A new and surprising study fresh in ‘Nature Geoscience’ By scientists from the University of Southern California (USC) has revealed that the internal nucleus of the Earth is not exactly as expected, but is subject to a series of … Unexpected structural changes on its surface, which challenges the traditional idea that it is a solid and homogeneous sphere. The finding, which focuses on the ‘almost surface’ of the internal nucleus, opens a new chapter in the understanding of the internal dynamics that act on our planet and its impact on phenomena such as the duration of the day or the intensity of the Earth’s magnetic field.
For decades, the investigation of the planet’s internal nucleus has focused on the analysis of its rotation. Scientists sought to understand how this solid iron sphere revolves, located about 4,800 kilometers deep, and how that rotation affects the populated surface of our world. In that line, the team of researchers led by John Vidale, professor of Earth Sciences at the USC, did not intend to study the physical nature of the internal nucleus directly, but rather understand the reasons why their rotation is slowing down. But what they found was much more surprising.
“What we end up discovering,” says Vidale, “is the evidence that the ‘almost surface’ of the earth’s internal nucleus is experiencing structural changes.”
Mainly composed of solid iron, the internal nucleus is ‘anchored’ by gravity inside the external nucleus, an iron layer and liquid nickel in rapid rotation. Until now, the scientific community considered that the internal nucleus was a relatively uniform solid sphere. But the new study challenges this vision.
To try to understand why the internal nucleus is slowing down, Vidale and his colleagues analyzed seismic data accumulated in numerous previous studies. “While analyzing multi -decades seismic records,” explains the researcher, “a set of seismic wave data, curiously stood out from the rest. Later, I realized that what I was observing was the evidence that the internal nucleus is not solid ».
Written in seismic waves
The study used data of seismic wave forms of 121 earthquakes in 42 locations near the South Sandwich Islands in Antarctica, which occurred between 1991 and 2024. These earthquakes, although imperceptible to humans, generate seismic waves that travel through the Land and provide valuable information about their internal structure. The researchers analyzed these waveforms in receiving stations located near Fairbanks, Alaska, and Yellowknife, Canada.
It was in this last station where a specific data set showed unusual properties, never before observed in any other analysis. “At first,” says Vidale, “the data set confused me.” In fact, it was not until his team improved the resolution technique that became clear that the seismic waveforms represented a new and unknown physical activity of the internal nucleus.
To understand it better, imagine that we try to ‘see’ the interior of a melon using sound waves. If the melon were completely homogeneous, the sound waves will cross it predictably and constantly. But if there are areas with different density or texture, the sound waves will disperse and reflect differently in each of those areas, revealing the internal structure of the melon. Similarly, seismic waves revealed to researchers complexity of the internal nucleus.
A deformed internal nucleus
The new activity detected is best explained as temporary changes in the form of the internal nucleus. And the new study, in effect, indicates that its ‘almost surface’ can be experiencing a viscous deformation, changing its forms in the superficial zone as the honey would do. In other words, the ‘almost surface’ of the internal nucleus, although solid, behaves like a highly viscous material, capable of slowly deforming under pressure.
According to the study, the clearest cause of this structural change is the interaction between the internal and external nuclei. “It is known that the molten external nucleus is turbulent,” explains vidale, “but it had never been observed that its turbulence disturbs its neighbor, the internal nucleus, in a human time scale. What we are seeing in this study for the first time is, probably, how the external nucleus disturbs the internal nucleus. » Something similar to what would happen if the agitation of boiling water in a pot was affecting the shape of a solid object that floats on its surface, although at a much slower time scale.
The unexpected finding opens a range of possibilities to reveal previously hidden dynamics in the depths of the earth’s core, and can lead to a better understanding of the thermal and magnetic field of the Earth, which protects us from the harmful solar radiation and is generated, Precisely, thanks to the interaction of the external and internal nuclei.
Therefore, understanding in detail how these two layers interact is crucial to understand the evolution of the magnetic field and other geophysical phenomena. In that sense, Vidale’s research and his team represents a great step forward and shows that even the deepest and most apparently solid regions of the earth can be surprisingly dynamic and changing.
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