How Hard Is It to Dig That Deep?
It's going to be pretty tough. We know this because scientists actually tried to do it once before. In the early 1960s, they drilled five holes into the ocean bottom near Guadalupe Island in the eastern Pacific Ocean at a depth of 11,700 feet (3,566 meters). The deepest hole only penetrated 600 feet (183 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.S. Congress thought digging to the mantle wasn't worth the cost, and in 1966, they canceled the project [source: National Academies].
Nearly a half century later, scientists are hopeful that the U.S., Japan and other countries will pool their resources to cover the cost. But the physical challenges of drilling to the mantle remain pretty daunting. Even if scientists find the thinnest possible section of the crust on the ocean bottom, that still means drilling through at least several miles of solid rock. To make things more difficult, as they drill deeper into the Earth, they'll encounter extreme temperatures, possibly in excess of 1,000 degrees Fahrenheit (538 degrees Celsius), and fantastic amounts of pressure — as much as 4 million pounds per square foot in the vicinity of the mantle. With that crushing force squeezing the equipment, it's going to be a challenge to keep it running, let alone to push material that's being excavated back up to the surface, so that scientists can get the samples they want [source: Yirka].
On the plus side, though, in the past 50 years, thanks to deep-water drilling by the oil industry, drilling technology has advanced significantly. We've got improved drill bits, tools and instruments that are much more able to withstand heat and pressure. And thanks to GPS and other advances, it's much easier to keep a drilling ship in exactly the same spot in deep water. Researchers also now know more about the ocean crust and how it is formed, and about the differences between the crust and mantle, according to Damon Teagle of the National Oceanography Center in Southampton, England, one of the leaders in the project. "We have a much better understanding of what we are trying to do," he explained in a 2011 interview [source: Cooper].
If the scientists don't encounter unforeseen snafus -- which is a big if, of course -- it could take them between 18 months and two years to drill down to the mantle. They hope to start in 2013 or the following year and complete the project before the end of the decade [source: Cooper].