Hole Drilled to Bottom of Earth's Crust

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Hole Drilled to Bottom of Earth's Crust, Breakthrough to Mantle Looms

 

Thu Apr 7,10:22 AM ET

Robert Roy Britt

LiveScience Senior Writer

LiveScience.com

 

Seeking the elusive 'Moho'

 

http://www.livescience.com/technology/050407_earth_drill.html

 

Scientist said this week they had drilled into the lower section of

Earth's crust for the first time and were poised to break through to

the mantle in coming years.

 

 

The Integrated Ocean Drilling Program (IODP) seeks the

elusive "Moho," a boundary formally known as the Mohorovicic

discontinuity. It marks the division between Earth's brittle outer

crust and the hotter, softer mantle.

 

 

The depth of the Moho varies. This latest effort, which drilled 4,644

feet (1,416 meters) below the ocean seafloor, appears to have been

1,000 feet off to the side of where it needed to be to pierce the

Moho, according to one reading of seismic data used to map the

crust's varying thickness.

 

 

The new hole, which took nearly eight weeks to drill, is the third

deepest ever made. The rock collection brought back to the surface is

providing new information about the planet's composition.

 

 

"It will provide important clues on how ocean crust forms," said

Rodey Batiza, program director for ocean drilling at the National

Science Foundation (NSF).

 

 

Already the types of rocks recovered show that conventional

interpretation of Earth's evolution are "oversimplifying many of the

features of the ocean's crust," said expedition leader Jay Miller of

Texas A&M University. "Each time we drill a hole, we learn that

Earth's structure is more complex. Our understanding of how the Earth

evolved is changing accordingly."

 

 

The latest drilling was done at the Atlantis Massif, located at the

intersection of the Mid-Atlantic Ridge and the Atlantis fracture

zone, two plates of the planet's broken crust. The seafloor is

shallower at the center of this region and therefore easier to reach.

 

 

It's not clear yet whether drilling should continue at the new hole

or if another one should be started in the effort the reach the

mantle. Such work isn't likely to begin again in the next year, said

Barbara John, a University of Wyoming geologist and one of the co-

chief scientists on the expedition.

 

 

"We need to evaluate all the data we have from the cruise and re-

analyze the seismic data, to determine whether it's better to deepen

the current hole or drill elsewhere, or maybe even collect additional

seismic data to better constrain where to drill," John told

LiveScience. "Our major result is that we've recovered the lower

crust for the first time and have confirmed that the Earth's crust at

this locality is more complicated than we thought."

 

 

John said mantle material will be evident when and if it's brought up

because it will have different texture and chemistry and will contain

different proportions of minerals compared with rock in the crust.

 

 

Drillers use the vessel JOIDES Resolution. The 10-year, $1.5 billion

program is funded by the NSF and Japan's Ministry of Education,

Culture, Sports, Science, and Technology.