Not since the drilling of the Russia’s Kola Borehole have scientists ventured this deep.
Japanese scientists have announced a plan to drill through the Earth’s crust and reach the mantle. The major initiative would be a first for humankind. Despite multiple previous attempts and multiple boreholes of significant depth, we’ve never managed to drill far enough to see what lies beneath the Earth’s rocky crust. Instead, our knowledge of the mantle is mostly based on indirect observations, like the speed at which seismic waves propagate through the planet’s internal geometry.
A 2007 investigation into a unique area between Cape Verde and the Caribbean Sea, where the crust of the Earth is missing and the mantle is directly exposed, yielded some fascinating rock samples and scientific data, but not the same information that scientists hope to gather by drilling into the molten layer directly.
The new project, led by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC), will begin by conducting a two-week study off the coast of Hawaii. If this location isn’t suitable, the research team plans to investigate areas offshore from Costa Rica and Mexico. All of the drilling sites are in the ocean because the Earth’s crust is roughly twice as thick on land as it is over water. Even so, this is no small task. Chikyu’s drill will have to pass through 2.5 miles of water and 3.7 miles of crust to reach the mantle, which accounts for ~85% of the Earth’s volume.
We already know that the mantle is comprised of different material than the Earth’s crust. Mantle material has a higher ratio of magnesium to iron than Earth’s crust, but contains less silicon and aluminum than our planet’s surface does. We also know that the mantle slowly circulates thanks to convection currents. As the graph below shows, hot spots deep in the region where the mantle meets the Earth’s core lead to an upwelling of heat several thousand kilometers away.
But beyond these facts, there’s a great deal we don’t know. There are questions regarding how hot spot formation relates to earthquakes and volcanic eruptions on the Earth’s surface, how convection currents interact with tectonic plates, and how the mantle can apparently suffer its own earthquakes at depths of 250 to 420 miles. The Japanese government is helping to fund the Chikyu expedition because it’s hoping the information we gain can be used for earthquake prediction. The research team is hoping to investigate interactions between the crust and mantle to understand how the planet’s crust formed in the first place, and to determine exactly how deep within the earth microbial life can exist.
The Japanese team hopes to begin drilling by the early 2020s, with 2030 set as a maximum deadline. The site surveys aren’t the only important issue to be addressed — Chikyu will have to test the six-kilometer drill pipe it plans to use, and the Japanese may be hoping to find other nations interested in helping to bankroll the project.
Via Extreme Tech