Every gallon of gasoline pumped into your car is the prehistoric compressed biomass equivalent of about 40 acres of wheat, by ecologist Jeff Dukes' calculations.

The former University of Utah researcher was driving a university-owned SUV, "and I was thinking of all the gas we were burning and I wondered what that gas was made of originally. How much plant material did it take to make that?"

He researched published geophysical, biological and industrial data to estimate how much carbon from prehistoric plants wound up in fossil fuels, and he calculated it took about 98 tons of grasses, trees and plankton to make the crude refined into one gallon of gasoline.

His calculations were published in the November issue of the journal Climatic Change.

The numbers illustrate how heavily modern life relies on prehistoric life.

"It's a different way of looking at things," Dukes said. "It might help us appreciate how valuable the fossil fuels are. It's amazing to think how much (energy) has been concentrated."

For example, 98 tons of plant matter equals all of the wheat, including stalks, seeds and roots, that grows on 40 acres of land.

"Having to pile 40 acres of wheat plants into your tank just to drive 20 miles, that would be a lot of work," Dukes said. "It's nice that history and geology have done that for us, along with oil companies."