By Ron Cowen
On an early summer morning in northern Minnesota, a crew of about a dozen waits by the top of mine shaft No. 8. Donning hard hats, the engineers and physicists pile into a creaky, double-decker elevator cage. It is pitch black for most of the three-minute descent. Ears pop, the cage floor vibrates and a giant motor dating from 1925 thunders overhead.
When the cage door slides open, the team is 713 meters below the surface. Directly ahead lies a maze of tunnels — an abandoned mine where laborers once extracted iron ore of uncommon purity. But the scientific crew takes a U-turn into a huge and unexpectedly spacious two-room cavern known as the Soudan Underground Laboratory.
The workers have journeyed deep into the Earth to plumb the darkest depths of the cosmos, hunting for the missing material believed to account for 83 percent of the universe’s mass.