Renegade Drillers Aim for the Earth's Mantle
October 3, 2012 3:32 PM
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Project will try to drill down 6 km at the crust's thinnest location in the Pacific Ocean
It sounds like a plot of a science fiction movie. But to
, a geochemistry professor at the UK's
University of Southampton
The Integrated Ocean Drilling Program
" (IODP) co-leader, the ambitious effort to be the first humans to drill to the Earth's mantle is dead serious.
I. The Race to the Mantle
While many have long held that such an effort is infeasible given current technology and the expense involved, Professor Teagle and company hatched a bold scheme to venture out in one of three locations in the Pacific Ocean and use deep-sea drilling equipment to tunnel 6 km (3.7 miles) down, eventually hitting the mantle.
On land the Earth's crust is up to 60 km thick, making drilling to the mantle unlikely to succeed with today's technology. But Professor Teagle is convinced that by using deep sea drilling at one of these locations (ocean ridges) where the crust is the thinnest, the mantle can be reached and sampled for "only" about $1B USD.
The effort will require 10 km-long (6.2 miles) drill pipes to drill through the ultra-hard rocks that are though to surround the mantle.
Croatian meteorologist Andrija Mohorovicic first discovered the Earth’s mantle-crust boundary. The mantle is a 2,900 km layer of the Earth's onion-like composition. Composed mostly of silicon dioxide (the same material that sand or semiconductors are made of), temperatures at the crust border range from 500 to 900 °C (932 to 1,652 °F). The mantle, at its molten inner surface touches the
Earth's molten nickel-iron core
, where temperatures reach 4,000 °C (7,230 °F).
Professor Teagle calls the project "the most challenging endeavor in the history of Earth science", comparing it to
the Apollo Program
. He says the project will serve to "inspire" future generations of scientists and will leave a "legacy of fundamental scientific knowledge" -- namely, giving a never-before-glimpsed look at representative mantle chemistry, temperatures, and pressure. According to Professor Teagle, this would be a big step forward as we currently only have a "reasonable" of the Mantle's composition and behavior.
The hardest challenge will be digging through the hard rocks closest to the mantle.
[Image Source: CNN]
He comments in a
, "[The mantle] is the engine that drives how our planet works and why we have earthquakes and volcanoes and continents. We have the textbook cartoons but detailed knowledge is lacking."
II. No Guarantees
The project will make use of a pre-existing Japanese deep-sea drilling vessel named Chikyu. A hulking, lumbering ship Chikyu can carry up to 10 km of drilling pipes and set a scientific deep sea drilling world-record of 2.2 km in early testing. The hole drilled by the IODP drills will be a mere 30 cm in diameter -- or roughly one foot wide.
The Chikyu, at sea [Image Source: CNN]
Professor Teagle gives some perspective on how much a feat this is, commenting, "It will be the equivalent of dangling a steel string the width of a human hair in the deep end of a swimming pool and inserting it into a thimble 1/10 mm wide on the bottom, and then drilling a few meters into the foundations."
The drill bits will need to be replaced every 50 to 60 hours, and additionally special bits may need to be swapped to drill through ultra-hard near-mantle crust layer. That means the project could take more than a year to complete, unless better drill bits can be produced.
The Chikyu can carry up to 10 km worth of pipes. [Image Source: CNN]
The IODP is not the first effort to drill down to the mantle. The first major attempt dates back to 1966 when a team of U.S. researchers drilled off the coast of the eastern Pacific's Guadalupe Island. The project, dubbed "Project Mohole" in honor or Professor "Mo" Mohorovicic, reached only a few meters before it was abandoned.
A land-based project by the Russians in the 1980s in the Kola Peninsula drilled down 12 km into the Earth's crust, earning a record for deepest borehole that still stands. Exxon Mobil Corp. (
) in 2011 drilled a longer borehole (12+ km) in Easter Russia, however the hole was drilled on an angle.
Thus to summarize how close man has came to drilling to the mantle yet, the best answer is "not very close".
The ocean-based effort clearly provides an easier route that is within historic borehole depths (12 km). However, the difficulties of drilling at sea and of penetrating the hard inner crust make success uncertain, even as Professor Teagle's team forges ahead.
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Mantle is not molten
10/3/2012 4:22:30 PM
To correct something from the article and that people are worrying about, the mantle is not molten. The upper portion of the mantle is still part of the lithosphere and is solid and brittle. Below the lithosphere (typically at a depth of about 150 km) you run into the asthenosphere (also part of the mantle) which isn't molten either, but is a soft solid kind of like room temperature butter. At mid-ocean ridges, the asthenosphere is closer to the surface and, due to the decreased pressure, it is able to partially melt. That results in some volcanism at the mid-ocean ridge.
The researchers are not going to poke a hole and get a massive volcano out of some massive underground cavern of molten rock. That's just not the way it is.
RE: Mantle is not molten
10/3/2012 4:27:44 PM
From what I gather, the researchers are trying to drill to the moho boundary where the composition changes from basalt to peridotite. They will still be drilling in a solid when they hit the peridotite.
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