Not just possible. Likely. The Brunhes–Matuyama reversal was 780k years ago and the average gap is only 450k years http://en.wikipedia.org/wiki/Geomagnetic_reve

Not just possible. Likely. The Brunhes–Matuyama reversal was 780k years ago and the average gap is only 450k years http://en.wikipedia.org/wiki/Geomagnetic_reversal http://en.wikipedia.org/wiki/Geomagnetic_reversal. Such reversal events can cause thousands of years of fluctuating protection from solar radiation. I'd be fascinated to see a study of how we might protect ourselves during such an event. Sadly I imagine nobody wants to be the guy that spent billions on EM shielding 50,000 years before anyone needed it.