Earth’s core rotates slower than thought
3 Mar 2011 by Evoluted New Media
The Earth’s core is moving at one degree every million years, not one degree each year as scientists previously believed suggests new research.
The Earth’s core is moving at one degree every million years, not one degree each year as scientists previously believed suggests new research.
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The Earth’s core isn’t moving as fast as scientists thought |
Previous studies suggested the Earth’s core rotates faster than the rest of the planet – thought to be one degree every year – but researchers from University of Cambridge found these estimates were incorrect. Their research suggests the core actually moves at approximately 1 degree every million years.
The inner core grows very slowly over time as material from the fluid outer core solidifies onto its surface – during this process, an east-west hemispherical difference in velocity is frozen into the inner core’s structure.
“The faster rotation rates are incompatible with the observed hemispheres in the inner core because it would not allow enough time for the differences to freeze into the structure,” said Lauren Waszek, first author and PhD student from the department of earth sciences.
“This has previously been a major problem, as the two properties cannot coexist. However, we derived the rotation rates from the evolution of the hemispherical structure, and thus our study is the first in which the hemispheres and rotation are inherently compatible.”
Researchers compared the travel time of seismic body waves to waves which reflect from the inner core surface – the difference between them provided scientists with the velocity structure of the uppermost 90km of the inner core.
This was reconciled with the differences in velocity for the east and west hemispheres of the inner core. The researchers observed the east and west hemispherical differences in velocity, and then constrained the two boundaries which separate the hemispheres. They found they both shifted consistently eastward with depth.
Since the inner core grows over time, the deep structure is older, and the shift in the boundaries between the two hemispheres results in the inner core rotating with time. The rotation rate is calculated from the shift of the boundaries and the growth rate of the inner core.
“This result is the first observation of such a slow inner core rotation rate,” Waszek said.” It therefore provides a confirmed value which can now be used in simulations to model the convection of the Earth’s fluid outer core, giving us additional insight into the evolution of our magnetic field.”
