We’ve been expecting aliens from Mars for decades now, but what if life was vanquished on the red planet before evolution ever got the chance to take hold?

A pair of researchers recently published an analysis of 3.5 billion-years-old soil samples from Mars containing chemical compounds called “thiophenes” that could, potentially, be organic. If they are, it would be highly likely that bacteria once lived on the planet.

Terrestrial thiophenes are considered tell-tale signs of life by Earthbound biologists. The presence of these possibly-organic compounds in Martian soil represents the strongest evidence yet that life may have once existed anywhere other than Earth.