USGS Frequently Asked Questions

Answer:

The magnetic field of the Earth does protect us from fast-moving charged particles streaming from the Sun, but so does the atmosphere. It is not clear whether or not the radiation that would make it to the Earth’s surface during a polarity transition, when the magnetic field is relatively weak, is sufficient to affect evolution, either directly or indirectly, and cause extinctions, such as that of the dinosaurs. But it seems that the radiation is probably insufficient. This conclusion is supported by the fact that reversals happen rather frequently, every million years or so, compared to the occurrence of mass extinctions, every hundred million years or so. In other words, many reversals and, in fact, most reversals, appear to be of no consequence for extinctions.