NASA's Mars Curiosity rover has measured a spike in methane in the atmosphere around it, and for the first time has definitively detected organic molecules in a rock-powder sample collected by the robotic laboratory's drill. The increase and decrease in methane means that present-day Mars is an active environment. Organic molecules are the building blocks of all known forms of terrestrial life, and consist of a wide variety of molecules made primarily of carbon, hydrogen, and oxygen atoms. However, organic molecules can also be made by chemical reactions that don't involve life, and there is not enough evidence to tell if the matter found by the team came from ancient Martian life or from a non-biological process. The organic molecules found by the team were in a sample of mudstone in Gale crater. Scientists think the crater was once the site of a lake billions of years ago, and rocks like mudstone formed from sediment in the lake. While the team can't conclude that there was life at Gale crater, the discovery shows that the ancient environment offered a supply of reduced organic molecules for use as building blocks for life and an energy source for life.