#Planetary Magnetic Field
4 messages in this thread
Just curious speculation: the atmospheres of earth and other objects devoid
of a magnetic field differ. Earth's atmosphere below the ionised layers is a
relatively good insulator because it is not ionised. It may be arguable that
other objects are surrounded by either ionised inter-stellar gas or an ionised
atmosphere.
I must admit, I don't see exactly how this helps the hypothesis but it does
suggest that there may be more to the problem. Perhaps lightning plays a part
in equalising cosmic potentials in addition to the known local potentials
caused by thunderstorms.
Another aspect is the magnetic properties of the objects themselves. Rotating
electric effects only provide a magneto-motive-force, the resulting
field-strength depends on the magnetic properties of earth, Venus or whatever.
How about the known repeated reversals of earth's field. Any idea as to
current thinking about these and why magnetic north moves around true north ?
Peter.
Peter –
I moved this message to S12, figuring that the Geology types would have
the best answers to why the earth's magnetic field reverses or wanders around
true north. (BTW, it's the earth's magnetic SOUTH pole that wanders around
true north) I only know the suppositions on a crude scale: that the fields are
due to the convection currents in the earth's molten iron core, and that these
currents are coupled, but only weakly, to the axis of rotation.
I was just wondering this weekend, as I read a book on evolution and paleon-
tology, what effect field reversals would have on migratory animals that use
magnetic flux to guide them on their way.
I have yet to see any detail on the time period a reversal takes. Is it a
nearly instantaneous event or does it take kiloyears?
M
Hi, Michael–
Here are some messages from a while back with some bearing here. –Doug
#97371 S12/Geology
19-May-93 15:39:54 Sb: Magnetic Field Reversals Fm: James W. Keefer
71562,1543 To: ALL
Our earth science class is discussing ocean floor spreading and symmetrical
patterns of magnetic reversals on either side of the mid-ocean ridge. What
might be the ultimate or proximate cause(s) of magnetic reversals of the
earth's field, and how long would a reversal take to complete? jk
#97596 S12/Geology
23-May-93 00:55:04 Sb: #97371-Magnetic Field Reversals Fm: Richard Sedlock
71554,1103 To: James W. Keefer 71562,1543 (X)
Good questions! The greatest geophysical brains on the planet still haven't
come to a concensus, but here are some thoughts that might help you out.
If the Earth's magnetic field (EMF) is indeed caused by convection or some
other movement of the fluid, iron-rich outer core, then a reversal would seem
to require directional changes of that fluid. No one agrees on the size or
shape of the convection cells.
Reversals can probably occur within a few thousand years, based on careful
paleomagnetic rocks of well-dated rocks on land.
Problema grande: the huge energy needed to halt the momentum of convecting
molten iron in the outer core in a few thousand years, not to mention starting
it up again in the other direction.
Whoever figures this all out is going to sweep the available physics and
geophysics awards. Good luck. rs
#97835 S12/Geology
26-May-93 21:40:23 Sb: #97596-Magnetic Field Reversals Fm: Stephen Ryland
72345,366 To: Richard Sedlock 71554,1103 (X)
Yes, I think there was a nice summary article in the last few issues of EOS.
I think they were making the point that it was longer rather than shorter; a
long time ago we used to think it was very fast and could have
semi-catastrophic consequences.
Steve
#99047 S12/Geology
13-Jun-93 23:52:32 Sb: Magnetic Field Reversals Fm: Bill Duxbury 72172,656
This is an area of true possibilities in research. Like so much of the evidence
regarding Continental drift, this one opens up as many questions as it answers.
The source and amount of energy required to change the direction of a magmatic
mass is a mystery.
As a pilot, I'm glad to here that the reversal is relatively slow. I would
hate to be flying a load of people from Washington D.C. to L.A. when the
magnetic poles switched! Our on board navigation systems whould not be happy.
Dux
#99235 S12/Geology
15-Jun-93 22:39:16 Sb: #99047-Magnetic Field Reversals Fm: Emory Kimbrough
(Sysop) 72777,1553 To: Bill Duxbury 72172,656
The current issue of _Science News_ (June 12) has a nice three-page review of
the current status of the shouting mat….er….debate on this topic.