Kola Superdeep Borehole

The deepest geothermal well built to this point is the Kola Superdeep Borehole. It extends more than seven miles into the earth at its deepest point and was used for geological research until the early 1990s.

The most intriguing discovery made by the Kola borehole researchers is undoubtedly the detection of biological activity in rocks more than two billion years old. The clearest evidence of life came in the form of microscopic fossils: the preserved remains of twenty-four species of single-cell marine plants, otherwise known as plankton. Usually, fossils can be found in limestone and silica deposits, but these “microfossils” were encased in organic compounds that remained surprisingly intact despite the extreme pressures and temperatures of the surrounding rock.

While data produced by the Kola drilling project continues to be analyzed, the drilling itself was forced to stop in the early 1990s when unexpectedly high temperatures were encountered. While the temperature gradient conformed to predictions down to a depth of about 10,000 feet, temperatures after this point increased at a higher rate until they reached 180 °C (or 356 °F) at the bottom of the hole. This was a drastic difference from the expected 100 °C (212 °F). Also unexpected was a decrease in rock density after the first 14,800 feet. Beyond this point, the rock had greater porosity and permeability which, paired with the high temperatures, caused the rock to behave more like a plastic than a solid and made drilling near impossible.

A repository of the many core samples can be found in the nickel-mining town of Zapolyarny, about ten kilometers south of the hole. For its ambitious mission and its contributions to geology and biology, the Kola Superdeep Borehole remains one of the most important relics of Soviet-era science.

READ MORE