No. 77: Sep-Oct 1991
What looks like a grayish ice cube, fizzes at its edges, and soon wastes away to a puddle of water? If you wish, you can accelerate the substance's demise by touching a match to it; it is packed with potential energy. The substance is methane hydrate, and it is found in prodigious quantities in oceanic sediments. Each cubic centimeter of methane hydrate contains about 160 cubic centimeters of methane at standard conditions; it is a concentrated source of natural gas. In fact, methane hydrate deposits in the world's oceans hold twice as much carbon as all the coal, oil, and gas reserves on land!
But methane hydrate may be much more than a future fuel source; it may have been humanity's savior in eons gone by; it may be our future nemesis. You see, methane hydrate is very unstable; changes of temperature or pressure on a global basis can trigger the release of immense volumes of this greenhouse gas from oceanic deposits.
For example, when the Ice Ages lowered ocean levels by locking up water in the advancing ice caps, pressures on ocean-bottom methane hydrate lessened and, according to some speculators, released enough gas so that the increased greenhouse heating turned back the Ice Ages. (Was Gaia at work here?)
On the other hand, if present human activities are truly stoking the greenhouse effect, ocean temperatures should rise, possibly destabilizing methane hydrate deposits and thereby aggravating the greenhouse effect. Such positive feedback could cook the biosphere. (Anonymous; "Did Methane Curb Ice Ages," New Scientist, p. 24, May 25, 1991. Also: Appenzeller, Tim; "Fire and Ice under the Deep-Sea Floor," Science, 252:1790, 1991.)
Reference. Discussions of the origin of methane hydrate can be found in ESC5 in our catalog: Anomalies in Geology. For ordering information, visit: here.