“The iron alloys in the solid inner core of the Earth appear to have crystallized in such a way that it’s easier for energy to pass on the north-south axis than on the east-west, as described in a new study led by Maurizio Mattesini, a geologist at the Universidad Complutense de Madrid, which appeared in the journal Proceedings of the National Academy of Sciences.”  Here is the abstract.  Subscription is required to read the whole thing. I guess this is old news from 2010.