If Magnetic Field protects us from cosmic ray, Why didn't Magnetic Field Reversal kill all the animals/plants?

Question

If Magnetic Field protects us from cosmic ray, Why didn't Magnetic Field Reversal kill all the animals/plants? There are several Magnetic field reversals which reduced Magnetic field to almost zero.

Answer 1

The magnetic field doesn't protect against all cosmic rays. Technically cosmic rays are extra-solar in origin, and are little effected by the magnetic field. Its definition has been expanded to include the stream of ionised particles called the "solar wind".

What the magnetic field does do is shield the earth from that solar wind flowing from the sun. Without the magnetic field, the earth would be bombarded by a steady stream of ionised particles from the sun. But most of those particles would still be stopped by the atmosphere. There would be a noticeable increase in ionised energy at the surface, but not enough to kill off all life. Just enough to increase the rate of mutation.

The greater danger of losing our magnetic field is that the solar wind would strip the earth of its atmosphere. The magnetic field rises above the atmosphere and deflects the solar wind around the earth, protecting our atmosphere. Mars, which has no magnetic field has had its atmosphere almost completely eroded away.

BUT... this takes a great deal of time, and geologically speaking, the flipping of the magnet field is an extremely quick event (on the order of a few hundred to a few thousand years). There simply isn't enough time for the solar wind to do any significant damage in that short a timespan.

So... no mass die off from increased radiation because the increase would be too small, even over a long period, and no loss of atmosphere because the flip happens too quickly.

BTW... the magnetic field *IS* failing, fast. It's quite a bit overdue for a flip, so we may actually be entering that period soon (say the next 100 - 200 years, so don't hold your breath).

Answer 2

Ian was doing so well till he said "BUT". Polar reversals take tens of thousands of years to complete. In the interim, secondary dipoles, not located near the axial poles, assume the function of the primary dipoles. As a primary dipole is diminishing a secondary dipole is emerging. The fact is that most solar radiation is carried to the magnetic poles (the Aurora Borealis and the Aurora Australis), which at this time are covered with snow and ice. This is not the normal case in the Earth's history. The Earth has rare periods of glaciation, and we are in one of those rare periods. Typical Earth conditions do not show evidence of ice, even at the poles. I am sure that there is damage done to the biosphere during polar reversals, just as there is damage done to the biosphere during normal conditions. The area affected is a small percentage of the Earth, and biota not living at the magnetic poles is not damaged, which is the vast majority of the Earth. There is no time when the magnetic field is "zero", for that would require a completely different Earth with no nickel-iron core.

Answer 3

Reversal of the magnetic field does not imply that it diminishes or reduces or disappears completely! And maybe I missed something, but I never heard of any record of the field diminishing to almost zero! There are records in the rocks of reversals, by diminishing to almost zero! I don't think so.

Answer 4

You're right but wrong. It depends on what type of MFR you are talking about. I know a little about this subject, not enough to answer it to your best but there are field reversals every "set period" of years. I'm just not sure what the time period is. But they occur often and in your lifetime.

If you know of several MFR's which reduced MF to almost zero why don't you know anything else about it??? Maybe you should do more or at least your own research.