Geologic dating decay constant table
According to the dynamic-decay theory, the true age would be less than that because of extra losses during the reversals and fluctuations.
The solid line (labeled "dynamic decay") shows that with a significant loss of energy during the Genesis flood, the age of the field would be about 6000 years. The precise age limits above depend not only on the dynamic decay theory, but also on the theory of planetary magnetic-field origins.
Thomas Barnes, a creationist physicist, began publicizing it in 1971. He pointed out that such a decay would occur very naturally if the electrical current producing the field were slowly losing energy because of the electrical resistance of the core. This theory is called "free decay." The observed decay rate is exactly what one would expect from the electrical properties of the materials most likely to be in the core. The free-decay theory contradicts the evolutionary "dynamo" theories, which claim that complex processes in the earth's core have converted heat energy into electrical energy, much like an electric generator, maintaining the field for billions of years. Many intelligent scientists have been working on dynamo theories for over four decades without great success.
Furthermore, recent measurements of electric currents in the sea floor weigh heavily against the most popular class of dynamo theories. Thus evolutionary dynamo theories do not have a good explanation for the rapid decay of the field, whereas the free-decay theory does.
But even in this extreme case, the maximum age would still be only about 100,000 years, far short of the billions of years evolution needs.
Conclusion At present, the only working theory for the origin, fluctuations, rapid reversals, and decay of the field is a creationist theory--a theory that fits all the data.
However, our historical data on the intensity of the field only goes back to 1829. Fortunately, there is a scientific way to answer that question.
"Archaeomagnetism" is the study of the magnetization of bricks, pottery, campfire stones, and other man-related objects studied by archaeologists.
Archaeomagnetic data taken worldwide show that the intensity of the earth's magnetic field was about 40% greater in 1000 A. than it is today, and that it has declined steadily since then. Such a rapid decay could not have been going on continuously for millions of years, because the field would have to have been impossibly strong in the past in order for it to still exist today.A final fluctuation slowly increased the intensity until it reached a peak (50% higher than today) at about the time of Christ. "Paleomagnetism" is the study of magnetization locked into rocks at the time of their formation.Paleomagnetic data show that while the geologic strata were being laid down, the earth's magnetic field reversed its direction hundreds of times.It is also possible that a small percentage of today's energy decay is not free decay, due to the core's electrical resistance; but rather is dynamic decay, due to residual motions in the core fluid.In that case, the resistance of the core would be less, and the maximum age of the field would be greater.