[aimhigh]

this flow of energy should keep the Earth's magnetic field going for another billion years or more.

Ya, except for those brief periods when the magnetic poles flip.

[MUDDOG]

Here's an interesting article on the effects of a pole flip:

What if Earth's Magnetic Poles Flip?

It says the atmosphere would still provide protection from most of the sun's radiation, at the earth's surface, but our satellites could get knocked out.

It also cites a theory that the Neanderthals were wiped out by a magnetic field weakening (that didn't get all the way to a flip).