We know little about the centre of Earth. Geologists believed it had just one core – a hot mass of molten rock surrounded by a rock mantle. This is a ring between the earth's crust and core. The core is 2,900 km below Earth's surface. It has a radius of 3,485 km. Scientists believe there may be a second core. A geophysicist analyzed data from a 560-km-deep earthquake. It showed the possibility of a second core at the bottom of the mantle.

The geophysicist 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." The geophysicist 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."