The Germans began their own superdeep borehole project in Credit: Jochem Kueck. However, all of these expeditions ended in a degree of frustration. There were false start and blockages. Then there were the high temperatures their machinery encountered that deep underground, the cost and the politics — all of which put paid to the dreams of the scientists to drill deeper, and break the record for the deepest hole. Two years before Neil Armstrong walked on the moon, US Congress cancelled the funding for Project Mohole when costs began to spiral out of control.
Then it was the turn of the Kola Superdeep Borehole. Drilling was stopped in , when the temperature reached C F. This was twice what was expected at that depth and drilling deeper was no longer possible. Following the collapse of the Soviet Union there was no money to fund such projects — and three years later the whole facility was closed down. Now the desolate site is a destination for adventurous tourists. The German borehole has been spared the fate of the others. The huge drill rig is still there — and a tourist attraction today — but today the crane just lowers instruments for measurement.
The site has become in effect an observatory of the planet — or even an art gallery. Others thought they could hear the planet breathe. Then where we were drilling was just much hotter than where the Russians were.
It was pretty clear that it was going to be much more difficult for us to go any deeper. In his honor, we now call that boundary the Moho [source: Osman ]. Since then, scientists have managed to learn a bit more about the mantle, the layer that lies beneath the Moho, which amounts to 83 percent of the Earth's volume and 67 percent of its mass Encyclopaedia Britannica. The thick outer layer of glazed chocolate and baked dough is solid but elastic. That's the crust.
Underneath that, though, there's a lot of viscous, gooey stuff. Of course, that's a limited analogy, because the Earth isn't cream-filled. Instead, the mantle is made of molten, fluid rock called magma.
Some of that magma is ejected by volcanoes , so we know that in the upper part of the mantle — that is, the top or so miles 1, kilometers — it seems mostly to be composed of oxides of silicon, magnesium and iron, with smaller amounts of aluminum oxide, calcium oxide and alkalies thrown into the mix [source: Encyclopedia Britannica ].
That said, our knowledge of the mantle is fairly limited. Scientists can't go down and look at it, and they've never had a pure sample taken directly from the deep to analyze. That's what the MoHole to the Mantle project hopes to accomplish. It's going to be pretty tough. We know this because scientists actually tried to do it once before. In the early s, they drilled five holes into the ocean bottom near Guadalupe Island in the eastern Pacific Ocean at a depth of 11, feet 3, meters.
The deepest hole only penetrated feet meters into the crust, just past the sediment on the surface into a sub-layer of hard rock. Unfortunately, they didn't get much farther. Some members of U. Congress thought digging to the mantle wasn't worth the cost, and in , they canceled the project [source: National Academies ].
Nearly a half century later, scientists are hopeful that the U. But the physical challenges of drilling to the mantle remain pretty daunting. The first phase of the project at Atlantis Bank is currently wrapping up, and although they didn't reach their target drilling goal of 4, feet, they did retrieve the largest diameter piece of the Earth's crust ever recovered.
The composition of the Earth's crust can vary drastically depending on the location it was recovered from, making the 7-inch diameter, inch long chunk of cooled magma a valuable sample. Multiple broken drill bits mean that the team only reached a depth of 2, feet below the sea floor, but in addition to the large piece of crust recovered, the expedition provided valuable trial-and-error knowledge for a future expedition.
Another trip to the Atlantis Bank to attempt to drill the full 1. Material in the mantle circulates in much the same way that ocean currents do, though at a much much slower pace. Cool material near the border with the crust slowly sinks down toward the core, while hot material near the border with the core rises toward the surface. A full trip from crust to core and back takes an incredibly long time, however, perhaps as long as 2 billion years.
We have some estimates about the density and composition of the mantle from indirect geological methods. The main hole reaches 10, feet. Industry Trends Can the "Jeopardy! Select From Over , Industrial Suppliers. Receive Daily Industry Updates.
0コメント