Why is the earth's magnetic core steady?
lardom
Posts: 1,659
I was reading an article when I asked myself, "If the earth's core is molten and the plates shift how do the magnetic poles remain so steady?" Since I'm on the subject of the earth's core I have also wondered if low level fission is what keeps the core hot.
Comments
Most of earth's magnetic field is generated by processes at the earth's core. The earth's crust (where tectonics takes place) is literally just a thin scum of material that only slightly affects the field emanating from the core. So changes in earth's magnetic field are mostly caused by massive changes deep inside the earth.
But having said that, I should also add that the earth's magnetic field is perhaps not as steady as you suggest. It can change minute by minute as it interacts with magnetic fields in the solar wind. For other reasons, the poles themselves can drift around over periods of mere years, causing the magnetic declination to change (earth's magnetic north does not match earth's true north). Even more dramatically, the earth's magnetic field sometimes completely flips, so that today's magnetic north will become south, and vice versa. These large changes are a result of how the iron-nickel core of the earth forms some kind of hydrodynamic dynamo effect, which I think is still poorly understood.
http://en.wikipedia.org/wiki/Magnetotelluric
http://en.wikipedia.org/wiki/Magnetic_declination
http://en.wikipedia.org/wiki/Geomagnetic_reversal
As for radiogenic heating inside the earth. First, understand that all those miles of rock act as a fairly good insulator. Then consider that there are many isotopes in earth's crust and in earth's mantle that are somewhat radioactive, so over time they radioactively decay, which is a process that releases energy, and since that energy has no way of radiating out of the planet because of all the rock surrounding it, it ends up as heat.
The ability of radioactive decay to generate heat has been used for decades to generate electricity in radioisotope thermoelectric generators.
http://en.wikipedia.org/wiki/Radioisotope_thermoelectric_generator
It is possible the earth's core is NOT molten. Those who determine these things have a long history of being wrong about many things. (Like the earth is flat for example...)
And so far as volcanoes go, it could be just the massive forces of the oceans pressing sideways on land masses which causes that? And the "molten" is only near the surface?
Anyway keep an open mind about these things.
They can tell what the layers of the earth are like from the way eathquake waves move. Shear waves don't pass through liquid.
I think it's thanks to the people who determine these things that we don't still think the world is flat.
I think science has a better track record for finding out the way the world works than reading tea leaves.
I hope, not so open as to let one's brain fall out.
I'm kind of closed minded about Zeus not being the cause thunder by throwing his lightning bolts.
Edit:
@Bill, I just tried to delete this message (but the forum software wouldn't let me). When I read it, it sounded too harse. This isn't supposed to be an argument against you, I just wanted to state my "Pro-Science" stance. I think science has done a pretty good job and it beats the alternatives for finding out how many things in the world work.
Anything is possible. But most of what geophysicists think about the inner earth comes from their study of how seismic waves, generated by earthquakes, travel through the earth. P waves, for example, can travel through fluids as well as solids. But S waves (which impart a shearing force on materials) can not be supported by a fluid - they can propagate only through solids. S waves never make it through the earth's core area, so one explanation of why S waves can't make it through the core is that the core is not a solid.
Of course, humans have very little data dealing with materials at such high pressures and temperatures, so what the earth's core really "is" is difficult to tell.
Man, how wrong can you get? It's Thor who does that! And he uses a hammer!
Okay, I'm still open minded about Thor.
Oh that is quite allright!
I expected a bit of discussion and prefer people express their opinions. Actually I think the first people to suggest the earth was round had shortened life spans...
I wonder if that means Australia will no longer be "The Land Down Under"?
Amanda
Yes I've wondered that too. In the crust, all the elements are locked in place, but under the crust everything is a liquid, and in a liquid the denser elements are going to fall to the center. The densest element is uranium - far denser than iron. So if all the uranium ends up in the center would there be enough to start some sort of reaction?
Searches along these lines takes one to the 'fringe' parts of science on the internet. But I believe that it was years and years ago (?1800s) someone did the maths of how long a body like the earth would take to cool down over billions of years and it shouldn't be as hot internally as it is.
I don't know if the heat comes from fission or just radioactive decay. Interesting read here http://www.spacedaily.com/news/earth-03k.html
I think there is evidence that natural fission reactors can occur http://en.wikipedia.org/wiki/Natural_nuclear_fission_reactor
The sun also imparts a tidal force. So I guess we'd have to lock in the sun, the moon, and whatever else is out there jerking us around.
Then again 7th grade was something like 30 years ago, so that could have something to do with it.
I found another article from Oak Ridge National Laboratory which I think is part of the US Dept of Energy so it may have a bit more gravitas http://www.pnas.org/content/98/20/11085.full
From a questioning, skeptic point of view, if neutrinos can be detected from reactors on the surface, and even sent through the earth as has been done, is it possible to detect neutrinos from the center of the earth?
One thing this model does explain though is how the earth's magnetic field can switch off at times. I don't think that can be explained so well by just isotope decay or tidal heating.
Interesting to compare the output of this sort of hypothetical reactor (4-5 terawatts) with global energy consumption (15 terawatts).
Well, heck, I guess I forgot that. Seems like that's been the accepted version for many decades. Duh on me. http://en.wikipedia.org/wiki/Inner_core
Certainly there is an inner core of higher density, and a measurable density boundary, but they claim this is at 5505 °C, so you then have to factor in the very high pressures, to decide where this sits between 'more solid', than 'more liquid'.
If you've seen how steel can buckle and plastic-flow, when well inside what we call 'solid' (ie barely glowing) you can see it is a poor word to use.
True. I guess just because a layer reflects sound doesn't mean it is necessarily a solid, does it? IIRC, thermoclines can reflect acoustic energy. So could the "solid" core really be just some sort of density discontinuity? In any case, at those depths and at those temperatures, what difference does it really make what we think it is? I know if I were down there, I probably wouldn't argue with anyone over solid core vs. liquid core. Instead, I'd be asking Kenneth Lay what he did with my money.
http://oil-price.net/en/articles/oil-drilling-expensive-business.php
I think it's a case of Satan getting to it before we do.
It is an interesting thought, as Dr_Acula has suggested, that uranium's density might cause it to sink to the center. A quote from Dr_A's link; Maybe the earth's magnetism and a nuclear reaction are related assuming that a reaction takes place.
One good thing is that even if the poles flip from time to time magnetism still deflects the solar wind.
(I didn't want to post anything because these are recurring questions in my head and it will annoy me if I put the brakes on the discussion.)
What about during the flip itself? I'm guessing it takes a few weeks or months or years??? If so, how vulnerable is life when our shields are down?
I hope it doesn't occur during my lifetime. (BTW, keep a safe distance from Ken Lay...)
Don't think uranium can sink, its a very reactive metal and exists only as much lighter compounds like oxides and silicates. Iron is less reactive and substantial quantities exist in metallic form so sinks. I suspect the vast majority of gold/platinum metals in the planet exists in solution in the core as they are unreactive and dense.