In the 1940s and 1950s, technology had advanced to the stage at which paleomagnetic fields from the geologic past could be measured with some reliability from rocks. Just as Wegener's geologic work identified where the geographical poles had been in the geologic past, that of geophysicists was starting to determine where the magnetic poles had been located. The alignment of a magnetic mineral in a cooled igneous rock points to the magnetic north pole, and the dip of the mineral reveals how far the rock formed from the pole. The paleomagnetic evidence revealed that the magnetic poles also had different locations relative to the continents than they do today. Magnetic minerals on one continent do not point to the same pole position as do those from the same time period on another continent. This would suggest either that there were multiple north poles during the same time period or that the continents moved in relation to a single north pole. Geophysicists concluded that the magnetic poles remained stationary, and the continents, after splitting apart, diverged along different paths.