The Earth’s inner core appears to be slowing its rotation
The provocative findings come after years of research and deep scientific controversies about the core and how it affects some fundamental aspects of our planet, including the length of the day and fluctuations in Earth’s magnetic field.
Three thousand miles below the surface, a hot ball of solid iron floats inside a liquid outer core. Geologists believe that energy from the inner core causes the fluid in the outer core to move, generating electric currents that in turn generate a magnetic field that surrounds the planet. This magnetic shielding protects organisms on the surface from the most harmful cosmic radiation.
Don’t panic. The slowdown of the core is not the beginning of the end of time. The same thing seems to have happened in the late 1960s and early 1970s, with the study authors at Peking University in China They suggest that it may represent a 70-year cycle of acceleration and deceleration of the core’s rotation.
But while other experts have praised the rigor of the analysis, the study will intensify a fierce scientific debate about what is what Mysterious metal ball At the center of the Earth up to.
“It’s only controversial because we can’t detect it,” said John Vidal, a geophysicist at the University of Southern California. “It’s probably benign, but we don’t want to have things that we don’t understand deep down.”
The new study was led by Xiaodong Song, a geologist at Peking University whose work in 1996 first led to the introduction of Evidence that the kernel was doing its own thing. Buried beneath the mantle and crust, the core is too deep to visualize directly, but scientists can use seismic waves generated by earthquakes to infer what’s going on in the bowels of the planet. Seismic waves travel at different speeds depending on the density and temperature of the rocks, so they act as a kind of x-ray to the Earth.
The study examined seismic waves that traveled from the earthquake sites to sensors on the other side of the planet, passing through the core on the way. By comparing waves from similar earthquakes that hit the same spot over the years, scientists were able to look for and analyze time periods and perturbations in the waves that gave them indirect information about the core — or as some scientists call it, the planet within our planet.
“The inner core is the deepest layer of the Earth, and its relative rotation is one of the most interesting and challenging problems in geoscience,” Song said in an email.
The behavior of the nucleus may be related to subtle changes in the length of the day, although the exact details are a matter of debate. The length of a day has been growing by milliseconds over centuries due to other forces, including the moon’s pull on Earth. But super-accurate atomic clocks have measured mysterious fluctuations.
Song and colleagues argue that these differences may be consistent with changes in the spin of the nucleus. The new paper finds that when they remove the expected fluctuations in day length due to the moon’s tidal forces, there are changes that appear to follow the 70-year oscillations in the rotation of the inner core.
Paul Richards, seismologist Columbia University’s Lamont-Doherty Earth Observatory worked with Song to provide the first evidence that the core was spinning faster than the rest. Universe.
“Most of us have assumed that the inner core rotates at a constant rate that is slightly different from Earth’s,” Richards said. The evidence is piling up, and this paper shows the evidence [faster] Alternation was strong before about 2009, and basically dies out in subsequent years.”
However, he cautioned that things quickly become speculative when trying to understand the effect of substance on other phenomena. That’s because the behavior of the substance itself remains a contentious question – with simplifying assumptions increasingly refined over the years.
For example, there is evidence to support other ideas about how Earth’s core should behave. Vidale of USC has studied seismic waves generated by Nuclear explosionsand favors a shorter six-year oscillation of the nucleus turnover rate.
Lianxing Wen, a seismologist at Stony Brook University, completely rejects the idea that the core rotates independently. Arguing that changes over time to inner surface of the heart It is a more plausible interpretation of seismic data.
“This study misinterprets seismic signals that are caused by latitudinal changes in the Earth’s inner surface,” Wen said in an email. He added that the idea that the inner core rotates independently of the surface “offers an inconsistent interpretation of the seismic data even if we assume they are correct.”
What geoscientists agree on is that as more data accumulates, many of the initial ideas about the core’s behavior have become more complex.
“Ultimately, I don’t think complexity is an issue in geoscience,” Elizabeth Day, a geophysicist at Imperial College London, said in an email. “We know that the surface of our planet is complex… so it’s logical to assume that deep inside the Earth is complex too! To say for sure how the inner core rotates relative to the outer layers of the planet, we’ll need to keep collecting as much data as we can.”
The stakes of this scientific debate are great in part because at its core is a mystery that lurks, unsolved, so close to home.
“It’s not something that’s going to affect potato prices tomorrow,” Richards said. But the debate speaks to deeper questions about Earth’s formation and how its inner layers support life on its surface, something that could aid in studies of habitability on rocky planets orbiting other stars.
“When you think about … what our planet is made of and what its history is,” Richards said, “a deep understanding of the inner core brings you to ‘How did all these subdivisions of planet Earth evolve?'” “