About 200 million years ago, the supercontinent of Gondwana—essentially an an agglomeration of Africa, South America, India, Australia and Antarctica—began slowly ripping apart into the continents recognizable today. But a new study suggests that Gondwana spun out another continent that is now lost beneath the Indian Ocean.
As Alice Klein reports for New Scientist, researchers studying the earth’s crust found that parts of the Indian Ocean's seafloor had slightly stronger gravitaitonal fields, suggesting that the crust might be thicker there.
The island of Mauritius exhibited this extra oomph, which led Lewis Ashwal, a geologist at the University of the Witwatersrand, South Africa, and his colleagues to propose that the island was sitting atop a sunken chunk of continent.
The researchers studied the geology of the island and rocks spewed out during periods of ancient volcanism. One particular mineral they were looking for are zircons, tough minerals that contains bits of uranium and thorium. The mineral can last billions of years and geologists can use these to acurately date rocks.
The search paid off. The researchers recovered zircons as old as 3 billion years, Ashwal says in a press release. But the island rocks are no older than 9 million years old. The researchers argue that the old rock is evidence that the island is sitting on a much older crust that was once part of a continent. The zircons are remnants of this much older rock and were likely pushed up by volcanic activity. They published their results in the journal Nature Communications.
According to Paul Hetzel at Seeker, researchers had previously discovered zircons on Mauritius' beaches, but were unable to rule out the possibility that they were brought there by the ocean. The new finding confirms that the zircon comes from the island itself.
Mauritia was likely a small continent, about a quarter the size of Madagascar, reports Klein. As the Indian plate and the Madagascar plate pulled apart, it stretched and broke up the small continent, spreading chunks of it across the Indian Ocean.
“According to the new results, this break-up did not involve a simple splitting of the ancient super-continent of Gondwana, but rather, a complex splintering took place with fragments of continental crust of variable sizes left adrift within the evolving Indian Ocean basin,” Ashwal says in the press release.
Klein reports that other islands in the Indian Ocean, including Cargados Carajos, Laccadive and the Chagos islands might also exist on top of fragments of the continent now dubbed Mauritia.
Surprisingly, this may not be the only lost continent out there. In 2015, researchers at the University of Oslo found evidence that Iceland may sit on top of a sunken slice of crust. And in 2011, researchers found evidence that a micro-continent has existed off the coast of Scotland for about a million years.