New York:Hydrogen may not be as rare as once thought as a new study says that rocks beneath the ocean floor by fast-spreading tectonic plates may be a large and previously overlooked source of the gas, which might be the fuel source responsible for triggering life on Earth. And, if it were found in large enough quantities, some experts speculate that it could be used as a clean-burning substitute for today's fossil fuels because it gives off high amounts of energy when burned but emits only water, not carbon. Recent discoveries of free hydrogen gas, which was once thought to be very rare, have been made near slow-spreading tectonic plates deep beneath Earth's continents and under the sea. "Our model, however, predicts that large quantities of H2 may also be forming within faster-spreading tectonic plates -- regions that collectively underlie roughly half of the Mid-Ocean Ridge," said Stacey Worman, who led the study while she was a doctoral student at Duke's Nicholas School of the Environment, Duke University, Durham. Total hydrogen gas production occurring beneath the oceans is at least an order of magnitude larger than production occurring under continents, suggests the new model described online in the journal Geophysical Research Letters. "A major benefit of this work is that it provides a testable, tectonic-based model for not only identifying where free hydrogen gas may be forming beneath the seafloor, but also at what rate, and what the total scale of this formation may be, which on a global basis is massive," study co-author Lincoln Pratson, Professor at Duke. The new model calculates the amount of free hydrogen gas produced and stored beneath the seafloor based on a range of parameters -- including the ratio of a site's tectonic spreading rate to the thickness of serpentinized rocks that might be found there. Serpentinized rocks -- so called because they often have a scaly, greenish-brown-patterned surface that resembles snakeskin -- are rocks that have been chemically altered by water as they are lifted up by the spreading tectonic plates in Earth's crust. Molecules of free hydrogen gas are produced as a by-product of the serpentinization process. "Right now, the only way to get H2?to use in fuel cells, for example?is through secondary processes," Worman, who is currently a postdoctoral fellow at the University of Texas at Austin, explained. "You start with water, add energy to split the oxygen and hydrogen molecules apart, and get H2. You can then burn the H2, but you had to use energy to get energy, so it's not very efficient," Worman noted.