Paleomagnetism and the Age of the Earth
PREFACE (for blog) to Letter “PaleoMag”: This was written to address Stan’s issues around the observed decay in the earth’s magnetic field. Stan regarded this as very strong evidence for a young earth. Here I show the key logical fallacy in this argument.
Thomas Barnes’ young earth argument based on alleged “free decay” of the earth’s magnetic field is also debunked here. A final debunking is done for Humphreys’ alleged rapid field reversals around the time of the Noahic Flood.
This essay was originally a hard copy attachment to letter “Stan 2”, but here is presented on its own.
PALEOMAGNETISM AND THE AGE OF THE EARTH
Magnetic Field Reversals
Barnes’ Free Decay versus Dynamo Theory
Side Issue: Humphreys’ “Rapid Reversals of Magnetism at the Time of the Flood”
The measurements of the strength of the earth’s magnetic field show that it has been decaying for the last few hundred years or so. IF you assume a constant rate of decline and extrapolate backwards in time, these calculations give impossibly high values by say 10,000 years ago. The claim is therefore made that the earth must be younger than that. Young earth creationists continue to claim that this demonstrates a young earth.
The key, fatal flaw in this argument is the assumption of a constant rate of decline. There is no reason to believe that the rate of change in the magnetic field a thousand years ago or ten thousand years ago was the same as observed in the last two centuries. On the contrary, there is abundant evidence that the strength of the earth’s magnetic field fluctuates up and down, and even repeatedly reverses. Therefore we would expect it to be often increasing or decreasing in strength at any given time. The recent decline is therefore no evidence for a young earth. (Also, increases in the non-dipole component of the magnetic field have nearly compensated for decreases in the dipole component, so there has been little net change in energy).
Magnetic Field Reversals
It seems clear that the magnetic field is linked to electric currents in the metallic liquid core of the earth. Proponents of a young earth have claimed that these current were endowed at creation a few thousand years ago, and that the energy of these currents has been dissipating into heat ever since. This “free decay” theory was popularized by Thomas G. Barnes, in a 1971 article, “Decay of the Earth’s Magnetic Moment and the Geochronological Implications”, and in “Earth’s Magnetic Age: The Achilles Heel of Evolution” (1983).
Ivan Rouse, a professor of physics at Loma Linda University, evaluated this issue in Origins 10(2):66-89 (1983), and noted a number of shortcomings with the free decay theory. This article, including references, is available online at: http://www.grisda.org/origins/10066.htm
Among the shortcomings of free decay is the evidence for magnetic field reversals over the ages, which do not comport with a steadily decaying field. When liquid rock (lava or magma) cools and solidifies, the minerals can act like a compass needle, and lock into themagnetic field of the earth prevailing at that time. In Rouse’s words:
Using standard stratigraphic dating techniques combined with polarity determinations of continental rocks, the reversal time scale can be extended back (Ness et al. 1980) into the Mesozoic or to about 140 million years of conventional geologic time, as shown in Figure 7. In summary, magnetic reversals have been observed in igneous rocks on land, oceanic sedimentary rocks, deep-sea sediment cores, anomaly patterns above the ocean floor, basaltic cores from the ocean floor (Johnson et al. 1978), and even some slowly cooled, large intrusive igneous masses. The generally accepted conclusion based on this datais expressed well by Cox (1963), one of the foremost geophysicists in the study of reversals:
The abundance and distribution of reversely magnetized rocks preclude their being dismissed as rare, unexplained accidents: these rocks exist on all continents; they occur among many petrological rock types, and they constitute about half of all Tertiary and Pleistocene rocks. Moreover, their stratigraphic distribution is not random. Normal and reversed rocks usually occur in stratigraphic groups of like polarity, and in areas of late Pleistocene volcanism, the youngest group is invariably normal.
That 1963 quote from Cox predates the discovery of perhaps the most dramatic evidence of magnetic field reversals, which occur on the deep ocean floor. At the midocean ridges, magma oozes up and hardens into new crust on the ocean floor, which spreads out in both directions from that ridge, like two symmetric conveyor belts. As the crust forms at the ridges, it locks in the prevailing magnetic field direction. We now find evidence of magnetic field reversals as more or less symmetric stripes of magnetic anomalies on the ocean floor, as we track away from the midocean ridge. The figure below is taken from Rouse:
FIGURE 6. Comparison of the observed geomagnetic anomaly profile with the computed profile for the east pacific rise and with the reversal time scale derived from continental rocks. (Takeuchi and Uyeda 1967).
