Supercooling of Earth’s inner core may finally reveal its true age

Earth’s inner core, made of solid iron and nickel, lies more than 3,200 miles (5,100 kilometers) below the surface. Despite its crucial role in shaping Earth’s conditions and generating its magnetic field, the core’s age has remained a mystery. Now, thanks to advances in mineral physics, scientists are closer to understanding how and when the core formed. The solid core is vital to maintaining Earth’s magnetic field, which protects us from harmful solar radiation and keeps the planet habitable for billions of years.

Formation and freezing process of the inner core

The inner core, once molten, solidifies as Earth cools. This cooling process causes the iron-rich liquid surrounding the core to freeze, causing the inner core to expand outward, though temperatures inside the core remain scorching, at over 5,000 K (about 4,726 °C). The freezing of the iron releases lighter elements such as oxygen and carbon, creating a buoyant liquid that rises into the outer core and produces electric currents. These currents drive Earth’s magnetic field, which is responsible for phenomena such as the Northern Lights.

Supercooling and the age of the core

Geophysicists use thermal models to study The Earth’s magnetic history. These models have revealed that supercooling, where a liquid cools below its freezing point without solidifying, could explain the formation of the core. Recent studies suggest that iron in the core may have to be supercooled by up to 1,000K before it freezes. However, this degree of cooling implies that the core could be much younger, between 500 and 1,000 million years old, than previously thought. Current evidence suggests that the core may have undergone less than 400K of supercooling.

The age of the Earth’s inner core continues to be a subject of intense study, with scientists investigating the possibility that the core could be younger than previously estimated due to this supercooling phenomenon. Understanding this could change our understanding of Earth’s magnetic history.