I’m told – a book I’m reading – that the Earth’s magnetic poles reverse, or is it the field that reverses, at times. OK, so, all of us even vaguely scientifically literate know that. The “vaguely” is the important thing here.
So, I’m told that it reverses, well, not randomly, but at unknown in advance dates. And when it does, it does so pretty quickly. But that’s quickly in geologic time. So, bumble along for a few hundred thousand, mebbe tens of millions, of years. Then the magnetic field weakens, wibbles, then over perhaps 4,000 years reverses and strengthens again.
It’s the 4 k years interregnum that interests. That the North Pole becomes the South Pole doesn’t bother me.
But the Van Allen belts, they protect us all from solar radiation. And some say that without that protection we’d all fry. I assume, but don’t know, that the Van Allen stuff is the product of the same magnetic fields that produce north and south poles. So, the reversal means 4k years of light to no Van Allen belts.
1) Why haven’t all land mammals repeatedly fried every polarity reverse?
2) They have and this is punctuated equilibrium?
3) Sure, we’ve got enough electromagnetic stuff out there that full exposure to the solar wind will fry civilisation – there’s a reason why space hardened computer chips really are different.
So, using this as a fictional device you can definitely kill civilisation and reduce population through polarity reverse. Could you though get away with it forcing the punctuation of the equilibrium and, say, get to Eloi and Morlocks as a story device?
This depends upon two assumptions. That absence of the Van Allen belts causes real problems and also that the reversal, or the weakness coincident with it, kills the Van Allen belts for that period of time.