Kola Superdeep Borehole
A Soviet research hole sunk from 1970 and given up at 12,262 metres. Nothing has gone deeper straight down since: at that depth the rock is 180°C and stops behaving like rock.
The crust under our feet had only ever been read at a distance. On 24 May 1970 the Soviet Union began drilling into the Baltic Shield — five holes, 23 centimetres across. The deepest stopped at 12,262 metres in 1989, about a third of the way through crust roughly 35 kilometres thick. Work halted in 1992 at 180°C, hot enough to deform bits and pipe and to leave the rock itself behaving like something plastic. Funding ran out in 1995.
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