A s the drill bit slowly advances, cutting through 6,000 meters of solid granite, an anxious drill team waits above, in a verdant Swedish forest thick with pine. They come to this geologically unpromising location in search of natural gas. If they find commercial quantities, geologists will have to revise their explanation for the origin of oil and gas -a revision that could mean the earth holds untold reserves of these precious fuels. Most geologists believe that natural gas and oil originate from the decay of buried organic material, hence the name fossil fuels. Dead ocean organisms such as plankton and kelp sink to the ocean floor and are covered by layers of sedimented rock particles. Then, as sediments accumulate over organic layers, pressure, temperature and time break these organic molecules into the heavy hydrocarbons of oil and then into the lighter hydrocarbons of natural gas. Since 1979, astronomer Thomas Gold has attacked this conventional theory by reviving a century-old idea that the principal source of oil and gas is not organic material but the interior of the earth. The modern version of this alternate theory, called the deep-earth-gas hypothesis, begins with the earth's origin. Gold, formerly with Cornell University in Ithaca, NY, claims that the primordial earth received most of its carbon in the form of complex hydrocarbons, which can still be found in many of the meteorites that bombard the earth today As the earth developed and warmed, the hydrocarbons buried within the mantle began to liberate methane, the lightest of the hydrocarbons and the principal component of natural gas. Gold contends that since this early warming, methane and heavier hydrocarbons have been rising to the surface of the earth through open areas of the crust such as volcanoes and fault lines. Lack of evidence has kept most geologists from seriously considering this highly speculative theory At the same time it has been difficult to disprove the deep-earth-gas hypothesis. Right now, however, many eyes are focused on a 44-kilometer-wide Swedish meteor crater named the Siljan Ring, where an ongoing drilling project might provide Gold with much of the evidence he needs. While the drilling project, which includes scientists from the United States, Sweden, Germany, Denmark and Norway, has yet to strike a large methane reservoir, the scientists have already found small amounts of methane and other evidence that might vindicate the deepearth-gas hypothesis. Even the interpretations of these preliminary findings, however, have run into opposition in the scientific community