Wednesday, December 2, 2015

Project 'Mohole' Resurrected

Even when I was a young child, first interested in oceanography, scientists were talking about doing this: Quest to drill into Earth’s mantle restarts
In early December, the drill ship JOIDES Resolution will depart Colombo, Sri Lanka, and head for a spot in the southwestern Indian Ocean known as Atlantis Bank. There, it will lower a drill bit and try to screw it through 1.5 kilometres of rock, collecting a core sample as it goes. If all goes well, future expeditions — not yet scheduled or funded — will return and finalize the push into the mantle (see ‘Deep understanding’).

Normally, the crust–mantle boundary is thought to be marked by a feature known as the Mohorovičić discontinuity, or ‘Moho’, at which seismic waves change velocity. But at Atlantis Bank, the mantle is thought to bubble up as far as 2.5 kilometres above the Moho, making it easier to reach.

Reaching these deep-Earth frontiers “is one of the great scientific endeavours of the century”, says Henry Dick, a geophysicist at the Woods Hole Oceanographic Institution in Massachusetts and co-leader of the expedition.
The original attempt was a classic SNAFU:
Scientists first tried to reach the Moho in the middle of the twentieth century. In the 1960s, US scientists led ‘Project Mohole’, which drilled into the sea floor off Guadalupe Island, Mexico. The project reached a depth of just 183 metres before costs ballooned and Congress killed it.
Modern oil drilling goes far deeper than that. The technology has increased dramatically since the 60s.

Scientists already know what they expect to find there:
Ancient Moho zones are exposed above-ground in numerous ophiolites around the world.
But back to the article:
Dick knows that it is possible to reach his preliminary goal of 1.5 kilometres, because he has done it before. In 1997, he led an expedition to Atlantis Bank that got that deep before disaster struck: the pipe snapped off in high winds, corkscrewed down inside the hole and plugged it up. “We’re going to make sure that doesn’t happen this time,” he says.

Along the way, researchers hope to explore not just geology, but biology, too. Geological mapping suggests that seawater may have percolated several kilometres deep at Atlantis Bank, triggering chemical reactions that turn the rock into a type known as serpentinite. These reactions generate methane, a gas that sub-sea-floor microbes often munch for energy. JOIDES Resolution scientists will be checking the rock cores for microorganisms, says Virginia Edgcomb, a microbiologist at Woods Hole who will be on the cruise.
OK, I didn't know that; chemical reactions producing methane? Does that imply an abiological source for some, or much of the natural gas on earth?

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