The iron-rich core at the centre of our planet has been a crucial part of Earth's evolution. The core not only powers the magnetic field which shields our atmosphere and oceans from solar radiation, it also influences plate tectonics which have continually reshaped the continents.

But despite its importance, many of the most fundamental properties of the core are unknown. We do not know exactly how hot the core is, what it is made of or when it began to freeze.

Fortunately, a recent discovery by me and my colleagues brings us much closer to answering all three of these mysteries.

We know the temperature of Earth's inner core is very roughly about 5,000 Kelvin (K) (4,727°C). It was once liquid, but has cooled and become solid over time, expanding outwards in the process. As it cools,

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