Geomagnetic intensity as evaluated from ancient Chinese pottery

Abstract

Past values for the geomagnetic intensity may be obtained by laboratory analysis of the thermoremanent magnetization carried by clay baked in ancient times. From global averages1–3 of such determinations it is commonly accepted that the intensity in any given region went through a broad maximum about 2,000 years ago, reaching a level 50% higher than at present. Here we present results obtained from a wide range of Chinese pottery, spanning the interval from 4000 BC to the present, indicating that the field behaviour was more complex. The intensity was high between 1500 and 1000 BC and again in the first half of the first millennium AD. Comparison with results reported4,5 for Western Asia, Egypt and Crete suggests that these high values are due to non-dipole disturbances in the geomagnetic field, consistent with long-term records6–8 of the cosmogenic radioisotopes 14C and 10Be.

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References

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