Barnes’ Free Decay versus Dynamo Theory
The prevailing model of earth’s magnetism among geophysicists is the “dynamo” model. In Rouse’s words, “ In the dynamo model the charge motions are envisioned to be complicated motions resulting from the interactions between a moving conducting fluid and a magnetic field. In brief, the dynamo theory states that a conducting liquid core moving in a pre-existing magnetic field produces an electric current. These moving charges are assumed to sustain and intensify the initiating magnetic field. In this way, especially with an external energy source, the earth’s magnetic field could be produced and sustained over an extended period of time….
… The physics involved in solving this problem is very difficult. Fuller (1983) puts it well when he states “The origin of the geomagnetic field remains a mystery. There is no argument that some sort of dynamo in the outer core is responsible for it, but there is little agreement as to which sort it is.” For example, the forces and energies necessary to produce the fluid motions in the dynamo are not known. The promising possibilities are (Levy 1979, Stacey 1969): 1) thermal buoyancy or convection as a result of heat produced by radioactive decay, 2) chemical separation and latent heat at the boundary between earth’s solid inner and liquid outer core, 3) different precession rates of the core and mantle, 4) gravitational energy release by shrinking of the earth as the denser solid core grows. “
When Rouse wrote his article in 1983, there were considerable unsolved problems or at least mysteries with the dynamo model. However, great advances have been made since then in understanding the physics of geomagnetism. It has been found that there are indeed differences between the rotation of the core and rotation of the mantle. The more sophisticated dynamo models can now predict the key observed features of the earth’s magnetic field, including periodic reversals, as noted in the next paragraph. This doesn’t mean every detail is resolved, but the main drivers of the earth’s magnetic field are now understood.
[from here down to the next row of astericks is an excerpt which notes advances in dynamo theory from an article by Tim Thompson, and four of his references]
On Creation Science and the Alleged Decay of the Earth’s Magnetic Field
by Tim Thompson
Copyright © 1996-2003
..[scientists] know a great deal, as a perusal of the references I gave above will show. They just don’t know everything, and cannot answer every question. Nobody knows, yet, by exactly what mechanism specific fluid motions generate the Earth’s specific magnetic field, but the presence of turbulent motions in the Earth’s fluid outer core can hardly be denied, and physical models do show that the expected velocities will, in general, generate magnetic fields…….
The most recent noteworthy results were accomplished by Gary Glatzmaier of Los Alamos National Laboratories and Paul H. Roberts from UCLA. They made use of the (now known) fact that the Earth’s inner core rotates out of sync with the rest of the planet [11a], and included this effect in their detailed model of the geodynamo. The result was a long period of stasis followed by a rapid reversal in polarity, during which the field behaved generally as the Earth’s field does during real field reversals; the energy migrates from the dipole component into the higher order components, and then reforms a main dipole, with polarity reversed. This very recent result is a major milestone in the history of dynamo theory, and is described in a trio of recent journal papers [11b, 12, 13a]. In particular, this result puts to rest once and for all, the notion advanced by Barnes, that “No acceptable dynamo theory to sustain or oscillate the earth’s magnetic field has ever been conceived nor is one very likely.” [III-I, page 49]. So much for Barnes’ bold prediction.
[11a] “Seismological Evidence for Differential Rotation of the Earth’s Inner Core” by X.D. Song and P.G. Richards. Nature 382(6588): 221-224 (1996 Jul 18).
[11b] “A 3-Dimensional Self-Consistent Computer Simulation of a Geomagnetic Field Reversal” by G.A. Glatzmaier & P.H. Roberts. Nature, 377(6546): 203-209 (21 September 1995).
” A 3-Dimensional Convective Dynamo Solution with Rotating and Finitely Conducting Inner-Core and Mantle” by G.A. Glatzmaier & P.H. Roberts. Physics of the Earth and Planetary Interiors 91(1-3): 63-75 (September 1995).
[13a] “An Anelastic Evolutionary Geodynamo Simulation Driven by Compositional and Thermal Convection” by G.A. Glatzmaier & P.H. Roberts. Physica D 97(1-3): 81-94 (October 1, 1996).
The magnetic field is driven mainly by the kinetic energy of the rotation of the earth, and convective currents from the hot (due largely to radiactivity) core, so it can be sustained for eons, with or without reversals.
