A new study confirms that the Earth’s inner core has been rotating more slowly than usual since 2010. The mysterious «reverse motion» may also lead to a change in the overall rotation of the planet, which could result in an increase in the length of the day.
The Earth’s inner core is composed of solid iron and nickel, is about the size of the Moon, and is located 4,800 km below the surface. It is surrounded by an outer core — an ultra-hot layer of molten metals surrounded by a harder mantle of molten rock and an outer crust. The inner core rotates at a different speed than the mantle and crust because of the viscosity of the outer core.
Ever since scientists began mapping the Earth’s interior about 40 years ago with detailed records of seismic activity, the inner core has rotated slightly faster than the mantle and crust. But in a new study published in the journal Natureresearchers from the University of Southern California have found that since 2010, the inner core has been slowing down and now rotates slightly slower than the outer layers of our planet.
If the rotation of the inner core continues to slow down, its gravitational pull may cause the outer layers of our planet to rotate slightly slower, changing the length of the day. However, the change will be small, on the order of thousandths of a second. Clocks and calendars will not have to be changed, especially if it is only a temporary change.
The researchers analyzed data from more than 100 recurrent earthquakes along the tectonic plate boundary in the South Sandwich Islands in the South Atlantic between 1991 and 2023. The earthquake data allowed the scientists to map the position of the core relative to the mantle, and by comparing these measurements, the team was able to see how the rotation rate of the inner core changes over time.
It’s not clear why the inner core is turning back, but it’s likely caused by either «churning of the outer core by the liquid iron that surrounds it» or «gravitational pull from dense regions of the rocky mantle», the study says. It is also unclear how often the rotation changes. It is possible that the rotation of the inner core is constantly accelerating and decelerating, but these changes occur over decades or longer. Therefore, more information is needed to draw conclusions about long-term trends. The study authors will continue to analyze seismic data to learn more.
This is not the first time scientists have suggested that the Earth’s inner core is slowing down. Similar results were recently obtained by scientists Peking University. This phenomenon, known as «backward motion», has been discussed for about a decade, but it is very difficult to prove.
Source: LiveScience