Children dream about digging deep holes. Some adults do, too.
Earlier in December I caught up by phone with Henry Dick, a geologist at the Woods Hole Oceanographic Institution. At the time he was two days south of the island of Mauritius, steaming along at 11 knots in high seas aboard the research vessel JOIDES Resolution. His destination, still more than a week off, was a rise in the seafloor below the Indian Ocean, where he intended to begin drilling the first ever hole all the way through the earth's crust and into its mantle.
"We will drill day and night on the hole," Dick says. "We will drill as deep as we can in the time we have allotted. A lot of that depends on weather."
For Dick, it's a return trip of sorts. In 1997 he led an expedition to a spot close to where he'll be drilling now. The ocean floor is favorable there for this kind of work because the crust is as few as 3 miles thick, compared to on land where it is 20 to 30 miles thick, far too deep to drill. Dick's first trip was going well until nature intervened: A huge wave swept by, lifting the ship up and dropping the drilling pipe on a ledge 1,500 feet down the drill hole. It snapped off, and "400,000 pounds of [drilling] pipe went straight down that hole and permanently blocked it," Dick says. "It was a huge disappointment." He adds, "I've been working on this expedition for 31 years."
The impulse to drill all the way through the earth's crust is partly an impulse of pure exploration, like going to the moon.
"This will be first time in human history that we've been able to explore one of the most widespread and fundamental boundaries of earth's layers," says Charles Langmuir, a geochemist at Harvard University.
The trip is also full of scientific consequence. Dick and his team, which includes 30 other scientists from a wide range of fields, will drop a drill through 700 meters of water down to the top of a seafloor mountain, where they'll start boring down into the earth. Every 9.5 meters they'll bring a core sample back to the surface. The first people to examine it will be the biochemists, who will look for signs of bacterial life in the long-anticipated "deep biosphere." Later analysis will look at, among other things, the source of the alternating magnetic stripes fixed into layers of the basalt crust.
"We'll be drilling through an interval of rock that we think represents a reversal of the earth's magnetic field," Dick says. "No one understands how those magnetic stripes are hosted. For the first time we're going to drill through a positively polarized batch of rocks to a negatively polarized batch and back to positive."
The biggest scientific question the crew hopes to answer is the composition of the crust itself. Geologists have never managed to obtain a complete cross-section of the crust, which forces them to make educated guesses about what it is made of. A common approach is to study rocks that begin in the lower crust and rise to the surface in lava flows. These emerged rocks could be a faithful representation of the parts of the crust we can't reach. It's also possible that they change somehow through the process of advancing to the surface, in which case the rocks we receive would be fundamentally misleading about what lies below.
"My work is based on the idea that we can use lavas that come out of the top to infer what the bulk crust is," says Langmuir. "This whole edifice of our understanding of what [lavas] tell us about the earth's deep interior could be built on a house of cards."
Dick's expedition intends to lay that question to rest. Substantial challenges lie ahead, though. Drilling through hard rock half-a-mile below the surface of the ocean is an intrinsically chancy effort. Beyond that, the drill site is adjacent to a hurricane zone and in an area frequented by pirates.
"It's one of the new added joys of going to sea," Dick says. "We have fire hoses to repel boarders."
The team intends to drill for 40 days and hopes to open a hole a little less than 1 mile deep. That by itself won't be enough to traverse the crust, but it would be an important start. If the drilling goes well over the next month, there are plans to come back in two to three years to deepen the hole to 2 miles and then, four to five years later, to bring in a more advanced Japanese drilling ship that would dig down to 4 miles and finish the job. It's a long time to wait for an eager scientific community, but while the crust has many features that make drilling inconvenient, it has one that helps: It's not going anywhere.
Kevin Hartnett is a writer in South Carolina. He can be reached at firstname.lastname@example.org.