Scientists have discovered a giant metallic ball at the centre of the Earth

Earth has another layer in the form of a solid metallic ball at it's centre, scientists have discovered in a new study.

Before, it was thought the Earth's layers was made up of four layers: the crust, mantle, (liquid) outer core and (solid) inner core.

Now, an "innermost inner core," was found by a team of two seismologists from the Australian National University, Thanh-Son Phạm and Hrvoje Tkalčić, who believe the 400-mile (in diameter) metallic ball may have been formed following a "significant global event from the past."

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As part of the research, around 200 earthquakes and tremors across the last decade were studied in order to understand how fast the seismic waves passed through the inner core of the earth.

While the metal inner core contains the same material as the molten core, scientists believe the inner core also has different properties which affects how fast seismic waves travel through it.

"Clearly, the innermost inner core has something different from the outer layer," lead author Thanh-Son Pham, a seismologist at the Australian National University, told The Washington Post.

"We think that the way the atoms are [packed] in these two regions are slightly different."

Scientists also found the metal ball has a crystal structure that differs from the other layers.

Both researchers believe the metal inner core could be a "fossilised record" of a significant tectonic event, that could help us further understand how life evolved on this planet.

“Studying Earth’s center is not just a topic of academic curiosity, but something that sheds light on the very evolution of life on our planet’s surface," the pair said in an article for The Conversation.

This study has been published in the journal Nature Communications.

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