The Earth slows down, but everything remains (almost) the same

A study was recently 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 this news with a critical vision and, without minimizing the great impact of scientific discoveries on the functioning of our planet (even with so many mysteries), not fall into simplicity or drama.

To understand this news, we must first know the internal structure of our planet. The Earth is made up of different layers. In the center is the inner core, a solid sphere of iron and nickel with a radius of 1,220 kilometers. It is surrounded by a 2,260-kilometer-thick layer of similar composition, but in a molten state, the outer core. 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 kilometers thick, and, above it, the earth’s crust on which we live, only 10 to 50 kilometers 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 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. Consider, 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 speeds up to 120 km/h, we will see it “immobile” next to our car, although it continues to move, just like us. 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.

The Earth seen from the space. (Photo: NASA)

To conclude that the core is now rotating more slowly, the researchers selected earthquakes originating in the South Sandwich Islands, in the southern part of the Atlantic Ocean, and studied the signal recorded at an observatory in Alaska, almost on the other side of the planet. 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 is because the nucleus internal was getting ahead of the cortex. 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 nucleus. Land.

However, since 2009 the waves have always taken the same time to cross the nucleus. 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 several decades. Interestingly, this same frequency also appears in other geophysical observables, such as the geomagnetic field, the length of the day or the weather, which suggests that they may be related. It is currently thought that this phenomenon of periodic variation in the rotation of the core is due, on the one hand, to the electromagnetic interaction between the inner and outer core that tends to accelerate the inner core and, on the other, to gravitational coupling with the mantle. , which forces him to return to rhythm.

In short, does the study say that the core stopped dead in 2009 and is going to start spinning in the opposite direction? No, it’s just changed its velocity relative to the crust. Throughout history, the magnetic field has already been reversed on many occasions. Does this slowdown of the nucleus suggest an imminent reversal of the poles or that the magnetic field may disappear? No, the nucleus continues to spin and the magnetic field will continue to be generated. Will this phenomenon have implications for the climate? The study suggests that there might be some relationship, but that the origin of the multidecadal variations in climate is not yet fully understood. Furthermore, it does not seem likely that such small changes in the rotation of the nucleus could have really appreciable effects.

As we can see, the dynamics of the Earth is a system of great complexity and there are a multitude of interconnected factors that determine the characteristics and evolution of our planet. The long history of Earth compared to our study of it makes understanding its evolution a great challenge. Discoveries like this are a sample of the efforts of science to understand better and better how the planet where we live works. (Source: Alberto Molina Cardín / Marina Puente Borque / Pablo Rivera Pérez / Institute of Geosciences (IGEO-CSIC-UCM))