Past life on Mars? Here's what new NASA evidence points to.

Cold, dry, and barren: Mars doesn't look like it could be a haven for life — at least not the kind humans are familiar with. 

Despite the Red Planet's appearance, scientists have wondered for decades about the possibility of microbial life inhabiting Mars in the distant past. Now a new study, based on data collected by NASA's Curiosity rover, is peeling back another layer of the mystery. For the first time, researchers measured the isotopic composition of carbon-rich minerals found in Gale Crater...