Twelve Kilometres Down: The Kola Superdeep Borehole

There is a hole in the ground in northwest Russia, on a flat peninsula that juts into the Barents Sea above the Arctic Circle. It is sealed with a rusted metal disc bolted to a concrete pad. No sign. No fence. No monument. Just a cap on the most ambitious geological drilling project ever completed — the Kola Superdeep Borehole, which reached 12,262 metres into the Earth over the course of twenty-four years, from 1970 to 1994.

This episode follows the Soviet SG-3 project from its quiet start on May 24th, 1970, through the slow years of drilling at a few hundred metres per year, to the discoveries that overturned long-held models of what the continental crust actually looks like — hotter than expected, fractured rather than solid, unexpectedly wet, and carrying the fossilised traces of life at depths where nobody thought life could leave a mark. The hole was capped after funding disappeared and the heat of 180 degrees Celsius at depth defeated the equipment. The depth record, set in 1989, has never been broken.