Mantle Drill

Deep below the our feet, past the thin crust of our planet, lies the mantle. Despite making up the vast majority of the Earth’s mass, we know very little about the composition of this region. What could be there? Mole-men? Crab people? Probably nothing so fanciful, but a team of international researchers are about to find out. At an estimated cost of $1 billion, geologists headed by the Integrated Ocean Drilling Program (IODP) are preparing to start drilling into the mantle for the first time.

The mantle is a 3000 km thick layer of super-heated, mostly solid, rock that fills the space between the human-dominated crust, and the dense iron-rich core. It is believed that knowing more about the makeup of the mantle could have significant impact on our understanding of the origins and nature of Earth. Everything from seismology to climatology and plate tectonics could be affected.

This isn’t going to be an afternoon excursion to the drilling rig, though. It’s going to take a long time to reach the mantle, which is a minimum of 6 km beneath the crust under the best conditions. After considering various methods, researchers have decided to drill through the crust in the Pacific Ccean, which is the only place the 6 km figure holds true. On dry land the crust can be ten times thicker.

To reach the mantle, scientists will be using a custom-built Japanese drilling rig called Chikyu. The Chikyu was first launched in 2002, and is capable of carrying 10 km of drilling pipes. The team is going to need most of that to get down the the seabed and through to the mantle. The Chikyu holds the current deep sea drilling record, having made it 2.2km into the seafloor. This will be a much greater challenge.

EarthThe goal is impressive all on its own, but it isn’t until you look at the logistics of making it all work that you realize what a monumental undertaking this is. The high-tech drill bits being used to bore down into the crust only have an active lifespan of 50-60 hours. After that, the team will have to back out of the hole, change the bit, and plunge back down to the murky depths. To top it off, the borehole is only a 30 cm across… and at the bottom of the sea.

One researcher involved in the project, Damon Teagle, described this procedure as trying to align a steel tube the width of a human hair with a 1/10mm hole when it’s at the bottom of a swimming pool. Certainly accomplishments like the Curiosity/MSL landing are an example of great science, but here we have some amazingly precise science happening right on Earth.

With the technology available today, researchers at the IODP believe that it will take years to reach the mantle. It’s going to be time consuming to change out those drill bits every few days. Teagle suspects that the project could get underway within the next few years. Barring a significant advancement in drilling technology, we should get our first samples from the mantle in the early 2020s.

This project might not have the sexiness of landing a rover on Mars, but it has the potential to vastly increase our knowledge about the evolution and fate of our planet. For the time being it’s the only one we’ve got, so that’s important knowledge to have.