Kola Superdeep

On this day in 1970, Russian scientists began drilling on the Kola Peninsula, with the intention to penetrate the Earth's crust as deeply as possible. The deepest borehole reached a depth of over 40,200 feet in 1989. Due to the 180°C / 355° F temperature at that depth, further drilling was considered unfeasible and the project focus switched to analysis of the core samples that had been retrieved. The project was finally shut down in 2005.