The combination of low temperature and high pressure found at the bottom of Earth's oceans make methane clathrates very stable. It is thought that as much as 20 times the current known reserves of natural gas may be contained within ocean-floor clathrate deposits, representing a potentially important future source of fossil fuel. Methane clathrates remain stable at temperatures up to 18 °C. The average methane clathrate hydrate composition is 1 mole of methane for every 5.75 moles of water, though this is dependent on how many methane molecules "fit" into the various cage structures of the water lattice. The observed density is around 0.9 g/cm3. One liter of methane clathrate solid would therefore contain, on average, 168 liters of methane gas (at STP).
Sudden release of methane clathrate has been hypothesized as a cause of past climate changes, because methane is a greenhouse gas.
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