Quest to Drill all the way down to the Earth's Mantle Restarts

In what can only be described as a mammoth undertaking, scientists, led by British co-chiefs, Dr Damon Teagle of the National Oceanography Centre in Southampton, England and Dr Benoit Ildefonse from Montpellier University in France, have announced jointly in an article in Nature that they intend to drill a hole through the Earth’s crust and into the mantle; a feat never before accomplished, much less seriously attempted.


The Earth’s mantle is the part of the planet that lies between the crust and the iron ball at its center, and to reach it, would require drilling down from a position in the ocean, because the crust is much thinner there. Even still, it would mean drilling through five miles of solid rock. And if that doesn’t sound hard enough, temperatures increase the farther down you go, and could reach as high as 1,050 degrees Fahrenheit; high enough to render useless most modern drill bits. Last but not least is the problem of atmospheric pressure, which increases the deeper you go, to somewhere in the neighborhood of 4 million pounds per square foot near the mantle. That last one may not seem like much of a problem, but with exploratory drilling, it becomes a problem rather quickly when you remember that it’s not just a hole they plan to dig, but a hole that can be used to extract samples from very far below.

To retrieve a sample, the drillers would have to rely on drills without a riser (drills that use double pipes for venting gases) which would mean pumping seawater down into the hole through the drill pipe with sufficient pressure to force whatever is being dug back up to the surface so that it can be examined.

 The Deepest Hole in the World

The Kola Superdeep Borehole (1970 - 1994) reached 12,262 metres into the Earth's crust but never reached the mantle. They made it only 0.2% of the way through the Earth [Edit: this is shown as a different percentage in the source documentation referenced later in my answer, due to an apparent error by the author of that publication]. Discoveries included new drilling techniques and sensor instruments, as well as 4 billion year old water manufacturing processes, and 24 species of microbes in unexpected rock formations dating to the dawn of life on Earth.

 

"Over forty years ago, researchers in the Soviet Union began an ambitious drilling project whose goal was to penetrate the Earth’s upper crust and sample the warm, mysterious area where the crust and mantle intermingle— the Mohorovičić discontinuity, or “Moho.” So deep is this area that the Russian scientists had to invent new ways of drilling, and some of their new methods proved quite inventive. " - The Deepest Hole by Alan Bellows

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

 Scientist said this week they had drilled into the lower section of Earth'scrust 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 into the floor of the sea, according to the National Science Foundation (NSF). The rock collection brought back to the surface is providing new information about the planet's composition.

Scientists Are Working to Drill a Mile-and-a-Half Hole Into the Earth

On the seafloor at a location in the Indian Ocean called the Atlantis Bank, about 800 miles southeast of Madagascar, scientists are working to drill 1.6 miles through the Earth's crust to reach the mantle and recover a sample for the first time. Though fragmented pieces of the mantle that were uplifted to the surface by ocean ridges or spewed out by volcanoes have been recovered in the past, the samples have been significantly altered by their journeys to the surface. A pure sample of the mantle—which makes up about 68 percent of Earth's mass and about 85 percent of its volume—could help scientists answer a number of questions about the way material flows between Earth's core and crust. The composition and mineralogy of the mantle will also offer clues about the early formation of the Earth and how it separated into the tiered planet we have today.