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Drilled Core Exposes Hitherto Unseen Layer of Earth's Crust

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Nikkohl Gallant
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« on: May 21, 2008, 11:37:17 pm »

April 21, 2006 


Drilled Core Exposes Hitherto Unseen Layer of Earth's Crust
TEXT SIZE:   By David Biello


 

IODP/TAMU
Since the 1950s, scientists have been trying to drill through the oceanic crust to expose the mantle below. Although that goal remains out of reach--the crust is more than four miles thick--a new drilling project at the bottom of the Pacific Ocean has reached almost a mile below the sea-floor and exposed what lies beneath the uppermost layer of crust for the first time.


A team of American and Japanese scientists began drilling at the site--500 miles west of Costa Rica--in 2002, lured by theoretical predictions of thin crust in areas where the sea-floor spread most rapidly. More than 12 million years ago, this region of the Pacific formed new crust at nearly nine inches per year--faster than any spreading occurring today. Because of that quick spreading, the underlying layer of gabbro--coarse-grained, black volcanic rock--should be nearer to the surface, explains team member Doug Wilson, a geophysicist at the University of California, Santa Barbara. "If that theory were to be correct then we should only need to drill a relatively shallow hole compared to anywhere else," he says.


Ultimately, after five months at sea drilling, that relatively shallow hole reached nearly a mile deep. But at roughly 3,900 feet below the ocean floor the drill bit penetrated the overlying crust rock--baked to extreme hardness by the magma beneath it, like tempered steel--and reached gabbros. This marked the first time gabbros have been recovered intact from the depths of the ocean's basement.


Because such formerly oceanic floor currently covers 60 percent of the earth's surface, the core should elucidate how our planet's crust forms. "Having this sample from the deep fossil magma allows us to compare its composition to the overlying lavas," says team member Jeffrey Alt of the University of Michigan. "It will help explain whether ocean crust, which is about six to seven kilometers thick, is formed from one high-level magma chamber or from a series of stacked magma lenses."


The scientists hope to drill deeper yet at the site, uncovering more information about crust formation, but for now the penetration of this rock boundary represents a major milestone. The researchers report their preliminary findings in a paper published online today by Science.

http://www.sciam.com/article.cfm?id=drilled-core-exposes-hith
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Nikkohl Gallant
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« Reply #1 on: May 21, 2008, 11:46:08 pm »

May 14, 2001 


Tectonic Plates Moved Earlier Than Previously Thought
By Harald Franzen

 
A new study published in this week's issue of Science concludes that tectonic movement on earth may have started 500 million years earlier than 1.9 billion years ago, a date suggested by current theory. Timothy Kusky and colleagues at St. Louis University, along with researchers from Washington University in St. Louis, found the oldest complete section of oceanic sea floor on the planet last summer. Oceanic earth crust is usually "recycled" back into the mantle through subduction, but a few fragments survive in mountain belts that form during the collision of two tectonic plates. That is exactly what happened with Kusky's sample, found in a mountain belt in the Eastern Hebei Province in China. The sample turned out to be about 2.5 billion years old, dating back to the Archean?earth's earliest geologic time period.

"This discovery shows that the plate tectonic forces that create oceanic crust on the earth today were in operation more than 2.5 billion years ago," Kusky says. He thinks that these findings could help shed a light on when the first complex organisms evolved on earth: "Because hot volcanic vents on the sea floor have provided the nutrients and temperatures needed for life to flourish and develop, it's possible that life developed and diversified around these vents as plate tectonics began."

http://www.sciam.com/article.cfm?id=tectonic-plates-moved-ear&sc=I100322
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