We are protected from the constant stream of charged particles coming from our sun by the magnetic field, which deflects them around the earth and directs some of the wind to the poles.  Our sun has a strong magnetic field generated by a strong dynamo of moving charges within it’s powerful convection cells.

Similarly, the liquid portion of Earth’s mantle churns and generates the field that protects our oceans, atmosphere, and life from the solar wind.  In the last post I discussed the atmosphere and water that Mars may have had in it’s past, and how the progressive freezing of it’s core contributed to the weakening of it’s magnetic field, and the subsequent stripping of it’s atmosphere.

The sun reverses polarity on an 11 year cycle.  Earth does the same, but with less regularity.  As you can see from the plot, we are overdue for one. As we look back at the basaltic rock record expanding from the mid ocean ridges, we can see from samples of magnetite that Earth’s polarity has reversed many times in our geologic history.  What would happen on earth during one of these reversals, when the field is weak and chaotic?  In class, freshman year, I naively asked if there would be aurora everywhere.  While this would be amazing, it is unlikely.  Rather, the scattered and multiplied poles would channel less of the total solar wind, and while they may exhibit their own aurora, it would be less intense than that which we observe now.  During the last brief reversal, the field is estimated to have had 5% of it’s current strength. It would be likely that one of these periods ranging from 200 to 10,000 years would be hard on life, but reversals do not correlate with extinctions in the fossil record, so it is likely that we would live through it.

This photo is from a computer simulation of earth’s convective liquid mantle. The polarity reversed at irregular intervals, and the behavior of earth’s field was actually well matched.

Vacquier, Victor (1972). Geomagnetism in marine geology (2nd ed.). Amsterdam: Elsevier Science. p. 38. ISBN 9780080870427.

Glatzmaier, Gary. “The Geodynamo”.

“Earth’s Inconstant Magnetic Field”. Retrieved 01-07-11.

Merrill, Ronald T.; McElhinny, Michael W.; McFadden, Phillip L. (1998). The magnetic field of the earth: paleomagnetism, the core, and the deep mantle. Academic Press. ISBN 978-0-12-491246-5.