In 1929, ArthurHolmesshowedthermalconvectioninthemantlecouldcreateenoughof a currenttomovethecontinentalcrustontopofit, anideaheoriginallygotfromWegener.
In 1962, geologistHarryHessfound a strangemagneticpatternalong a seafloorridge.
Earth's magneticfieldhasflippedhundredsoftimeovertheplanet's history.