CANBERRA, AUSTRALIA — Traditionally students have been taught that the Earth has four distinct layers: the crust, the mantle, the outer core and the inner core.

Now, a new study by researchers from the Australian National University provides evidence of an additional layer inside the inner core.

According to the study, which was published in the Journal of Geophysical Research, the inner core is made primarily of iron and nickel. The innermost core is composed mainly of iron and is around two-thirds the size of the Moon.

The authors of the study write this suggests that some sort of cataclysmic and previously unknown event occurred early in the Earth's history — perhaps as early as 4.5 billion years ago.