Side Issue: Humphreys’ “Rapid Reversals of Magnetism at the Time of the Flood”
“The Earth’s Magnetic Field is Young” by D. Russell Humphreys
In this article, Humphreys notes a rapid decay of the magnetic field, and asserts (I doubt this) that this “was not widely known, even among scientists, until Dr. Thomas Barnes, a creationist physicist, began publicizing it in 1971”. He further asserts that mainstream dynamo theories “do not have a good explanation for the rapid decay of the field, whereas the free-decay theory does. “ However, as we have noted above, this is wrong: free-decay does not fit the data, while the dynamo theory does.
Humphreys then correctly notes that it was a mistake for young earth creationists to simply extrapolate the current rate of decay backward in time. He cites Merrill, R. T. and M. W. McElhinney. The Earth’s Magnetic Field (London: Academic Press, 1983) 101-106 for archeomagnetism data. “Archaeomagnetism” is, in Humphries’ words, “ the study of the magnetization of bricks, pottery, campfire stones, and other man-related objects studied by archaeologists. Iron oxides in those objects retain a record of the strength and direction of the earth’s magnetic field at the time they last cooled to normal temperatures. Archaeomagnetic data taken worldwide show that the intensity of the earth’s magnetic field was about 40% greater in 1000 A.D. than it is today, and that it has declined steadily since then.”
So far, so good. But he further claims that these data show rapid field reversals in the third century B.C., which (according to a literal reading of Genesis, with creation around 4000 B.C.) would be the time of Noah’s flood (~2500 B.C.). This would appear to be potent support for young earth creationism.
Joe Meert, a Christian geologist, has dug into the actual data behind this figure. He discusses this in http://www.theologyweb.com/campus/archive/index.php/t-6500.html
Note that the relevant discussion is way down in the dialog on this link; I’d suggest searching on “magnetic” or “Humphreys” to find it faster.
Meert debunks a number of the usual young earth myths (not enough mud on the sea floor, not enough sodium in the sea, etc.). About the Humphries’ decaying magnetism claim, Meert states:
This one is based on a misrepresentation of archeomagnetic data he proposed in one of the ICR impact series. Humphreys completely fabricated the notion of rapid reversals of the field (Since archeomagnetic data show no reversals)! Furthermore, the strength of the dipole field does fluctuate and change through time. Currently, it is decreasing, but the field is still much higher than it has been in the past. Just because an explanation is complex, it does not mean it is wrong. In fact, the complex theories for the Earth’s magnetic field are based on real data. Humphreys ‘theory’ is based on a misrepresentation of archeomagnetic data (e.g. drawing reversals and zero lines on a curve that shows neither)……
If we look up reference number 7, we find it refers to Merrill, R. T. and M. W. McElhinney. The Earth’s Magnetic Field (London: Academic Press, 1983) 101-106. On pages 101-106 of that book there are two graphs and one data table. None of the data show a reversal, but one graph looks like a mirror image of Humphreys Figure 1. … (note this is a compilation of Australian aboriginal sites and NOT the whole world. …Now Humphreys has claimed that his figure is conceptual and based loosely on the 500 year averages in the book. The 500 year averages are shown below:
[I copy this figure here:]
I’ll let the reader decide if there is a zero-crossing (required for a reversal) or if Humphreys model is a better fit to the data. Note that there are no ‘wild fluctuations’ observed in the archeomagnetic database using 500 year averages and that today’s field is actually stronger than it has been in the past. Thus, while the dipole field shows a decreasing intensity, it is still greater than 6000 years ago and therefore (using the young earth timeline) stronger than at creation.
In other words, the actual dipole data do fluctuate, but do not show the “reversals” (dropping below a zero line and going negative) asserted by Humphries. As is common in these on-line exchanges, a young earth creationist attacks Meert personally, accusing him of being an “infidel”, “bigoted against the Bible”, and “attacking inspiration itself.” Meert replies,
Nope, I’m not bigoted against the bible. However, your personal attack is noted. The bible is a truly wonderful book about history, poetry, allegory and most importantly, salvation. You should read it sometime without trying to force it to fit to your idolatrous viewpoint. I forgive you bearing false witness. Anger sometimes gets the best of me too. Keep praying for God to soothe your bitterness…..The bible is not a science book. The sooner you realize that, the less angry and bitter you’ll be and the more insight you’ll gain about salvation.
Here is a more formal article “Is the Earth’s Magnetic Field Young?” by Joe Meerts, again debunking Humphries’ field reversal claims above, and also debunking claims of rapid field reversal in the Steens Mountain basalt flows.
COPYRIGHT SCOTT BUCHANAN 2010
Permission is granted for reproduction for non-commercial use as long as the contents are not altered and attribution is given.