Earth's core is rotating faster than its surface

[HydrogenBond]

Moderation note: the first 3 posts of this thread were moved from Cold Core Model of Earth's Structure, because they have little to do with that thread’s theme, speculation that the Earth’s core is not composed primarily or iron.

Didn't NASA show that the core is rotating faster than the surface, getting one rotation ahead about every 120 years?
Putting a New Spin on Earth's Core

If one considers the thick visco-plastic nature of the mantle, the huge moon sized core would need an extreme energy source to rotate faster. The iron core may add up in many ways if we ignore the faster core rotation, but it doesn't readily explain the extreme energy source, needed to move the moon sized core faster than the outer part of the earth, considering the viscosity drag. That drag should generate heat, which could explain some of the mantle heat. But it will also require a continuous energy source.

This needed engine could be why many are looking for alternatives explanations within the central most core. The inertia of the rotation of the earth is used to explain the magnetic field, so that of itself can not be the engine. This was all figured out and closed before we knew the core moved faster. That assumption would be further complicated by magnetic field reversals, which should then slow the core rotation, impacting the surface in some tangible way, which is not in the surface data or someone would have seen the historical anomalies. We need something else deep inside the iron core, that can be an engine that doesn't care about magnetic reversal but just chugs along for billions of years generating energy for rotation and mantle heat.

[CraigD]

Originally Posted by HydrogenBond

Didn't NASA show that the core is rotating faster than the surface, getting one rotation ahead about every 120 years?
Putting a New Spin on Earth's Core

If one considers the thick visco-plastic nature of the mantle, the huge moon sized core would need an extreme energy source to rotate faster. ...

The linked 1996 Harvard Gazette article strikes me as well-written and informative. However, I think HBond overlooked or misunderstood some critical points of Dziewonski and colleagues’ findings.

What is rotating slightly (according to the article, about 1°/year, or 0.0007%, though 2005 data and analysis estimate it at 0.3-0.5°/year) faster than most of the earth is not the entire core (radius about 3400 km, 55% of the Earth’s total), which borders on the mantle, but of the inner core only (1220 km, 20%). The boundry between the inner and outer core is defined by the transition from liquid to solid. According to the mainstream model (which is also Dzeirwonski’s), the inner core once didn’t exist, and has been and continued to grow as the Earth cools.

Nothing I read suggests the need for an “extreme energy source” for the different rates of rotation of the inner and outer core, and most suggest that it is caused by the liquid outer core inducing currents in and interacting magnetically with the solid inner core – behaving, in short, like an electric motor.

Give how small the difference in motion is, and that the inner core rotates faster, not slower, than the outer, I wonder, without having but serious effort into the question, whether it could be explained purely mechanically. As the inner core freezes out of the outer core, its formerly liquid matter forming crystalline bonds, it mechanically shortens its radius from the center of the earth. Perhaps, the inner core rotates slightly faster for the same reason that a figure skater can increasing her rotation by pulling her arms and legs inward.

Or perhaps it’s due to magnetic interaction of contact with convection currents in the outer core, and the inner core currently rotating slightly faster than the outer is a coincidence that. Were it measured millions of years earlier or later than now, perhaps it might be found to be rotating slightly slower.

PS: Though an interesting subject, this hasn’t much to do with speculation that the Earth’s core is not composed primarily iron, this thread’s theme, so if nobody objects, I’ll move posts about the different rate of rotation of the inner core to a new thread.

[modest]

Originally Posted by Pyrotex

I believe Craig explained the anomalous rotation correctly. The hot molten (mostly iron) core would have eventually rotated at the same rate as the surface of the Earth. Assuming that solid iron is more dense than its molten form, even under pressure, then as the core solidified, it would have contracted. This would have forced the core to spin a little faster, to conserve angular momentum. Given that the core is STILL going faster (though not by a lot), this would indicated that the friction between the solid and molten layers is not very large.

The earth also slows its rotation due to tidal friction of the moon. What used to be a 5-hour day is now a 24-hour day. I would wonder if the core could lag in that slowing.

~modest