We know little about the centre of Earth. Geologists believed our planet had just one core – a hot mass of molten rock and gas surrounded by a rock mantle. The mantle is a ring between the earth's crust and core. The core is 2,900 kilometres below Earth's surface. It has a radius of around 3,485 kilometres. Scientists have found that there may be a second core. Geophysicist Sunyoung Park analyzed data from a 560-km-deep earthquake. Her calculations showed the possibility of a second core. It consists of a layer of fluid rock at the bottom of the mantle.

Dr Park studied the earthquake and explained what intrigued her about Earth's core. She said: "There's still a lot we don't know about it. There's a lot more we can learn by using deep earthquakes." Park explained the importance of understanding more about the core. She said: "We want to know exactly how fast the mantle flows because that influences the evolution of the entire Earth. It affects how much heat the planet retains for how long….Our current understanding is very limited and includes a lot of assumptions."