[DB 1506 (1); OAB 50] Since devices for measuring the Earth's magnetic field were invented a few hundred years ago, measurements have shown that the Earth's magnetic field has been steadily decreasing over those few hundred years. It is claimed that these measurements indicate that the Earth's magnetic field has been steadily losing energy ever since it formed. By extrapolating the decay backwards in time, it is then claimed that an age greater than 10,000 years is impossible. However, it is easily shown that such a simple extrapolation is not justified. Scientific instruments are not the only mechanisms that have ever existed for measuring the Earth's magnetic field. Ovens used by ancient civilizations and the igneous rocks making up the ocean floor are two of the more obvious examples. Both record the direction and strength of the magnetic field as it was at the time they were last heated, and both prove conclusively that the hypothetical exponential decay of Earth's magnetic field has not occurred (according to the young-Earth theories, the magnetic field was many times greater only a few thousand years ago, a hypothesis that is clearly at odds with the above-mentioned evidence). Instead, the evidence shows that the magnetic field has fluctuated back and forth in strength as well as direction. These fluctuations are clearly observed in places where the stratigraphy (i.e. which rocks are older than which rocks) is obvious due to either layering or distance from a sea-floor spreading ridge. The decrease measured in the past few hundred years, therefore, is nothing more than a downward trend as part of an overall fluctuation, and has no implication for the age of the Earth (for a more detailed discussion of this issue, see Thompson (1997), http://www.talkorigins.org/faqs/magfields.html).

 

It has been proposed by Young-Earth scientists that all of the magnetic reversals recorded in the sea floor were created during Noah's Flood. There are several problems with this theory that make it physically implausible, but regardless of whether or not this theory is valid, the fact remains that a coherent Old-Earth theory exists to explain the recent decline in Earth's magnetic field strength. Therefore, that decline should not be used to argue against an ancient Earth.