48  The Earth’s Magnetic Field
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Most planet have their own magnetic field, also the sun. One would expect these magnetic fields to have a longer or shorter life depending on the hypotheses of the origin. Measurements of the earth’s magnetic field have indicated a continuous decrease over the last approx. 170 years. Based on these measurements, it is possible to estimate the age of the earth’s magnetic field to be less than 10,000 years old.



Magnetosphere
Magnetosphere

The earth has a solid inner core of iron surrounded by a liquid core which, for its part, is surrounded by a solid stone crust. The globe rotates causing the liquid portion of the core to move in a helical form due to Coriolis force. One can imagine that this motion has generated a dynamo which could have been responsible for development of the initially weak magnetic field of the earth (dynamo theory). However, it has not yet been possible to reproduce this with any satisfactory mathematical model. On the contrary, the measured data indicates that the earth was created with a relatively strong magnetic field which continuously decreases since (1).

The earth’s magnetic field has been measured since 1835. The measurements show that the field strength decreased by 8 % between 1835 and 1965. The various measurements allowed the conclusion that the magnetic field strength may be reduced by half every 1,465 years. Measurements performed by the geophysical observatory in Munich showed that the earth’s magnetic field has decreased for approx. 3,000 years. If it continues at this rate, it will no longer exist in 4,000 years (2).


Reversal of the poles of the earth’s magnetic field

During development of geological strata all magnetizable particles are aligned according the current effective magnetic field and fixed in this direction. It has been shown that the earth’s magnetic field has reversed its polarity at least four times in the past. This is documented in the strata. Thereversal of the poles poses additional questions and clearly shows how little reliable knowledge is available regarding the processes inside the earth.

According to common doctrine, the polarity is reversed every 250,000 years on average. This number is obtained by comparing the polarity reversal events documented in the geological strata with radiometric age determinations. However, an angular change of approx. 6 degrees per day was observed in lava flows on Steens Mountain (Oregon, USA) (3). This means the local magnetic field could have reversed its polarity within approx. 30 days at the time the lava flowed out (4).


Conclusion:

It is not possible to answer many important questions with the common dynamo theory (5), this applies particularly to the question of how the gigantic quantities of liquid iron inside the earth could have changed the direction of the magnetic flux. Was the earth’s magnetic field actually created by the rotation of the iron? The only fact which can be assumed with high probability is that the position of the poles has changed only insignificantly during the earth’s history (6).


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References:

(1) D. Russel Humphreys, The Earth´s Magnetic Field is still losing energy, CRSQ 39/1 March, 2002, P. 3–13.
(2) Geophysikalisches Observatorium in München, 3sat nano, 29. August 2002, http://www.3sat.de/nano/bstuecke/36057/index.html.
(3) R.S. Coe, M. Prévot und P. Camps, New Evidence for extraordinarily rapid change of the geomagnetic field during a reversal, Nature 374, 20 April, 2002, P. 687–692.
(4) R.S. Coe und M. Prévot, Evidence suggesting extremely rapid field variation during a geomagnetic reversal, Earth and Planetary, Science Letters 92/3-4, April 1989, P. 292–298.
(5) M.R.E. Proctor und A.D. Gilbert, Lectures on Solar and Planetary Dynamos, Cambridge University Press, 1994.
(6) Proceedings of the NATO Advanced Study Institute, "Theory of Solar and Planetary Dynamos", Isaac Newton Institute, Cambridge University, 20 Sept. to 2 Oct., 1992.
 
(Image) http://en.wikipedia.org/wiki/Earth%27s_magnetic_field
 
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