Extending straight lines too far beyond the present, however, is risky business, as noted by no less a scientific authority than Mark Twain. In "Life on the Mississippi" Twain noted that the Mississippi river was getting progressively shorter (mainly by floods--and by people--creating shortcuts through bends in the river) and he wrote: ...
"It is not impossible that the magnetic field will go through zero 1200 years from now, but (judging by the past record of reversals) not likely. In any case, the field is not going away: when one uses observations on the surface to reconstruct fields at the core, one finds that while the dipole field is getting weaker, the complicated parts are getting stronger, and the total magnetic energy does not change, within our observational accuracy. That's why I wrote "yes and no."
...I don't know about migrating animals (they may have magnetic organs, sort of built-in compasses), but there seem to exist no magnetic effects on DNA, resistance to antibiotics and so on; those changes seem more related to chemistry. ...
...David ..."
http://www-istp.gsfc.nasa.gov/stargaze/m…
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