A new article in Nature Geoscience suggests that the inner core is made up of two layers. While the outer core of the Earth is liquid, the inner core is solid and composed of iron and nickel. This new study suggests that the inner core is further divided into two layers: the outer inner core and the inner inner cores. The outer inner core is has a north-south magnetic orientation, whereas the the inner inner core has a east-west magnetic orientation. Geologist believe that when the inner core solidified (0.5 - 1.5 billion years ago) it must have rolled over. Some people think this may be linked with the Cambrian explosion of life.