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Where Do Potato-Sized Diamonds Come From, 10-Year Project Asks

WASHINGTON, D.C.—“Carbon is arguably the most important substance on the planet,” mineralogist Robert Hazen of George Mason University in Fairfax, Virginia, and the Carnegie Institution for Science told an audience today. “And yet we are profoundly ignorant about deep carbon in the interior of this planet.”

It’s not A Journey to the Center of the Earth, but a project called the Deep Carbon Observatory that will bring together hundreds of scientists to study the movement and fate of carbon thousands of kilometers under ground. They’ll use experiments and observations made here on the surface to explore this “deep carbon cycle.” Hazen’s lecture, here at the annual meeting of the American Association for the Advancement of Science (which publishes ScienceNOW), laid out the questions the effort is beginning to ask. Estimates of total carbon are fairly good for Earth’s atmosphere, seawater, and crust. “What about the mantle? What about the core?” said Hazen. “We don’t know how much is down there. We don’t know how it moves. We don’t know the extent to which there might be organic carbon [deep in the planet]. How much carbon does Earth hold?”

“We don’t know how diamonds grow. There are diamonds the size of potatoes, but where did they come from?” Hazen said. Diamonds shoot up through the crust from a depth of 100 kilometers “without getting degraded into graphite. It must happen in an hour,” mineralogists believe. “How do fluids move that fast?”

Other questions the project is tackling could have profound impacts on Earth’s climate—for example, how the greenhouse gas methane behaves in the depths. “We don’t know how much methane lies on the ocean floor, we don’t know about how it changes,” Hazen said. Still, other questions go literally to the heart of our planet. Earth’s core is made of nickel and iron, but seismologists think it is slightly lighter than they would expect. “Carbon could be a key component,” Hazen said.

The project hopes to explore exotic forms of carbon, including polymers of carbon dioxide found only at superhigh pressure in the mantle. A major tool of the observatory—“We called it that because we are observing carbon with a variety of tools,” said Hazen—is the diamond anvil cell, which recreates the massive pressures and temperatures found within the planet. Using a beam of neutrons, scientists at Oak Ridge National Laboratory in Tennessee will study how fluids move through hot rock samples. Monitoring volcanoes and the areas that flank them will improve scientists’ understanding of what occurs within them. Experiments with microbes persisting under intense pressure and temperature could give clues about life found dozens of kilometers below the surface.

Hazen, who co-leads the effort, says the researchers are modeling the Deep Carbon Observatory on the Census of Marine Life—another 10-year project underwritten by the Alfred P. Sloan Foundation in New York City. Sloan provided about 10% of the $650 million price tag for the census, leveraging the money with other public and private donations to support some 2700 collaborators from 80 nations.

See our complete coverage of the 2011 AAAS annual meeting in Washington, D.C.

This item has been updated to note that Hazen is also at the Carnegie Institution for Science.