Excursions in geomagnetism

摘要

The intensity of Earth's magnetic field varies on timescales varying from sec-onds to many tens of millions of years. Secular variation in the field, in terms of 100-1,000 years, can be estimated from historical records. But identifying variation on longer timescales requires continuous palaeomagnetic records from much deeper in the past, and in 1996 Guyodo and Valet provided an analysis of 17 palaeointensity records going back 200,000 years. They integrated them into the so-called 'Sint-200' composite curve, which has since served as a standard. But it still covers only a comparatively brief period of Earth history.