Through the Earth’s Mantle—and 800 Miles of Dirt and Rock

This isn’t, strictly speaking, a post about erosion, but we hear so frequently about problems with abandoned mining sites—degraded or contaminated soils, expensive remediation efforts—that I want to pass along a story about one that’s doing well in its afterlife. The Homestake Gold Mine in South Dakota closed in 2001. Now the site is a player in potentially unlocking the secrets of the universe.

The mine is being transformed into a laboratory—the Sanford Underground Research Facility—that will be an essential part of the $1 billion Deep Underground Neutrino Experiment. Funded by the US Department of Energy, the European Organization for Nuclear Research (CERN), and dozens of other institutions from around the world, the experiment’s goal is to help scientists understand the role neutrinos—the subatomic particles produced when radioactive elements decay—might have played in the evolution of the universe. As this article notes, the more than 1,000 scientists involved in the project ultimately hope to learn “why matter exists.”

The lab will feature three mile-deep chambers containing 70,000 tons of liquid argon; excavation and construction of these chambers began in late July. A beam of neutrinos will eventually be fired toward the site from Fermilab in Batavia, IL, passing through the Earth’s mantle—about 800 miles of dirt and rock—in just four milliseconds before hitting the liquid-filled neutrino detectors. Scientists will be studying how the particles interact with the argon and what changes they undergo as they pass through the mantle. You can read more about the experiment here.

Work began on the lab in 2012, and the first beam won’t actually be fired for about a decade (the equipment to fire the neutrinos has yet to be built at the Illinois end). In the meantime, though, the project is a boon for the small South Dakota city of Lead (population about 3,100), which was settled in the 1870s and has been home ever since to employees of the Homestake Mining Company, and apparently to few others. Maintaining and outfitting the lab runs to about $20 million a year.