Curiosity has found seasonal occurrences of methane and some organic molecules on Mars. Both or possible indicators of carbon based life processes, but can have other non-biological explanations. Methane has been intermittently found previously on Mars. However, lacking a continuous long term record the seasonal variations were not obvious. The seasonal variation could be explained by either biological or non-biological processes. The organic molecules are from 5 cm below the surface in the Gale crater where they were shielded from UV irradiation (which would be expected to breakdown organic material). The Gale crater is an impact crater from 3.5 to 3.8 B years ago, that at some time was filed with water in which the sediments containing the organics were laid down. The organics were found in mudstones at the base of the craters' deposits. CNN article here. Open access Science methane article here. Open access Science organics article here.