Can You Dig It? - The Records of How Deep We've Dug Into the Earth
One of the most common misbeliefs among children is the idea that if you keep digging deeper into the ground, eventually you will find yourself on the other side of the Earth. As an adult, though, you realize how impossible this prospect is. Even with diamonds potentially 40km below in the Earth’s upper mantle to serve as motivation, nobody has managed to tunnel through the Earth’s crust. There have been some pretty impressive attempts but the Earth’s upper mantle, which lies right beneath the crust, remains untouched.
The most common examples of drilling into the Earth are when various oil companies, such as British Petroleum (BP) or Exxon Mobile, establish a new oil well. Though oil deposits can be found at various depths below the ground, the drilling of the past century has exhausted most of the oil deposits anywhere above the 6000ft (1.8km) line. This may sound impressive until you realize that the crust has an average depth of 10km under the 3.6km deep ocean, and an average of 40km on land.
The first scientific attempt to dig through the Earth’s crust began in 1958 with Project Mohole, the American attempt to try and extract a sample of the Earth’s upper mantle. With the Space Race having been in full force for a few years, Walter Munk (a member of the National Science Foundation Earth Science Panel) thought it was time that the world stopped looking at the sky and ventured down beneath the Earth’s surface. The aim of Project Mohole was to venture out into the ocean, where the Earth’s crust is the thinnest, and drill through the crust into the Mohorovičić Discontinuity, also known as the Moho, which is the area separating the crust and the upper mantle.
Working with the American Miscellaneous Society (AMSOC), a group of scientists who focused on the more imaginative and ambitious concepts of the scientific world, Munk approached the National Science Foundation (NSF) for funding for the project. Retrieving a sample of the upper mantle would lead to incredible scientific advances and would allow for a greater understanding of the history of the Earth. Unsurprisingly, Munk and AMSOC were granted funding for the project and plans were put in to action.
The first of the three phases of Project Mohole was conducted in 1961. Five different drill sites under 11,700ft, or 3.6km, of water were set in order to extract preliminary samples of the oceanic crust and to test the effectiveness of the equipment. The deepest drill site only reached a depth of 601ft, less than 1/5 of a kilometer, but provided sediment samples dating as far back as 23 million years ago in the Miocene era. Following this success though, the NSF took control over the project from AMSOC. NSF failed to properly manage Project Mohole and eventually lost government funding, leading to the dissolution of the project entirely.
The second attempt, made on the other side of the world in Soviet Russia, was the Kola Superdeep Borehole Project. Rather than attempting to conduct tests with the restriction of being on a boat, the Soviet scientists decided to begin drilling in the wide open Pechengsky District of Murmansk Oblast, Russia. While it was easier to set up and maintain the drill site, the scientists had to drill through four times as much of the Earth’s crust to get to the same destination Mohole had.
The Kola Project began in May of 1970 and continued on and off, restricted only by mechanical issues, until 1994 when higher than expected temperatures (and the dissolution of the Soviet government) brought the project to an end. At this point the borehole had reached a depth of 40,230ft (12.2km), or 1/3 of the way through the Baltic Shield region of the Earth’s crust, just short of its short-term goal of 49,000ft (15km). Researchers predicted the temperature at this depth to be around 100*C. As they approached this final mark, temperatures reached as high as 356*C, which drastically decreased the effectiveness of the drilling equipment. Researchers operating the drill reported that the rocks at this depth acted more like plastic than normal rock, due to the average temperature and pressure that previously affected them.
While the goal was never reached, the Project was not a failure. In addition to the engineering feat the Kola Superdeep Borehole is, researchers had quite a few impressive discoveries on the way down. First of all, large amounts of hydrogen gas were found at the bottom of the borehole. The concentration was so high that the researchers noted that the mud near the bottom of the hole seemed to be boiling due to how much hydrogen was escaping. Secondly, despite the temperature and pressure, water was present at these depths. It is theorized that the water was created from hydrogen and oxygen being squeezed out of the surrounding rocks due to the incredible pressure placed on them (approx. 28,826psi compared to the 15,000psi at the bottom of the Challenger Deep). The reason the water was still in liquid form is because of this pressure, which drastically increased the boiling point.
In addition to water, researchers found the fossils of 24 different species of single celled organisms while on their way down. At the lowest point, the samples were found to be 2.7 billion years old, meaning that some of these organisms could have been alive when the Earth was a little less than half as old as it is today. While not the earliest known living organisms, the abundance of species at these depths offered a greater insight into some of the earliest stages of the Earth’s life.
Humanity did not give up on trying to reach the upper mantle after the Kola Superdeep Borehole, though. While still over ten years away, a group of international scientists plan to drill through the ocean floor and take the first ever sediment samples from the upper mantle. The research vessel to be used, named Chikyu, has been aiding scientists in waterborne research ever since it was launched in 2005, breaking multiple records in the field of sediment recovery. There are multiple labs aboard that cover a wide variety of scientific disciplines, allowing researchers to study recovered samples before the change in environment can affect them.
According to Natsue Abe, a Japanese researcher aboard Chikyu, this potential project has four main objectives, the first of which being to completely penetrate the Earth’s crust for the first time. The second goal is to study the Moho, or the boundary between the crust and the upper mantle. The third is to gain insight as to how the Earth’s crust was formed billions of years ago. The final goal is to investigate how deep within the Earth microbial life can, or has been able to, exist. The fossils that were found during Project Kola give promise for finding more single celled organisms that have lived, or are currently living, under extreme conditions.
At this point in time, there are three drilling sites being considered for the project; near Hawaii, off the coast of Costa Rica, and somewhere around Mexico’s pacific coast. Similar to Project Mohole, the team aboard Chikyu will have substantially less of the Earth’s crust to drill through to reach the upper mantle. The various drilling sites each consist of a 4km drop through the ocean, followed by 6km of the Earth’s crust, and then 1km of drilling into the upper mantle in order to ensure a pure mantle-filled sample. Seeing as Project Mohole was only limited by the high costs and lack of funding, compared to the depth and temperature that held back Project Kola, this project planned for Chikyu seems very promising. The only limitation is the wait to make sure that the technology used to drill the hole can effectively and economically do the job.
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