magnetic field and series polarity?

Question

The magnetic field of Earth has had (3,5,7) intervals of reversed polarity during the past 4 million years.

Choose your answer from the three options in the parenthesis.

Answer 1

i once saw it on discovery channel and i presume it is 20.

Answer 2

I don't see that there has ever been a reversal. If we did we would loose our ozone layer of protection and it might be for some time which would completely sterilize the earth. They find magnetic material that is not aligned with the poles and go on from there. I think it is very unlikely, need much better info.