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Today – December 16, 2015 – a drilling rig on a ship has parked above a spot in the Indian Ocean. Here they will begin drilling toward the mantle. The scientists work for the International Ocean Discovery Program. They plan to bore through six kilometres of tough oceanic basalt – the Earth’s crust – and then pierce the mantle. No one has ever drilled into the mantle before, but there have been a half dozen serious attempts.

Decades ago, the Russians drilled deeper than anyone has ever gone. Their Kola Superdeep Borehole was started in 1970 and still holds the world record for the deepest hole in the ground. But they didn’t reach the mantle. As the latest mantle drilling project begins today off the coast of Africa, people are wondering if a billion dollars for the newest hole in the ground is worth the money. We can’t say. We don’t know what the team in the Indian Ocean might learn. But back in the ’70s and ’80s, no one expected the results the Soviets got from their 12,262-metre-deep borehole.

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Here are 6 unexpected discoveries from the world’s deepest well:

There’s a lot of water down there. Hot mineralized water was found almost everywhere along the drill path. Everyone figured that the granite would be as dry as a stone. Who says you can’t get water from a rock? To cut miles into the ground, the engineers had to invent a whole new drill. In the past, drillers quickly spun the entire drillstem so the bit at the bottom could chew the bedrock. Before starting, the Soviets calculated that the tubing would weigh over a million pounds. They could never generate enough torque to rotate that much pipe fast enough to drill through kilometres of granite. So, in 1969, the Soviets invented a rotary bit. It spun by sending pressurized mud down the pipe where it blew through a turbine at the drill head, spinning it 80 revolutions per minute. It worked and the system is now used on oil wells. The Earth has gas. Unexpectedly, helium, hydrogen, nitrogen, and even carbon dioxide (from microbes) were found all along the borehole. There is no basalt under the continent’s granite. This was a huge surprise. Seismic suggested that at 9,000 metres the granite would give way to basalt. It doesn’t. The seismic anomaly that suggested basalt was caused by metamorphosed granite instead. This gave support for plate tectonics, which was a new theory when the Kola Superdeep Borehole was being drilled. There are fossils in granite 6,700 metres below the surface. How’d that happen? Hell is deeper than 12,262 metres. There’s a persistent rumour that the drilling ended in 1992 because scientists pierced a super-hot cavity and heard the screams of damned souls. Not likely. For that, they probably needed to actually reach the mantle.

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