Re: Lowest frequency
I am pretty sure the switch will happen. There is a big rift in the middle of the pacific ocean, and they can run a magnetometer over the area and see a complete change in the magnetic orientation of the cooled magma in distinct bands (time) over the millenia. Also, on only good navigation map, you will notice that the magnetic declination is always changing with time, albeit slowly. They tell you the magnetic declination on the date the map was published, so you can recalibrate it in future years.
I just wonder if it takes time to swap poles, and if the magnetic fields at the poles are the only thing keeping us from being fried by nasty high energy space particles, what happens for the year(s) when it is actually swapping poles midway? Do we still get the magnetic field protection, or does our magnetic shield die out for a while when the switch happens?