The Earth's core has stopped, but everything remains (almost) the same

Recently, a study has been published in which it is said that the Earth’s core has suffered a break and that this event has an influence on different aspects of the planet, such as the magnetic field or the climate.

In the wake of this publication, some voices have emerged suggesting exaggerated and catastrophic consequences. It is important to analyze these news with a critical vision. Without minimizing the great impact of scientific discoveries on the functioning of our planet —even with so many mysteries— do not fall into simplicity or drama.

To understand this news, we must first know the internal structure of our planet, which is made up of different layers. In the center is the inner core of the Earth, a solid sphere of iron and nickel with a radius of 1,220 km. It is surrounded by a 2,260 km thick layer of similar composition, but in a molten state, the outer core.

The first thing to make clear is that the Earth’s core has not stopped. Our planet with all its layers is rotating in such a way that it takes about 24 hours to complete one revolution.

The convection movements in this fluid layer, together with the terrestrial rotation, generate the magnetic field that protects our planet from particles that arrive from the Sun and from space. Around the core we find the mantle, about 2,900 km thick, and above this, the earth’s crust on which we live, only 10 to 50 km thick.

The first thing to make clear is that the kernel has not stopped. The Earth with all its layers is rotating in such a way that it takes approximately 24 hours to complete one revolution.

Until now it was thought that the inner core rotated a little faster than the mantle and crust—this is called super-rotation—so that it was moving forward by about a tenth of a degree each year.

According to this new study, the Earth’s core would have slowed down to the same rotation speed as the outermost layers or even slightly less. These relative speed differences are very small.

The example of the car on the highway

Let’s imagine, as an example, that we are going on the highway at 120 km/h and another car passes us at 121 km/h. Through the window we will see that he is overtaking us little by little. If now the other vehicle brakes and goes to 120 km/h we will see it “immobile” next to our car. It keeps moving though, just like us.

To conclude that the core now rotates more slowly, the researchers selected earthquakes originating in the South Sandwich Islands, in the southern part of the Atlantic Ocean. And they studied the signal recorded at an observatory in Alaska, almost on the other side of the planet.

In the same way, the core would have slowed down and, now, rotating at the same speed as the mantle and crust, from the Earth’s surface we would see it stopped.

In this way they were able to analyze the time it took for the waves that had crossed the Earth’s core to arrive, always following the same trajectories. They observed that the waves took different times to cross the core at different times.

Different areas of the nucleus can have different properties, which means that waves take longer to cross some areas than others. So they concluded that if the travel time of the waves changed over the years, it’s because the inner core was getting ahead of the crust.

In other words, if for waves emitted and recorded at the same points on the surface we obtain different results depending on the time. It means that the waves are going through different areas of the nucleus, that is, it is rotating at a different speed than the surface of the Earth.

If for seismic waves emitted and recorded at the same points on the surface we obtain different results depending on the time, it means that they go through different areas of the core, that is, it is rotating at a different speed.

However, since 2009 the waves have always taken the same time to cross the core. This means that the nucleus is now stationary relative to the surface (it rotates at the same speed). The same results were obtained when the study was extended to earthquakes generated in other parts of the planet, supporting the previous conclusions.

This slight shift in core rotation isn’t the first time it’s happened. The data shows another similar event in the 1970s. This suggests that the phenomenon repeats itself with a periodicity of about seven decades.