The BGB

Post: #1 (ID: 95036)

May 16, 2006
Scientist at Work | Douglas Wilson
With Time Running Out, a Discovery Deep in the Crust of the Earth
By EMILY B. HAGER

It was not exactly a journey to the center of the earth. But if it succeeded, it would take geologists through the earth's crust for the first time ever.

Last November, Douglas Wilson, a geophysicist at the University of California, Santa Barbara, led a team of 120 scientists and crew members aboard the research ship Joides Resolution to a spot 500 miles off Costa Rica. Two miles beneath the surface of the Pacific Ocean, the location had the uninviting name Hole 1256D.

The venture was part of the Integrated Ocean Drilling Program, an international effort that is an outgrowth of Project Mohole, the ultimately fruitless effort in the 1950's and 60's to drill some seven miles through the earth's crust and down into its middle layer, the mantle.

The Wilson team's goal was narrower: using a 10-inch-wide drill, they wanted to reach the bottom of the oceanic crust, a granitelike layer known as gabbro, nearly a mile beneath the seafloor.

If they did, it would be a first. While marine geologists had previously pieced together the crust's architecture from rock samples collected around the world, they had never harvested all its layers together from one spot. So they had never been able to confirm their theories of how oceanic crust is formed.

Dr. Wilson, a wiry, bearded 49-year-old scientist, first zeroed in on the area around Hole 1256D while doing some geological detective work in the 1990's.

According to a hypothesis proposed in 1992 by Dr. G. Michael Purdy of Columbia University's Lamont-Doherty Earth Observatory, the upper layers of the ocean's crust are thinner in places where the new crust forms rapidly.

When new crust forms, it locks in the direction of the earth's magnetic North Pole. Several times every million years, the North Pole and the South Pole flip back and forth. The North Pole becomes the South Pole and vice versa.

Using a device called a magnetometer, Dr. Wilson was essentially able to see stripes of north and south magnetization on the seafloor near Hole 1256D. Because scientists have an established record of when the earth's polarity flipped, they can use these magnetic stripes to help figure out the age of the seafloor and how quickly it formed.

Dr. Wilson calculated that the crust around Hole 1256D was formed some 15 million years ago. Lava erupted from the East Pacific Rise, a long narrow volcanic ridge, and spread out onto the seafloor to harden and form new crust at a rate close to 8.5 inches a year, much faster than at any place on earth today.

On that basis, Dr. Wilson figured that Hole 1256D promised the best chance of reaching gabbro.

"This would basically be the only place on the planet that you could do this," said his longtime colleague Jeff Alt, who is a geochemist at the University of Michigan and was co-chief scientist on the expedition.

Geologists use ultrasound waves to map the earth's crust, bouncing them through layers of rock and reading the patterns that emerge from the boundaries between layers. On the basis of previous measurements, Dr. Wilson estimated that his team would have to drill down 1,397 meters, seven-eighths of a mile below the seafloor, to reach gabbro. That is not terribly deep compared with, say, oil drills, but the team would be cutting through solid rock, not sandy soil.

"The conditions were poor and getting worse," Dr. Wilson said in a telephone interview. On a good day, the drill team hauled up 15-foot-long cores filled with charcoal-black rocks about the size of a man's palm. But through much of November, each time they lowered their drill to bite into the bedrock, the cores came up nearly empty.

Then in early December, 1,372 meters down into the hole, the drill bit broke. As the team spent the next week fishing pieces of it from the hole, anxiety on the ship rose. It had taken more than 10 years to plan the trip, they had missed their Thanksgiving dinners and were about to miss all of December's festivities, and each day on the ship cost about $60,000.

"We knew we had a little more than two weeks of drilling left," Dr. Wilson said, "and we were not at all confident that two weeks was enough to sample gabbro."

On the evening of Dec. 12, with only one week of drilling left, a lab partner of Dr. Wilson turned to him, pointed to a little white stripe in a slate-gray rock, and said, "Hey, this is interesting." Dr. Wilson agreed.

The next morning, another core was swung aboard. It was mostly filled with the usual black rock, but again its bottom was white and this time slightly more granular. That afternoon, Core No. 214 was brought up. At a depth of 1,407 meters below the seafloor, just 10 meters deeper than Dr. Wilson had predicted, the Joides Resolution team reached gabbro. Whoops and yee-haws erupted on deck.

Dr. Wilson's team reported its finding on April 20 in the online version of the journal Science, adding that capturing gabbro as part of a continuous sample of oceanic crust would have two distinct benefits: helping to refine the models of how the crust was formed and calibrating the tools used to see inside the earth.

Preliminary studies of the rocks taken from the drill hole also suggest that the transition between each layer of the earth's crust is controlled not only by changes in rock type and the size of crystals inside the rocks, as previously thought, but also by changes in the rock's porosity. Finally, the researchers confirmed for the first time that gabbroic rock was closer to the ocean floor in places where new crust was formed at a rapid rate.

Dr. Purdy, who is now director of Lamont-Doherty, called Dr. Wilson's achievement "extremely important and fundamental" to understanding the earth's structure. But he said it also demonstrated how little scientists knew about the planet.

"Right now if we're getting excited about knowing only what's 1.4 kilometers beneath the surface, then that's telling you that we don't know much about the deep earth structure," Dr. Purdy said in an interview.

Dr. Wilson is the first to point out that 1256D is just one hole and that there are many more details about ocean crust formation to figure out. He plans to return next year.

Copyright 2006 The New York Times Company

Post: #2 (ID: 112831)

wouldn't all the sea water rush in, and cool the mantle ? Confused

Post: #3 (ID: 112834)

Not nearly enough water, actually.

Post: #4 (ID: 112848)

Well... Ok, then wouldn't we lose the sea?

Post: #5 (ID: 112850)

Nope. Try Wiki-ing the volume of the planet, and then for comparison, the volume of the Earth's oceans.

Post: #6 (ID: 112852)

well you said there wouldn't be enough water... make up your mind!!

Post: #7 (ID: 112873)

That is a question my science students always ask, regarding the Mid-ocean Ridge and the production of new seafloor.
The intense heat and pressure from even a relatively shallow depth would vaporize the sea water almost instantaneously. And then, as soon as the entire drilling apparatus is removed, the pressure will force the shaft to collapse into itself, sealing the hole.

"Well... Ok, then wouldn't we lose the sea? " Where would it go? Rolling Eyes