The presence of methane is significant because the gas cannot exist for long. Calculations indicate that sunlight and chemical…

“The presence of methane is significant because the gas cannot exist for long. Calculations indicate that sunlight and chemical reactions in the Martian atmosphere would break up the molecules within a few hundred years, so any methane there now must have been created recently. It could have been created by a geological process known as serpentinization, which requires both heat and liquid water. Or it could be a product of life in the form of microbes known as methanogens, which release methane as a waste product.”

–‘A Great Moment’: Rover Finds Clue That Mars May Harbor Life - NYTimes.com (viaiamdanw)