The Earth’s core is left behind. And we have more and more evidence of this

The planet’s core is moving slower than its crust, and this has been happening since 2010.

If you ask us how fast the Earth rotates, the intuitive answer is obvious: we rotate once every 24 hours. More or less. But if we want to go beyond the intuitive, the answer is a little more complicated. Because we have long known that the interior of our planet does not rotate at the same speed as the surface.

Lagging core. A new study has just shown that the Earth’s core is moving slower than the Earth’s crust, meaning in relative terms it is “receding” when compared to the outer geography of this planet. This finding is not new, but it represents important confirmation of this hypothesis.

It wasn’t always like this. According to the team responsible for the study, it was in 2010 that the Earth’s core slowed down below its daily rotation rate. Moreover, the kernel will continue to slow down depending on the performance results.

Dual core. The Earth’s core consists of two parts. Both are made from a mixture of iron and nickel. What distinguishes them is that the inner core is a solid ball and the outer core is liquid.

An old suspicion. The idea that the core moves slower than the surface of our planet is not new. Two years ago, a similar study (which included part of the team responsible for this new analysis) discovered oscillatory motion in the Earth’s inner core.

They noticed that in the 20th century there were periods when it rotated faster than the surface (superrotation), and in others it slowed down (subrotation). The new study adds new evidence to what we know about the current relative motion of the nucleus.

“When we discovered a dozen new observations pointing to the same pattern, the result was inevitable. The inner core slowed for the first time in decades. Other scientists have recently advocated similar and different models, but our latest study provides the most compelling solution yet,” explained John Vidale, co-author of the current study and the study published in 2022, in a press release.

Repeated earthquakes and nuclear tests. The observations on which these studies are based are based on how seismic waves propagate in the Earth’s interior, since in practice this is the only way to “see” elements of our planet hidden thousands of kilometers below its surface. . The seismic signals used are distinguished by origin: natural (earthquakes) and artificial (atomic tests).

More specifically, the team used “repeat” earthquakes, which are “seismic events that occur in the same location and produce identical seismograms,” the team explains. They counted more than 120 such earthquakes that occurred in the Sandwich Islands between 1991 and 2023.

Data to which they also added new data on Soviet nuclear tests conducted in the 1970s and other French and American nuclear tests already included in previous studies. A new study was recently published in the journal Nature.

What causes this slowdown? According to Vidale himself, this slowdown will be caused by currents in the liquid iron that makes up the Earth’s outer core – the same movement that generates our planet’s magnetic field. This movement, in turn, is caused by gravitational interactions between the densest regions of the Earth’s mantle.

Don’t adjust the clock. As far as we know, in practice the consequences of these imbalances there are negligible. The slowing of the core could slow the rotation speed of the planet as a whole, lengthening the day. However, the difference will be so small that it is barely noticeable: an order of magnitude in thousandths of a second.

In Hatak | The theory that the Earth’s core is rusting (and its unpredictable consequences)

Image | A.shteivi, CC BY-SA 4.0