Slashdot has a story about a possible non-organic source for the methane they’ve detected. According to an article in Nature, Chris Oze, a geologist from Dartmouth College, Hanover, New Hampshire, “and his Dartmouth colleague Mukul Sharma calculated that [serpentinization] would consume about 80,000 tonnes of olivine each year. To spit out methane at the same rate over the planet’s 4.5-billion-year lifetime would require a global, 50-centimetre-thick layer of the mineral, spread a few kilometres below the planet’s crust. That would be just one millionth of the mass of the planet. ‘It really doesn’t take much olivine at all,’ says Oze.”