Is it possible to dig all the way down to the Earth's mantle?

Main Points

Remember the excitement of digging in the sand at the beach as a child? With a plastic shovel, you dug deeper and deeper, wondering how far you could go. Would you really end up in China, as your sibling joked? Of course, you never got to finish your digging adventure, as it was time to pack up and get an ice cream. Yet, in the back of your mind, the question remains: what would happen if someone dug a truly, truly deep hole?

You might not have to wonder anymore, as an international team of scientists known as the 2012 MoHole To the Mantle project aims to make it a reality. Their $1 billion mission, backed by global support, involves a Japanese deep-sea drilling vessel, the Chikyu, which will drill through the Pacific Ocean floor, going deeper than ever before. Their goal is to break through the Earth's crust, the rocky outer layer, which ranges from 18 to 37 miles (30 to 60 kilometers) thick on land, but can be as thin as 3 miles (5 kilometers) under the ocean floor [source: Osman]. If the Chikyu's drill reaches the Moho, a boundary layer, it will tap into the Earth's mantle, a mysterious 1,740-mile (2,900-kilometer) thick layer sitting between the crust and the molten core [sources: USGS, ScienceDaily].

Unlike the childhood fantasy of digging straight through the planet, scientists have no intention of boring a tunnel from one side to the other. Such a feat is likely impossible due to the immense heat and pressure deep inside the Earth, which would make traversing such a tunnel unfeasible, even if it didn't collapse. However, reaching the mantle, a layer that is still poorly understood, and retrieving a sample would be an extraordinary scientific achievement—one that some have likened to geology's version of the moon landing. In this article, we'll explore the immense difficulty of drilling so deep and the potential insights we could gain from it.

What Lies Beneath: The Earth's Mantle

It's remarkable to think that we're spending $1 billion to drill through the Moho, especially considering that just over a century ago, scientists didn't even know it existed. In 1909, Croatian researcher Andrija Mohorovičić discovered that seismic waves from earthquakes traveled faster about 20 miles (50 kilometers) beneath the Earth's surface, suggesting a distinct boundary between the crust and a different layer below. This discovery helped establish the existence of the Moho, a boundary now named in his honor [source: Osman].

Since then, scientists have gathered more insights into the mantle, the layer beneath the Moho, which makes up 83 percent of the Earth's volume and 67 percent of its mass Encyclopaedia Britannica. To grasp this, imagine the Earth as a chocolate éclair. The thick outer layer, resembling glazed chocolate and baked dough, is solid but flexible. This is the crust. Beneath it, however, lies a viscous, molten substance. While the analogy is limited—since the Earth isn't filled with cream—the mantle consists of molten rock known as magma. Some of this magma is released through volcanoes, so we know that the upper part of the mantle, roughly the top 620 miles (1,000 kilometers), consists mainly of oxides of silicon, magnesium, and iron, with smaller amounts of aluminum oxide, calcium oxide, and alkalis [source: Encyclopedia Britannica].

That said, our understanding of the mantle remains relatively shallow. Scientists can't directly observe it, and no pure sample has ever been taken from such depths for analysis. This is precisely what the 2012 MoHole to the Mantle project hopes to achieve.

What Does It Take to Dig That Deep?

It's going to be extremely challenging. We know this because scientists attempted a similar feat in the 1960s. They drilled five holes into the ocean floor near Guadalupe Island in the eastern Pacific Ocean, at a depth of 11,700 feet (3,566 meters). The deepest hole reached just 600 feet (183 meters) into the crust, barely penetrating the sediment layer to touch the harder rock beneath. Unfortunately, progress halted there. Members of the U.S. Congress deemed the endeavor too costly, and the project was canceled in 1966 [source: National Academies].

Nearly 50 years later, scientists remain hopeful that countries like the U.S., Japan, and others will pool resources to fund the mission. However, the physical obstacles involved in drilling to the mantle are still daunting. Even with the thinnest section of the crust on the ocean floor, they would need to drill through several miles of solid rock. To make matters worse, as they go deeper, they will face extreme heat—possibly surpassing 1,000 degrees Fahrenheit (538 degrees Celsius)—and immense pressure, potentially reaching 4 million pounds per square foot near the mantle. This tremendous force will make it a challenge to keep the equipment functioning and to bring the excavated material back to the surface for analysis [source: Yirka].

On the bright side, in the last 50 years, thanks to deep-water drilling by the oil industry, drilling technology has made huge strides. We now have stronger drill bits, tools, and instruments that can endure extreme heat and pressure. With advancements in GPS and other technologies, keeping a drilling ship precisely in place in the deep ocean has become much easier. Additionally, researchers have gained a better understanding of the oceanic crust, its formation, and the differences between the crust and mantle, according to Damon Teagle from the National Oceanography Center in Southampton, England, one of the project's leaders. "We have a much better understanding of what we are trying to do," he explained in a 2011 interview [source: Cooper].

If there are no unexpected setbacks — a big if, of course — the scientists expect it to take about 18 months to two years to reach the mantle. They plan to begin in 2013 or the following year and hope to finish the project by the end of the decade [source: Cooper].

What Can We Learn From Digging to the Mantle?

Hopefully, a lot. As mentioned before, our knowledge of the Earth's mantle is limited because we can't physically explore it, and no pure sample has ever been obtained. Instead, scientists have tried to learn about it by studying seismic waves and the molten rock expelled by volcanoes. They've also examined meteorites, which are made of the same cosmic material as the Earth, for clues about the mantle's composition [source: Osman].

However, these methods leave many questions unanswered. If scientists are able to retrieve and study the mantle directly, they could unlock new insights into how the Earth formed billions of years ago, how it evolved into its core, mantle, and crust, and how plate tectonics originated. By analyzing the exact mixture of chemicals and isotopes in the mantle, they could better understand how the mantle transfers materials to the Earth's surface [source: Osman].

More crucially, they may uncover how the movement of the mantle's molten rock influences the Earth's crust, particularly how the tectonic plates interact by pushing and pulling against each other [source: Cooper]. Gaining a deeper understanding of the mantle and its relationship with the crust could eventually help us predict natural events like earthquakes and volcanic eruptions [source: Matsu'ura].

One of the most exciting possibilities is that scientists might discover life deep beneath the Earth's surface. We're not referring to the fantastical creatures from Jules Verne's "Journey to the Center of the Earth," but rather tiny, resilient organisms known as extremophiles, which have adapted to survive extreme pressures and temperatures (like the microscopic "worms from hell" found in a South African gold mine). Such organisms have already been discovered on the deepest ocean floor. If they can survive even deeper within the Earth, scientists believe these organisms could contain unique enzymes or other properties that may be applied in biotechnology development. More importantly, they could offer insights into the physiological limits of life itself [source: Osman].