CompuServe Thread

Gary, >> So, if we believe that these reversal happen quickly, i.e., you wake up the next day and your compass needle points south instead of north, this would confuse the whole concept of App. polar wandering. << You might think that, but no it doesn't, largely because the reversal is just about exactly along the magnetic axis. Look at it this way: Say you're scanning a mineral crystal that's one of these magnetic-sensitive types, and you find the crystals looking like this as you go along (arrows point toward magnetic north): ————> ———–> ————–> ———–> ———> ———–> ———–> ———–> ————> As you move along, you notice that the alignment gets a bit sloppier (or whatever), indicating a fading magnetic field. Then you find a band of rock where there's no magnetic alignment at all. On the other side of that, the alignment reforms and gets firmer again, indicating a strengthening field. Only this time the arrows look like this: <———— <———– <———– <———– <——— <———– <———– <———– <———- Now, you know from looking at these minerals that magnetic north switched from *this* way ——-> to *that* way <——–. That's polar reversal. But the axis of the field hasn't changed. There was a pole in *this* direction ——-> and there still is, it's just that it's switched polarities, from north pole to south pole. The mineral always aligns along the magnetic field lines. The _line_ is all you need to find the location of the pole that's in this direction ——>. You don't need to know the polarity. Jon W. .