For decades, scientists have believed that Earth's inner core is about 1 billion years old. This age estimate is based on the time it would have taken for the core to cool and solidify from the surrounding liquid outer core.

However, a new study published in the journal Nature suggests that the inner core may be much older. Researchers from the University of California, Berkeley, used a new type of seismic wave analysis to study the structure of the inner core. They found that the core is not as uniform as previously thought; instead, it contains two distinct layers.

The outer layer of the inner core is made up of iron and nickel, while the inner layer is made up of a mixture of iron, nickel, and silicon. The researchers believe that the two layers formed at different times, with the inner layer being older than the outer layer.

The new findings suggest that the inner core may be up to 4.5 billion years old, the same age as the Earth itself. This would make the inner core one of the oldest objects in the solar system.

The study also sheds light on the formation of the Earth's core. The researchers believe that the core originally formed as a solid ball of iron and nickel. As the Earth heated up, the core began to melt, forming a liquid outer core and solid inner core. Over time, the inner core grew as more and more iron and nickel crystallized from the liquid outer core.

The new findings help to improve our understanding of the Earth's interior and its evolution over time.