What’s the deepest hole we’ve ever dug?

The record for subsurface drilling is held by the Kola Superdeep Borehole in north-west Russia. The scientific project reached 12,262 metres (40,230 feet) in 1989 before 180-degree -Celsius (356-degree-Fahrenheit) temperatures forced it to stop.

The trouble with drilling to Earth’s core is not just the tough rock, crystal and eventually molten metal you’ll encounter, but the rapidly increasing pressure, friction and heat. At around 1.5 million metres (4.9 million feet), temperatures would exceed 300 degrees Celsius (572 degrees Fahrenheit) – more than any drill-bit can cope with. Even then, we would still be over 4,500 kilometres (2,800 miles) from the inner core.