The field strength should decrease by a constant percentage each year, and the data are consistent with such a decrease, implying that the field loses half its strength every 1400 years.
Such a rapid decay could not have continued for more than about 10,000 years; otherwise the initial strength of the field would have been impossibly high.
However, such "dynamo" theories are complex, implausible, and incomplete.
In the last two decades, they have run into serious problems from magnetic observations on earth His simple and rigorous "free-decay" theory would mean that the current is running down slowly, like a flywheel without a motor; thus the strength of the earth's magnetic field would be steadily decreasing over the centuries.
There were so many spinning nuclei in the earth at creation that, if aligned, their fields would have added up to a large field of sufficient magnitude.
As thermal collisions disoriented the nuclear spins, the laws of electricity predict a startup of an electric current within the core of the earth to sustain the field.
Many atomic nuclei spin, and thereby generate tiny magnetic fields.In 1984, 1 extended my theory to the sun, moon, and planets, explaining the magnetic fields measured by the space probes of the last few decades, and predicting the approximate strength of the fields of Uranus and Neptune. In 1986, Voyager 2 verified the Uranus prediction, and we should find out about Neptune in early 1990. After creation (and the Fall), the electric current in the earth's core would decay slowly, as would the field, for 1656 years, until the Genesis flood. Since the field probably started when the earth was formed, the present rapid decay of the field is strong evidence for a young earth.Old-earth proponents, however, correctly point out that the earth's magnetic field has not always decayed smoothly.