Dear Caroline and Jack,
The mental picture I gave was as a simple one to explain how the anomalies
occur. Conductive rocks are usually in strata which can be likened to a bunch
of separate conductors. If you bore through them, and depending on how many
separate conductive rock strata you bore through, you could mistakenly
believe the earth's magnetic field has flipped several times. Bore a bit
further and Ooops! another flip and the guy with the deepest bore in the most
stratified regions of the earth will find more magnetic flips than the guy
with a shallow bore. Also, volcanic activity can throw up rocks from deep
within the earth which will add to the confusion.
Electric currents in these rocks produce the earth's magnetic field and
changes in these currents due to extraterrestrial events cause variations in
the earth's magnetic field.
Does anyone have other evidence of magnetic flip?
Hope this clarifies matters.