Scientists say they know more information about what lies at the very centre of the Earth.
Research from China and the US suggests that the innermost core of our planet has another, separate section at its centre.
The team think that the structure of the iron crystals there are different from those found in the outer part of the inner core.
The findings are reported in the journal Nature Geoscience.
Without being able to drill into the heart of the Earth, its make-up has been a mystery.
So instead, scientists use echoes generated by earthquakes to study the core, studying how they change as they travel through the different layers of our planet.
Prof Song and his colleagues in China say this data suggests that the Earth's inner core - a solid region that is about the size of the Moon - is made up of two parts.
He said: "The fact we are discovering different structures at different regions of the inner core can tell us something about the very long history of the Earth."