Re: Any correlation between mass extinctions and reversal of magnetic field?

First, let me give some background information. The earth's magnetic field has changed polarity many times and indications are that it might be getting ready to do so again in the near future (geologically speaking). When this happens, our exposure to cosmic radition will increase a little because the magnetic field provides some protection against charged particles (such as protons or electrons) from the sun and elsewhere in the galaxy. In addition, some of these charged particles can create radioactive atoms such as tritium and C-14. So our radiation dose from these natural radionuclides will increase, too.

The good news is that the increase in radiation dose will probably not be very large compared to the natural background radiation exposure from all sources. The two largest sources of background radiation are radon and naturally-radioactive potassium in our own bodies. The third largest source is natural radioactivity in rocks and soils. So, even though radiation dose from cosmic radiation will increase, it won't be enough to wipe out life on earth, or even to make it unpleasant.

So, to answer your question, there seems to be no correlation between magnetic field reversals and mass extinctions and no reason to suspect one.

You can find further reading on natural sources of radiation exposure in a wonderful report by the National Council on Radiation Protection and Measurements, it's called "NCRP Report #94: Exposure of the Population in the United States and Canada from Natural Background Radiation".