The supercontinent caused the Earth’s mantle to split in two

The Earth’s mantle is split by the Pacific Ring of Fire, an ancient structure that reflects the formation and destruction of the supercontinent Pangaea. One side contains most of the land on Earth. Named Africa, this region extends from the eastern coastal regions of Asia and Australia to Europe, Africa and the Atlantic Ocean on the western coastal regions of North America. The remainder is the Pacific region, including the ocean of the same name. Under the African region, the mantle contains many elements and their isotopes with a greater diversity than much of the Pacific region, according to Live Science.

That reflects the last two supercontinent cycles in the past billion years, according to study co-author Luc Doucet, a PhD student in Earth and planetary sciences at Curtain University in the UK. During that time, two supercontinents existed, the first being Rodinia (formed about 1.2 billion years ago and broke up 750 million years ago), and Pangaea (formed about 335 million years ago and broke up broke 200 million years ago). “What we observe now is essentially what happened during the transition from Rodinia to Pangaea and then Pangaea, breaking up,” Doucet said.

These supercontinents are united in Africa. As the ocean closes between them, the oceanic crust slides beneath the continents in a process called subduction, sometimes dragging down continental rocks with it. This activity brought elements and isotopes from the continental crust down to the mantle beneath the growing supercontinent, Doucet explains. That geological conveyor belt continued in a slightly different form after the birth of the supercontinent. The oceanic crust at the edge of Rodinia, and later Pangaea, sank beneath the continental crust, eroding some of the continental rocks. The process creates a funnel-shaped effect.

Even after Pangea broke up, signs remained in the shallow and deep mantle, according to research results published in the journal Nature Geoscience. Doucet and Zheng-Xiang Li, emeritus professor at Curtin University, focused on shallow mantle magmas in the new study. They examined 3,983 samples from mid-ocean ridges, where tectonic plates are spaced apart and magma from the shallow mantle surges up, hardening into volcanic rock or basalt.

The team then used machine learning to compare the elemental and isotopic composition of basalt samples from around the world and from the same period. Similar to magma from the deep mantle, they found that the shallow mantle divides into the African and Pacific regions. The findings reveal more about the processes that bind the mantle to the ground.