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The global absolute paleointensity (PINT) database, sponsored by the International Association of Geomagnetism and Aeronomy, recently was updated with new data and published alongside a new queryable interface at http://earth.liv.ac.uk/pint/. Absolute paleointensity determinations are spot readings of the strength of the geomagnetic field at the time and place at which a rock cooled down from elevated temperatures. The time generally can be estimated using an independent dating technique applied to the rock itself, and the place (or at least the paleolatitude) of the rock often can be estimated from the associated paleomagnetic direction.
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Biggin et al. (2010) studied this question.
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