Could anybody tell me why the poles of this planet shift? I heard we’re due for one soon, (within the next several thousand years so someone has told me). But I have no idea of the mechanics behind this, can anyone enlighten me before I have to turn all of my wall maps upside down.
The rotational axis of the Earth does not shift, although it is known to wobble a little. The magnetic field of the Earth does change its intensity and alignment in a very regular manner (on a large scale) and also shifts in relation to the rotational poles. I don’t know the “why” but it may have something to do with the currents of molten iron in the core that produces the magnetism.
Read Ken Kesey’s novel Sailor Song for a fictional description of a pole shift in the near future. (Whoops, hope that isn’t a spoiler – it occurs late in the novel.)
People in Alaska saw things like giant purple bacon, curly at the edges and making sizzling crackling sounds, flying south away from the North Pole. After that, all electrical devices did not work; there was no more electric power at all. The newspaper had to be produced with manual typewriter and carbon paper, the masthead printed with carved potatoes.
Some planets have undergone true rotational axis shifts. Venus rotates “backwards” and Uranus is lying on its side. As was stated above, nothing like this has occurred on this planet. Considering the huge momentum shift involved, it’s a good thing it hasn’t. We’d have more trouble than just having to print newspapers with potatoes.
When the planet’s magnetic field reverses, how quickly does this happen? I know it happens rapidly in geological terms, but so does everything else that’s not geology. I have a vague impression that I can’t account for that it happens slowly – for several tens of thousands of years the magnetic field grows weaker, goes to zero and slowly builds up again with the opposite polarity. Is tens of thousands of years about right? If not, what’s the time scale?
Bueller? Bueller? Anyone? Anyone?
The magnetic field of the Earth is due to a dynamo effect, like that of the Sun, which means that it’s formed by the rotation of a conductive fluid. However, the Sun’s dynamo fluid is a nice, predictable plasma, while the Earth’s is a messy, viscous liquid, so it’s a lot harder to say anything about it. If the Earth’s pole-flipping behaves similarly to the Sun’s, though, it wouldn’t be instantaneous. In the Sun, magnetic field lines end up getting so tangled up that they start cancelling and disappearing, eventually leading to no net magnetic field, at which time it starts building up again. Note that this might still be destructive, it’d just be slower destruction.
To expand on Chronos’ explanation, the fluid in question is liquid iron, which is what the outer core consists of (the inner core is solid iron). The magnetic field is created by the circulation of this liquid iron within the core.
The polarity of the magnetic field reverses at irregular intervals, and the reversal takes, IIRC, between hundreds and thousands of years. So during this process I suppose birds are really confused about which direction to fly.
Actually, a lot of cosmological processes take a lot of time in geological terms :).
The term “pole” is slightly misleading when applied to the magnetic field, since it makes people think that the magnetic poles are analogous to the rotational poles. In fact, the magnetic poles are simply the points with highest magnetic potential from each other. They are not necessarily on opposite sides of the Earth from each other, and the magnetic field is not symmetric around them. And while magnets (aka compasses) will point in their general direction, a large local anamoly in the magnetic field can cause a magnet to point in a slightly different direction.