Variations of this question have been asked and answered previously but I am looking for something specific.

Situation: Earth's body (mantel and crust) rotate at different rates than it's core (I think). The Earth's core is slowly freezing out & solidifying. The difference in the rate of rotation combined with convective motion creates Earth's magnetic field.


  1. How long will it take for the core to freeze out?
  2. What happens to humans when it does?
  3. Are there any sudden changes in the Earth's properties (rotation, magnetic field, etc) when it happens?

Note: I imagine the core freeze process will gradually synchronize the core and body of the Earth's rotation. I also imagine that we'll see a gradual weakening of the Earth's magnetic field.

Does anyone have numbers for these things?

  • 1
    $\begingroup$ Questions one and three might get better answers at earthscience.stackexchange. $\endgroup$
    – Samuel
    Jun 4, 2015 at 15:48
  • 2
    $\begingroup$ Actually there is a question there that asks a similar thing. The accepted answer is, in summary, the core will never freeze. At least not while Earth is in the solar system. $\endgroup$
    – Samuel
    Jun 4, 2015 at 15:57
  • $\begingroup$ Yet another question about a scenario that's already been made into a movie. Go watch The Core. $\endgroup$
    – ShemSeger
    Jun 4, 2015 at 19:17
  • $\begingroup$ Please don't make me do that, I beg of you! $\endgroup$
    – Jim2B
    Jun 4, 2015 at 19:18

1 Answer 1


I agree with @Samuel's suggestion that a few of these questions are better served else where. point up to you bud!

On that note your second question might have more to do with where Man is technologically when this hypothetical scenario occurs in the World you are building. Are we in pre-bronze age? current modern technology? or distant future where we have already traversed the stars and are spreading through the galaxy like a new plague? :) Will we survive or go extinct? So many factors here to consider.

As for the numbers, you can use these to get you started on your World Building project. The Earths current rotation is moving at 1675 km/h or 465 meters/second. The equator is 40,075 km and the length of time the Earth takes to complete one full turn on its axis is 23.93 hours for a sidereal day.

40,075 km/23.93 hours = 1,675 km/hour

As for the Cores rotation, yes you are correct they turn at different rates, and from what we currently know they actually move in Opposite Directions (this could be a great point for creating an inner world within your outer world for a game). It is understood from most studies that Earth's inner core is rotating faster than its surface by about 0.320 - 0.516 degrees per year.

As for changes (another great anomaly that could effect the world you build if they were over emphasized) researchers speculated that if the Earth's inner core is rotating faster than the rest of the planet, then shock waves from waveform doublets would enter and exit through different parts of the core despite originating from roughly the same spot on the planet's surface.

Another fascinating point recently being discussed in Scinetific communities is that the Daming of river systems around the globe is causing the earths roatation to slow down. You can read more here

So I hope those numbers help you in your World Building project.

  • $\begingroup$ Thanks. Small correction, they don't actually move in opposite directions. Another question on the earth science stack asked about that. $\endgroup$
    – Samuel
    Jun 4, 2015 at 16:32
  • $\begingroup$ the inner and outer cores do move in opposite directions, the outer core moves in the same direction as the crust though. read here $\endgroup$
    – Brian H
    Jun 4, 2015 at 16:59
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    $\begingroup$ The outer core appears to move in the opposite direction because it moves slower than the crust or inner core. Imagine a three lane freeway, you're in the left most lane and there is a car in the right most lane going nearly the same speed. You both pass a slower car in the middle lane, from your frame of reference it appears to be going in the opposite direction. From an external stationary observer, they're all going the same direction, just different speeds. If it was truly moving in the opposite direction it would be moving hundreds of miles per hour relative to the crust. $\endgroup$
    – Samuel
    Jun 4, 2015 at 17:45
  • $\begingroup$ If your frame of reference is the surface of the Earth then your statement is accurate. Just like if you were in that fast car and decided you were the stationary reference. But, you are making the claim while discussing sidereal time, from that frame of reference all the layers of the Earth are rotating in the same direction at very very slightly different rates. Your statement is wrong because of the context you placed it in. $\endgroup$
    – Samuel
    Jun 4, 2015 at 18:27

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