MadSci Network: Evolution

Re: What effects did the Paleomagnetic reversals of the poles have on life, if any?

Date: Thu Sep 2 12:23:18 1999
Posted By: Mike Klymkowsky, Professor
Area of science: Evolution
ID: 935275959.Ev

reversal While creationists  argue that the observed decay in the earth magnetic field is evidence for a young earth, it is clear that the earth has had a magnetic field for at least 3,000,000,000 years.  The periodic reversals of the magnetic poles is an interesting phenomena that illustrates both the structure and dynamic nature of the earth (see Los Alamos - Geodynamics site).  While magnetic field reversals has been used to date rock (see Dating page), there has not been a lot of work on the biological effects of pole reversal.  We can speculate however.

    The earth's magnetic field is important in shielding the earth from cosmic rays, by focussing them towards the poles (where they appear as the Northern and Southern lights).  During a field reversal, we would expect this shielding effect to  weaken.  This could increase mutation rates, leading to increased variation within populations.  Since natural selection works on variation within populations, some increase in evolutionary rate might be observed.  On the other hand, it is conceivable that organisms, highly specialized to a particular environment, could be driven to extinction.

    A number of organisms depend upon sensing the earth's magnetic field more directly.  There are magnetotatic bacteria that use internal magnets to direct their movement along magnetic field lines.  Similarly, homing pigeons (and sharks and honey bees) have internal 'brain magnets" that are used to navigate.  During magnetic field reversal, they could become disoriented.  It is important to remember, however, that the earth's magnetic field is generated by convection currents within its molten outer core, and  changes in these currents do not happen overnight.  It takes about ~1000 years, for the field to reverse, a long time compared to the life time of a particular individual.  It is likely that organisms would  adapt to the changing magnetic field by using other environmental clues, and so minimize the effects of pole reversal on their behavior.

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