For decades, scientists believed the Earth’s innermost layer, the solid iron sphere at the center of our planet, was about the same age as Earth itself — around 4.5 billion years old. But new research published in the journal Nature Geoscience suggests that Earth’s inner core is significantly older — closer to 1 billion years old.

The discovery, which overturns a long-held assumption about Earth’s geologic history, has implications for our understanding of the planet’s formation and evolution.

The study was led by researchers at the University of California, Berkeley. They used a technique called seismic tomography to create a 3-D image of Earth’s inner core. Seismic tomography works by sending seismic waves, which are vibrations that travel through the Earth, into the planet and then recording how those waves bounce back and forth between the inner core and the surface.

By analyzing the seismic waves, the researchers were able to determine that the inner core is made up of two layers: a younger, outer layer about 500 million years old, and an older, inner layer about 1 billion years old.

The discovery that the Earth’s inner core is older than previously thought has important implications for our understanding of the planet’s formation and evolution.

It suggests that the Earth’s core formed much earlier than previously thought, and that the Earth’s interior has undergone more complex changes over time than scientists had previously realized.