In the 1970s and 1980s, scientists in Russia managed to dig a hole more than 12,000 metres deep.

It was called the Kola Superdeep Borehole.

They wanted to achieve a world record and learn more about the Earth's crust.

Rachel Naylor speaks to Prof David Smythe, a geophysicist who worked there for four months.

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(Photo: The site of the Kola Superdeep Borehole in the 1990s. Credit: David Smythe)