Selections from Earth’s Magnetic Field Is Decaying Steadily—with a Little Rhythm, by D. Russell Humphreys.
(These selections by Marko Malyj are of the article published in Creation Research Society Quarterly Journal, Volume 47, Number 3, Winter 2011, to appear at http://www.creationresearch.org/crsq/abstracts/Abstracts47-3.htm).
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The earth’s magnetic field is is the familiar two-pole (north and south) field shown in Figure 1. The strength of its source is called the magnetic dipole moment.
Four decades ago, Keith McDonald and Robert Gunst (1967, 1968) compiled the results of such measurements from 1835 to 1965. They drew a startling conclusion: during those 130 years, the earth’s magnetic dipole moment had steadily decreased by over 8 percent! Such a fast change is astonishing for something as big as a planetary magnetic field. Nevertheless, the rapid decline remained relatively unknown to the public, a “trade secret” known mainly to researchers and students of geomagnetism.
A few years later, Thomas Barnes (1971), a creation physicist, began publicizing the trade secret. Dr. Barnes’s fit (1973) to the dipole decay data he had then gave a half-life of 1365 years (time constant τ of 1970 years).
|Figure 2. Previous compilation and fit |
(Humphreys, 1983) of 34 analyses
of earth’s magnetic dipole moment
from 1829 to 1980. Large scatter mainly
due to different methods of analysis.
Time constant was 2049 (± 79) years
(half-life of 1420 years).
After Dr. Barnes fitted the dipole moment decay to MacDonald and Gunst’s compilation of data, I added newer data from the geomagnetic literature and made a somewhat more extensive fit, shown in Figure 2 (Humphreys, 1983). Even more recent and systematic data are now available, so in this paper I present a new curve fit to the new data.
A Better Compilation of Magnetic Data
In 1968 the International Association of Geomagnetism and Aeronomy (IAGA) began more systematically measuring, gathering, and analyzing geomagnetic data from all over the world. This group of geomagnetic professionals introduced a “standard spherical harmonic representation” of the field called the International geomagnetic Reference Field, or IGRF. Every five years, starting starting in 1970, they have published both dipole and non-dipole components of the field.
Using older data, the IAGA also extended the model back to the beginning of the twentieth century. With the issuance of the latest data set, IGRF-11, we have a standardized set of geomagnetic data from 1900 to 2010. You can download it free of charge as an ASCII file, a table of over 2700 numbers, from the National Geophysical Data Center website (International Association of Geomagnetism and Aeronomy, 2010). One of the IAGA authors estimates accuracies that I have used here (Lowes, 2010). The IGRF is the most consistent set of global geomagnetic data that cover such a long period of time.
Fitting a Curve to the Data
|Figure 8. IGRF-11 dipole moments |
with exponential line only.
Unexpectedly, the deviations from the straight line followed a smooth small “S”-shaped sinusoidal curve.
Possible Cause of the Sinusoid
Since the nineteenth century, geoscientists have noted a periodicity of about 60 years in the length of earth’s day (i.e., in the rotation rate of the mantle), the peak differences being several milliseconds per day (Gross, 2001). They did not find a clear connection to that in the geomagnetic data. But a recent report, confirming a 62 ± 3-year period in the length of day, found a rough correlation with the inclination and declination of the field (Roberts et al., 2007).
The six-decade sinusoid may come from a magnetically mediated mechanical east-west oscillation between the mantle and the core. This would affect the length of the day.
The sinusoid part of the curve fit in this paper appears to be the first clear indication of a 66-year periodicity in the magnetic moment. It is surprising that no one has previously detected this!
Discussion and Conclusion
The decay rate is so fast that if extrapolated smoothly more than a dozen or so millennia into the past, the earth’s magnetic field then would have been unreasonably strong. Further evidence that the earth’s magnetic field is young.
Barnes, T.G. 1971. Decay of the earth’s magnetic field and the geochronological implications. CRSQ 8:24–29.
Barnes, T.G. 1973. Electromagnetics of the earth’s field and evaluation of electric conductivity, current, and joule heating in the earth’s core. CRSQ 9:222–230.
Gross, R. 2001. A combined length-of-day series spanning 1832–1997: LUNAR97. Physics of the Earth and Planetary Interiors 123:65–76.
Humphreys, D.R. 1983. The creation of the earth’s magnetic field. CRSQ 20:89–94.
Lowes, F.J. 2010. The International Geomagnetic Reference Field: a “health” warning. http://www.ngdc.noaa.gov/IAGA/vmod/igrfhw.html.
McDonald, K.L,. and R.H. Gunst. 1967. An analysis of the earth’s magnetic field from 1835 to 1965. ESSA Technical Report IER 4 6 –IES 1. U.S. Government Printing Office, Washington, DC.
McDonald, K.L. and R.H. Gunst. 1968. Recent trends in the earth’s magnetic field. Journal of Geophysical Research 73:2057–2067.
Roberts, P.H., Z.J. Yu, and C.T. Russell. 2007. On the 60-year signal
from the core. Geophysical and Astrophysical Fluid Dynamics 100(1):11–35.