Earth's magnetic field is decaying, indicating a young earth (Talk.Origins)
- Earth's magnetic field is decaying at a rate indicating that the earth must be young.
Source: Barnes, Thomas G., 1973. Origin and destiny of Earth's magnetic field, ICR Technical Monograph No. 4. El Cajon, CA: ICR. Humphreys, D. Russell, 1986. Reversals of the Earth's magnetic field during the Genesis Flood. Proceedings of the 1st International Conference on Creationism, Creation Science Fellowship, 2: 113-126. Humphreys, Russell, 1993. The Earth's magnetic field is young. Impact 242 (Aug. 1993).
CreationWiki response: (Talk.Origins quotes in blue)
1. Empirical measurement of earth's magnetic field doesn't show exponential decay. Yes, an exponential curve can be fit to historical measurements, but an exponential curve can be fit to any set of points. A straight line fits better.
Not true. First of all the general trend in the empirical data of earth's magnetic field shows the shallowing out that is expected with an exponential curve. Second an exponential curve is more in line with the physics of a changing magnetic field than a straight line.
Dr. Jonathan Sarfati wrote:
- ...it is a well-accepted procedure in modeling of regression analysis to use meaningful equations to describe physical phenomena, where there is a sound theoretical basis for doing so. This is the case here. Currents in resistance/inductance circuits always decay exponentially, not linearly, after the power is switched off.
- A liner decay might look good on paper, but it's physically absurd when dealing with the real world of electric circuits. In fact, linear decays of anything are rare in nature. Conversely, exponential decay is firmly rooted in electromagnetic theory.
- Another important point is that even if we accept the skeptic's argument about a linear decay, it would still point to an upper limit of 90 million years, and this is far too young for evolution...
- (Sarfati, 2004, pp. 338-339, emphases in original)
- Earth's Magnetic Age
- The Earth’s Magnetic Field is Still Losing Energy
- Refuting Compromise, Dr. Jonathan Sarfati, 2004, Master Books
2. The earth's magnetic field is known to have varied in intensity [Gee et al. 2000] and reversed in polarity numerous times in Earth's history. This is entirely consistent with conventional models [Glatzmaier and Roberts 1995]
While there is evidence of past variation in intensity and even reversals, the actual data does not support conventional models. The pattern used to show reversals consistent with the conventional models is only a small portion of the actual data, much of the rest show major contradictions with the conventional models.
In addition magnetic reversals in rock may be a result of magnet ostriction which changes the direction of magnetized igneous rocks due to distortions in the rock resulting from shock or stress.
- and geophysical evidence [Song and Richards 1996] of the earth's interior.
Song and Richards 1996 paper show that the inner core rotates about 1.1° / year faster than the rest of the planet. It hardly qualifies as evidence for the dynamo model. It is caused by the reduction in the Earth magnetic field and is consistent with both models.
3. Barnes  relies on an obsolete model of the earth's interior. He views it as a spherical conductor (the earth's core) undergoing simple decay of an electrical current.
While Talk Origins is right that Dr. Barnes was using a now-out-of-date model, Dr. Russell Humphreys has built on that, resulting in Dynamic Decay Theory.
- However, the evidence supports Elsasser's dynamo model, in which the magnetic field is caused by a dynamo, with most of the "current" caused by convection.
Actually, it does not support the dynamo model.
- Observed reversal pattern in rocks do not actually fit what is predicted by dynamo model and plate tectonics.
- The dynamo model does a poor job of predicting or explaining the magnetic fields of the other planets while Dynamic Decay Theory does a good job of both.
- Barnes cites Cowling to try to discredit Elsasser, but Cowling's theorem is consistent with the dynamo earth.
This is an out-of-date claim and it is not used by creationists any more. Furthermore, the only place this claim is used is at Talk Origins and anti-creation sites cloned from it.
4. Barnes measures only the dipole component of the total magnetic field, but the dipole field is not a measure of total field strength. The dipole field can vary as the total magnetic field strength remains unchanged.
Dr. Barnes only measured the dipole, because the non-dipole portion is too chaotic to have any meaningful trend; however Dr. Russell Humphreys did measure the non-dipole portion as well and has found that it does not entirely make up for the loss in magnetic field energy in the dipole. He found that when the non-dipole portion is considered, the total magnetic field energy is decreasing with a half-life of 1465 years.