Phase diagram showing the water depths (and pressures) and temperatures for gas hydrate (purple area) stability. Windows to the Deep will explore areas of the Blake Ridge and Carolina Rise in which the uppermost sediments lie within the range denoted by the green box. The red line shows a geotherm or temperature in the Earth as a function of depth. Note that, at greater depths in the sediments, the geotherm crosses from the hydrate zone (purple region) to the gas zone. This means that gas hydrate in sediments usually overlies free gas.