Re: Hmmmm
There was a strong 'biogenic hydrocarbons' movement in the Soviet Union which hypothesised that olivine in the Mantle, combining with water under high pressures and temperatures was the original source of all hydrocarbon deposits.
According to this hypothesis, the methane would migrate up through fractures in the Mantle and Crust and become trapped in sedimentary structures. The actual evidence for this was always rather lacking and the few case studies of hydrocarbons being found in granitic and metamorphic rocks are rather better explained by migration from sediments through faults; or - much to the embarrassment of the Swedes who sunk an expensive borehole in the Siljan Ring - came from the diesel used to lubricate the bit.
The theory never got much traction in the West where there was abundant research into trace chemicals formed by the decomposition products of porphyrins and the like which are found in oil, and which demonstrated that petroleum is, as always suspected, a fossil fuel.
The only prominent advocate in the West was Thomas Gold, previously famous for the 'Steady State Model' of the Universe which rather overshadowed his contributions to the understanding the interaction of the Sun and the Earth.
The Martian methane is probably coming from the serpentinisation process which involves the hydrolysis of ferromagnesian minerals by high temperature water to produce serpentine group minerals - including serpentinite and talc as well as methane. A side reaction involving iron(II) in olivine produces hydrogen.
A definitive answer should come from isotope abundances in the methane. Life, as we know it, preferentially selects for light carbon isotopes so biogenic methane should show a positive C12/C13 ratio compared to methane released by serpentinisation.