A new study suggests that the Earth’s core seems to have slowed to a halt.
As humans outside the scientific world, we don’t usually think much about the spinning contents at the center of the Earth, at least not until some sudden movement comes to our attention. However, geoscientists are constantly observing the dynamics of our planet’s interior, which has allowed them to discover that the Earth’s core, which normally rotates within a nearly frictionless molten outer envelope, seems to have slowed to a halt.
How Does the Earth’s Core Rotates?
We have only known for a few decades that the Earth’s inner core rotates relative to the mantle that covers it after Xiadong Song and Paul Richards confirmed it in 1996. Before this, the idea that the Earth’s inner core rotates separately from the rest of the planet was a hypothesis, predicted by an untested model of the magnetic field.
This is why, since then, scientists have been trying to find out how fast or slow the inner core rotates from a distance of 5,100 kilometers. At first, it was thought that the Earth’s core made a complete revolution every 400 years, driven by a pair of electromagnetic poles and balanced by gravitational attraction. However, other scientists theorize that it rotates much more slowly, taking a thousand years or even longer to make a complete revolution. The speed of this rotation, and whether or not it varies, is still a matter of debate today.
The Earth’s Core is Changing
Recently, Xiadong Song again used the same method he and Richards used in 1996 to deduce that the inner core rotates. On that occasion, they tracked seismic wave readings that passed through the inner core, from the South Atlantic to Alaska, over a period from 1967 to 1995.
In the new study, these older data have been reviewed and compared with more recent patterns of nearly identical seismic waves that suggest that the inner core has stalled and may even be reversing.
They have found that since about 2009, trajectories that previously showed significant temporal variation have hardly changed at all as seismic waves passed through the core and out the other side, indicating that any temporal differences had disappeared.
“This globally consistent pattern suggests that the rotation of the inner core has recently stopped,” said geophysicists Yi Yang and Xiadong Song of Peking University in a published paper.
This is not the first time such an event has been recorded, in fact, it is not even the first in recent history. “We show surprising observations indicating that the inner core has almost ceased its rotation in the last decade and may be undergoing a reversal in a multi-decadal oscillation, with another inflection point in the early 1970s,” Yang and Song said.
It also appears that this recent stagnation of the inner core is due to a change in rotation, the solid iron sphere sliding to the other side as part of a seven-decade oscillation. According to calculations, this small imbalance between electromagnetic and gravitational forces would be enough to slow and then reverse the inner core rotation, as observed.
The researchers say that the seven-decade change coincides with other periodic changes observable at the Earth’s surface, in day length and magnetic field, both with a periodicity of six to seven decades. The decade-long patterns in climate observations also appear to line up somewhat.
For Yang and Song, this frequent, slow, and barely perceptible oscillation, which comes and goes every 60 to 70 years, seems to indicate a resonance system between the Earth’s different layers. Because the Earth’s core is believed to be dynamically linked to its outer layers, bound to the outer core by electromagnetic coupling, and bound to the mantle by gravitational forces.
This new study could also help to understand how our planet’s deep processes affect its surface. “These observations demonstrate the existence of dynamic interactions between the Earth’s layers, from the deepest interior to the surface,” Yang and Song conclude.
Story originally published in Spanish in Ecoosfera