The Sample Analysis at Mars (SAM) instrument on Curiosity found evidence for biologically useful nitrogen in the Rocknest windblown sand deposit and the Sheepbed mudstone. SAM measures gases that are emitted from samples as they are heated and found evidence for nitrates in abundances of up to 1,100 parts per million. Nitrogen is used by living organisms to build DNA, RNA, and proteins. On Earth, Nitrate (NO3) can be formed from atmospheric nitrogen (N2) by (1) living organisms and (2) high-energy events like lightning strikes. There is no evidence that the nitrate detected by SAM was created by life, and it may have formed by high-energy meteorite impacts into the surface. Its presence in Rocknest suggests nitrates may be distributed in windblown sand and dust and may be widespread across the martian surface. The discovery adds to the evidence that ancient Mars may have been a habitable environment. This image is a selfie taken by MAHLI at the Rocknest deposit, and you can see the scoop marks in the sand.