Elsewhere, I started a thread about the Earth's magnetic poles switching. My information was greeted with quite a bit of indifference <sniff>.
Regarding one hypothesis of the condition in which we find Mars is that it too had a protective magnet field that, most importantly, prevented the solar winds from wearing away most of the Mars' atmosphere. Consider also that Mars' specific gravity is less than ours so it had less attractant qualities to hold onto its atmosphere.