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It’s freezing; no wait, it’s melting… May 23, 2011

Posted by mareserinitatis in engineerblogs.org, geophysics, papers, research, science.
Tags: , , ,

First order of business is to send you to EngineerBlogs.org where I posted today on how engineers who do simulation are not, in fact, inept experimentalists.  Just come back after you’ve read it (and commented!).

Are you done yet?

The other thing I wanted to mention was that I came across an article on LabSpaces about how Earth’s core may be continually freezing and melting.  I am interested because of implications for the geodynamo.  (As a side note, I haven’t read the paper directly, just commenting on the LabSpaces post.)

Earth’s outer core is composed primarily of molten iron, but there are some lighter elements in there.  The generally accepted theory is that most of the energy to power the geodynamo (which generates Earth’s magnetic field) comes from the freezing of the outer core.  It’s still really hot down there, but the pressure is so high that the iron can become solid.  As the iron freezes out, it releases energy.  Another source of energy is the rising of the lighter elements as they don’t freeze out.

There are some problems with this theory.  First is that the iron isn’t freezing out at a rate to produce sufficient amounts of energy to power the geodynamo.  That is, it provides some of the energy, but not all of it.  If this freezing out process were to produce the amount of energy needed to power the geodynamo entirely, it would have entirely solidified in about a billion years.  The planet has been here for about 4 billion, so obviously that’s not what’s going.  Second, the amount of energy generated by the inner core is proportional to its surface area.  This means that you would expect Earth’s magnetic field to increase over time as the inner core grew.  Experimental evidence suggests that Earth’s magnetic field strength was about the same, even 3 billion years ago.

The theory that the inner core is continually freezing and melting again might change some of the perspective on this.  If the core freezes and generates energy and then melts again, this could potentially explain why the core hasn’t frozen out and may lead one to believe the core may have been growing for longer than anticipated.  On the other hand, if the remelting process consumes a significant amount of energy, it could definitely not help with the energy balance issues.  If this process is consuming a lot of energy, then that may actually exacerbate the problem because that means more energy may need to come from some other mechanism.



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