Scientists in China have announced that they have confirmed a link between a signal recorded 8.5 years ago and a ‘wobble’ in the Earth’s core.
Scientists in China say they have uncovered a big secret deep inside the Earth, confirming that the inner core shakes in a predictable rhythm that repeats every 8.5 years.
The finding confirms earlier measurements made by the team in 2018 and challenges earlier assumptions about the relationship between the Earth’s layers and how their movement influences phenomena such as changes in the length of days, the research team said in a report by Mirjam Guesgen and translated into Turkish by Tarkan Tufan. The research paper is published in the journal Nature Communications.
Understanding the properties of the solid iron and nickel fragment called the ‘inner core’, which floats inside a layer of liquid metal called the ‘outer core’, is much more difficult than imaginary trips to the center of the Earth. Much of scientists’ knowledge of the inner core and its motions has come from waves propagating across the planet, caused by violent earthquakes or nuclear bomb tests. But understanding the inner core and its motions is crucial to unlocking the secrets of Earth’s structure, magnetic field and earthquakes.
A discovery that challenges the dominant understanding
In 2018, geophysicist Hao Ding and colleagues, co-authors of the newly published study, examined how the movement of Earth’s poles subtly changes over time. The team found that there is a pattern or harmonic ‘signal’ that repeats every 8.5 years, and in the new study they confirmed this using measurements of how the length of days changes over time. This pattern, they explain in the new paper, is the result of wobbling in the Earth’s inner core.
Their investigation also led them to conclude that the core should be tilted by about 17 degrees compared to the Earth’s mantle, or crust. This result seems to contradict the prevailing idea that the tilt is much larger and that the rotation of the core matches that of the mantle. It also suggests that the core is not perfectly spherical, but rather egg-shaped and denser in the northwestern part.
“These deviations provide us with a valuable framework for the 3-D density model of the mantle and question the assumptions of fluidity-polar compression in the core, highlighting possible deviations from the perfect spherical form calculated using conventional theories,” Ding said in a press release.
An element that triggers various changes
And all these tilts and wobbles create a ripple effect. The wobble pattern in the Earth’s core drives the oddities in the Earth’s overall rotation and the length of days, and may provide an explanation for other phenomena such as the Earth’s changing magnetic field, the study authors say. “The static [constant] tilt could, among other things, lead to a certain change in the shape of the liquid core, causing a variation in the motion of the fluids and a corresponding change in the geomagnetic field,” says Ding.
However, the new research is not the only way to explain phenomena like this. Different theories suggest that a geophysical struggle between the Earth’s magnetic field and the mantle’s gravitational field causes the inner core to rotate, first backwards and then forwards, roughly every 70 years. Or this phenomenon is due to the fact that the surface of the core has peaks and valleys that change rather than being static and smooth.
John Vidale, a seismologist at the University of Southern California who was not involved in the latest study, said in an earlier statement: “I don’t think there are many things in the earth sciences that are as poorly understood as the movement of the inner core. Trying to understand precisely what’s happening has been an ongoing struggle for a long time.”
While some uncertainties remain, the latest research is a step forward in clarifying some of these debates. “We aim to study the cyclic oscillation and variable rotation of the Earth’s core in more detail, thereby clarifying these conceptual theories, which can be disparate and difficult to reconcile,” Ding said.