I really wish I knew what "reversals" in Earth's magnetic field means. Personally I 'believe' there was a time when due north and magnetic north were in unison and there will come a time when the two are set back in alignment.
Now the notion 'origins' is not 'out' of Africa is almost enough to shake this old earth back into its original orbit.
Reversals in the Earth’s magnetic field means, the magnetic poles of the Earth have shifted in short amounts of time, and many more times than once or twice; and the shifts (which are recorded in ferrous rocks that used to be molten lava) are not related to continental drift.
Large changes of the earth's magnetic fields in historical timesBy measuring the magnetic properties of bricks and other accurately dated human artifacts, geophysicists can reconstruct the history of the local magnetic field. Near Loyang, China, the field was as much as 54% higher in 300 A.D. than it is now. It was 15% higher in 1500 A.D. In 1000, it was less than today's value.
by William R. Corliss
Science Frontiers #22: Jul-Aug 1982
(Wei, Q.Y., et al; "Intensity of the Geomagnetic Field near Loyang, China, between 500 BC and AD 1900," Nature, 296:728, 1982.)
Comment. Direct measurements of the earth's field go back only a few hundred years, but they are consistent with the data reconstructed from artifacts, both showing a steady decrease since 1500. No one has estimated the effects of these substantial changes on radiocarbon dating and, perhaps, human biology.
[old note of mine I saved from another topic] Since the magnetic pole shifts in the fossil record don’t seem to be uniformly spaced, at all, the cause of them is probably external. Since I was a Boy Scout (hard to believe, I know) the magnetic north pole has moved hundreds of miles.
Re: magnetic reversals. This site gives a pretty concise explanation of it.
http://www.geomag.bgs.ac.uk/education/reversals.html