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