Diamonds reveal secrets deep down below Earth surface

Scientists believe diamonds can bring information about deep part of the Earth that humans can't get access and don't know much about.

Evan Smith, a diamond geologist at the Gemological Institute of America, said the most valuable of all gemstones are coincidentally some of the most scientifically valuable pieces of the Earth.

Smith first ground some diamonds down and cutting others open, and then used big microscopes, lasers and electron beams to figure what was inside. He also used a magnet attached to a string to figure out if they contain iron.

Eventually, he found that many of the stones contained bits of garnet with a silicon content, which means that very high pressure were involved in their formation.

He also found iron and nickel, shrouded in invisible envelopes of fluid methane.

In his conclusion, Smith said these big diamonds originate from extreme depths in the Earth, from about 322 km to 805 km below the surface.

"That's about as far under our feet as the International Space Station is above our heads. And it's about twice as deep as where most diamonds are born," he said.

The other thing he learned is that the diamonds had formed inside oxygen-deprived patches of liquid metal.

That's the first hard evidence that the Earth's mantle is not an entire stew of oxygen-rich rocks.

Scientists believe that the mantle, the part of the planet between the continental plates and its core, would be pretty thoroughly mixed, with oxygen distributed throughout. But these diamonds show that there were pockets that somehow managed to resist that mixing.

"It tells you that we have to refine our thinking about how the planet evolves with time. And that our simple pictures may not be good enough anymore if we can't explain these features," says Kanani Lee, a mineral physicist at Yale University.

source: Xinhua