In 2015, Prof Xiaodong Song from the University of Illinois and other researchers in China suggested the inner core has two layers. The seismic wave data suggests that crystals in the "inner inner core" are in an east-to-west direction. Those in the "outer inner core" are lined up north to south. Another scientist commented: "If this is true, it would imply that something very substantial happened to flip the orientation of the core to turn the alignment of crystals in the inner core north-south as is seen today in its outer parts". Other scientists are checking their data.