Posted by: paulgarner | October 12, 2009

Geomagnetic confusion

It’s time to eat humble pie. A sharp-eyed reader of my book, The New Creationism, has contacted me to point out that the labels on the figure illustrating the earth’s magnetic field (p.190) are not really right. Here’s the offending diagram. The field lines are correct but the image of the bar magnet has the poles the wrong way round.

Geomagnetic field

The reason is that the magnetic north pole in fact has the polarity of a south magnetic pole. That’s why it attracts the north-seeking pole of a compass needle. Strictly speaking, then, the bar magnet in the diagram ought to have its poles labelled the other way round.

To be fair, some other diagrams of the geomagnetic field, such as this one on a National Oceanic and Atmospheric Administration (NOAA) site, use the same labels as my book. However, I accept that this isn’t really correct and if and when there’s a second edition it’s something I’ll look at again.

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Responses

  1. This is an easy mistake to make, and one I may not have caught. I haven’t read your book (I’ll buy a copy some time after I get a job) so I don’t know your complete argument. I have felt for a long time that the whole “decaying magnetic field” argument of the young-Earth creationists was invalid. Earth’s magnetic field fluctuates (and even reverses), and all we see in the past few hundred years is a small portion of a rather erratic sinusoidal curve. The field evidence is certainly in favor of fluctuation and reversal rather than decay and I cannot fathom how creationists can justify using this as evidence for a young Earth.

    With respect,
    Kevin N

    • Hi Kevin,

      The context of the diagram in my book is a discussion of geomagnetic reversals as evidenced in ocean floor and continental basalts, rather than a discussion about the age of the earth. But I’m sure you won’t like the idea that the reversals occurred rapidly during an episode of catastrophic plate tectonics associated with the global flood!

      Best wishes,

      Paul

  2. Paul,

    You are right — I don’t really see how either ocean floor basalts or continental basalts fit in the global flood scenario.

    Plate tectonics works fine at a few centimeters per year, but I see problems with seafloor spreading at a rate of kilometers per day. Basaltic magma extruded along the mid-ocean ridge would certainly develop a crust on it in contact with cold seawater, but the underlying oceanic crust (about 5 km thick) would crystallize at a slower rate and would not have sufficient strength to be either pushed, pulled, or carried on top of the underlying lithospheric portion of the plate.

    Continental basalts, such as the Columbia River Basalts (CRBs), also pose problems for the young-Earth models. I’m assuming that being Miocene/Pliocene, you view the CRBs as being post-flood. A few flows record geomagnetic reversals, but most of them are either completely normal or completely reversed polarity. There is little evidence here for rapid reversals as proposed by the flood geologists. Additionally, there is plenty of field evidence in the CRBs that a considerable amount of time passed between flows, such as formation of deep tropical soils (laterites) and interflow lake and stream deposits. I cannot see fitting this into a few hundred years after the flood.

    • Again, you ask some great questions. I talk a bit about the evidences for rapid sea floor spreading and rapid geomagnetic reversals in my book. The patchiness of the magnetization of the ocean floor and the extraordinarily rapid field changes recorded in CRB flows at Steens Mountain in Oregon, described by Coe and Prévot (1995), may be taken to support rapidity. However, you raise an interesting point concerning the strength of the diverging oceanic plates and I’d like to ask my colleagues what they think about that. It’s not a subject that I can comment on with any real insight, and I’m not aware that anyone has tried to model the behaviour of the plates during CPT. But it sounds like an interesting project for someone with the right expertise.

      Your assumption that I think the Columbia River Basalts are post-flood is correct. There is evidence of the passage of time between some CRB flows, though it’s by no means clear from my reading of the literature that the time involved must have been very great. Some thick sections seem almost entirely to lack evidence of soil development, erosion or intervening clastic sedimentation. Based on their own field studies, Woodmorappe and Oard (2002) suggested that lateritic horizons in the CRB are uncommon and may be the product of hot lavas interacting with water-saturated sediments or standing water, rather than true palaeosols. (Note that I don’t agree with these authors about their designation of the CRB as late flood deposits.)

      This discussion also reminds me of a paper by Branney and Suthren (1988) that I read many years ago. They reinterpreted a number of ‘weathered lava flows’ in the Ordovician Borrowdale Volcanic Group of the English Lake District as sills that had never been exposed at the surface. They proposed that the ‘weathered’ surfaces were in fact caused by peperitic interactions between the intruding magmas and the wet sediments into which they were emplaced.


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