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That's a lot of plankton. A new study concludes that more than 1000 tons of ancient plant matter go into every tank of gas.

Fill 'Er Up With Plankton

The average automobile gas tank holds more than 1000 tons of ancient plant matter. Jeffrey Dukes, a terrestrial ecologist at the University of Massachusetts, Boston, has figured it out.

"My wife and I were driving through southern Utah in the lab's big Suburban, and I was thinking about how much gas we were burning," he says. So he decided to trace that fuel to its source: dying phytoplankton.

Dukes put together various bits of information that geologists had published. Only about 2% of the plankton make their way to the ocean floor, where they are buried under thousands of meters of rock. Heat from Earth's core pressure-cooks the remains, about half of which becomes oil. A small fraction of this squeezes toward the surface, accumulating in wells where humans can get at about one-quarter of it.

A lot is lost along the way. Multiplying the losses, Dukes calculates that only 0.01% of ancient plant matter that was in the right place at the right time contribute to the oil we can extract. If two-thirds of the oil is gasoline, 90 metric tons of dying phytoplankton went into making each gallon (roughly 4 liters) of gasoline. That's the equivalent of 16 hectares of wheat. And all the green the planet grows in 400 years wouldn't quite produce the fossil fuels we burn in one, Dukes concludes in a study published in the November issue of Climatic Change.

There is a lot of uncertainty in these estimates, notes Leslie Magoon, a petroleum geologist at the U.S. Geological Survey in Menlo Park, California. Even so, Magoon is intrigued. It's a new approach, he says, and "new things come from new ways of thinking."

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