What's At The Centre Of The Earth?

We live on the surface of a dense, rocky ball, but science has allowed us to peer deep within its core

- Brian Clegg

When the pioneering science fiction writer Jules Verne wrote Journey To The Centre Of The Earth in 1864, he probably knew that his plot was pure fantasy. Verne’s characters Otto, Axel and their guide Hans, only made it a few miles down, but the idea that anyone could even contemplate travelling to the Earth’s core had been dismissed before Victorian times.

Even today, the furthest we’ve ever drilled into the Earth is around 12km, while the distance to the centre is over 500 times further, at 6,370km. So how do we know what lies beneath? Figuring out what’s at the heart of our planet has been a magnificent scientific puzzle.

Living on a ball 

The idea of the Earth having a meaningful centre goes hand-in-hand with the planet being shaped like a ball, and we’ve known that we don’t live on a disc for a long time. It’s a myth that medieval folk thought the Earth was flat – this actually came from a mix of Victorian anti-religious propaganda, and a misinterpretation of the stylised maps of the period. It was over 2,200 years ago that the Greek polymath Eratosthenes made the first measurement of the distance around the Earth’s sphere, and it’s been clear ever since that it must have a centre.