The Earth's core is slowing down and we don't know the cause

A new study has confirmed how the Earth's core is slowing down, but the real cause is not yet known

by Lorenzo Ciotti
The Earth's core is slowing down and we don't know the cause
© Wikimedia Commons

The Earth's inner core is slowing down, according to a University of Southern California study published in the journal Nature. Data collected by scientists over the last 20 years shows that the rotation speed began to reduce starting in 2010, making the core slower than the Earth's surface. The authors of the study used information from 121 earthquakes that recurred in the South Sandwich Islands, in the Atlantic Ocean, between 1991 and 2023, as well as that obtained thanks to Soviet, French and American nuclear tests carried out over the years seventy.

According to the researchers, this change in rotation could be due to the mixing of the outer core and the gravitational attraction that is established with the overlying rocky mantle. The study hypothesizes that this change could alter the length of the day on the order of fractions of a second, an infinitesimal change that would be difficult to notice.

Earths core
Earths core© Wikimedia Commons

John Vidale, coordinator of the study, explained: "When I first saw that the seismograms suggested a slowdown, I was perplexed. But when other observations also signaled the same pattern, the conclusion was inevitable: the core domestic slowed down for the first time in many decades."

The Earth's core is characterized by a high density and is separated from the mantle by a discontinuity, called Gutenberg, located approximately 2900 km from the surface. The nucleus, therefore, has a radius of approximately 3500 km and, based on the phase of the components that constitute it, is further divided into two concentric shells. The external, liquid core is mainly composed of iron (20%) and nickel and is characterized by a temperature of 3000 °C, a density of 9.3 g/cm³ and a pressure of 140 GPa; the convective currents in the liquid outer core would, according to some theories, be the cause of the origin of the Earth's geomagnetic field, based on the geodynamo model.

The internal core is instead viscous, composed almost exclusively of iron, with a radius of approximately 1250 km, has a temperature around 5400 °C/6000 °C, a density of 13 g/cm³ and a pressure of 330-360 GPa. These limiting conditions suggest that iron is in a crystalline state. Although the temperature of the inner core is higher than the outer one, it is viscous because the pressure is higher and this leads to a notable increase in the melting point of the iron. But if it could hypothetically be punctured, it would be liquid. According to recent studies, the core temperature is mostly produced by the spontaneous decay of radioactive elements such as uranium, thorium and potassium.