Earth’s next supercontinent has already begun to form. Most school kids have learned about Pangea (meaning “all lands”) which contained about 80% of Earth’s continents locked together in one landmass. Pangea began to break up about 180 million years ago with the opening of the Atlantic Ocean. But a new supercontinent has since started to form.
Looking at the continents scattered around the globe today, one can’t help but notice that one continent is larger than the others: Eurasia. Australia is also currently on a tectonic collision course to someday join Eurasia and end up somewhere between Japan and India, which would make Eurasia even bigger. So why does Eurasia’s size stick out?
According to an article recently published in GEOLOGY, Eurasia constitutes what is referred to as a “megacontinent”: a significant precursor that forms about 200 million years before the larger supercontinent finally amalgamates. The international team of researchers led by IGGCAS was able to identify the existence of such a megacontinent associated with each known supercontinent cycle over the past 2 billion years.
"We know of three supercontinents, and they were all preceded by a megacontinent. Therefore, the assembly of Eurasia, yet another megacontinent, portends the formation of the next supercontinent,” explained lead author and IGGCAS post-doctoral researcher Dr. Chong Wang.
Gondwana is perhaps the next best known megacontinent as it constituted the southern and larger half of Pangea. Previously, there was great debate over the significance of Gondwana, with some geologists referring to it as a supercontinent and others arguing against that notion as it eventually became part of the larger Pangea. To address this stalemate, the IGGCAS-led research looked for clues about the assemblies of both Eurasia and Gondwana. Images generated with seismology of Earth’s deep mantle indicate that Eurasia assembled where the convection in the underlying mantle is flowing downward.
"If you pull the plug in a bathtub, all floating objects will migrate towards the downwelling flow of water. Similarly, continents will migrate and collect where downwelling flow in the underlying mantle is most intense,” explains co-author and IGGCAS Professor Ross Mitchell.
This migration towards the zone of downwelling can also explain why all the continents (with the sole exception of Africa) are currently distributed along the “ring of fire” surrounding the Pacific Ocean. The “ring of fire” is where most volcanoes and earthquakes on Earth are found due to the concentration of Earth’s subduction zones along it. Subduction—how plate tectonics recycles oceanic crust back down into the mantle—typically occurs where mantle convection is directed downward.
"Eurasia formed where it did because this is where the downgoing mantle flow is most intense along the ring of fire. But because the mantle is downwelling all along the ring, this gives us our next clue as to how a megacontinent evolves into a supercontinent,” says Dr. Wang.
As Eurasia is still forming and the evolution to the next supercontinent is incomplete, the researchers also needed a clue from the completed transition from Gondwana to Pangea. Using plate tectonic reconstructions, the team showed that eventually the other continents of Pangea amalgamated with Gondwana by assembling along the ancient ring of fire.
Professor Zheng-Xiang Li of Curtin University, who was not directly involved in the study, notes “that the two-step process to assemble a supercontinent advocated by the authors, in addition to breakup, adds a new dimension to our understanding of the supercontinent cycle.”
"Rome wasn’t built in a day, and neither is a supercontinent. A megacontinent is a critical early building block from which the larger supercontinent is built,” said Professor Mitchell.
The article is open-access and available at https://doi.org/10.1130/G47988.1.
SCIENCE news reports this research at https://www.sciencemag.org/news/2021/01/what-might-earth-s-next-supercontinent-look-new-study-provides-clues.