Russian scientists have drilled into the vast, dark and never-before-touched Lake Vostok 2.2 miles below the surface of Antarctica, according to a source quoted Monday by Ria Novosti, a state-run Russian news agency.

The subglacial lake, the world’s third-largest lake by volume, is 20 million years old and could be contaminated by the kerosene, Freon and other materials being used in the drilling.

Also see: “Scientists close to entering Vostok, Antarctica’s biggest subglacial lake”