Around 155 million years ago, a huge chunk of Western Australia broke off and drifted away – and has only just been found again.
Scientists know the 5,000km piece of land existed because of a massive hole it left behind on the ocean floor, known as the Argo Abyssal Plain.
From here, telltale signs under the sea suggest it drifted northwest to the islands of Southeast Asia, but no trace has ever been found.
One theory suggested that the continent, newly named Argoland, could have disappeared entirely by being sucked back into Earth’s mantle – the molten layer beneath the crust – where two tectonic plates meet. This was the case for part of another ‘lost’ continent, Greater Adria, a ‘paleomicrocontinent’ about the size of Greenland that broke off from Italy.
However, Greater Adria still left traces of itself in layers of rock that later formed the mountains of Southern Europe, whereas there are no such signs of Argoland in the mountains of Southeast Asia.
Now however, fragments of the continent have been found hiding beneath the many islands of the region, suggesting it splintered as it went, rather than travelling in one big lump.
‘If continents [could] dive into the mantle and disappear entirely, without leaving a geological trace at the earth’s surface, then we wouldn’t have much of an idea of what the Earth could have looked in the geological past,’ said co-author and Utrecht University professor Douwe van Hinsbergen.
‘It would be almost impossible to create reliable reconstructions of former supercontinents and the earth’s geography in foregone eras.’
Digging into the layers of rock from islands across Southeast Asia, including Sumatra, Borneo, Sulawesi and Timor, Professor van Hinsbergen and lead author Dr Eldert Advokaat combined their findings with computer simulations of tectonic and continental movements.
The results suggest that around 250 million years ago Argoland began to fracture and splinter, the remnants of which are now hidden deep beneath the lush jungles of the region’s thousands of islands.
‘We were literally dealing with islands of information, which is why our research took so long. We spent seven years putting the puzzle together,’ said Dr Advokaat.
‘The situation in Southeast Asia is very different from places like Africa and South America, where a continent broke neatly into two pieces. Argoland splintered into many different shards. That obstructed our view of the continent’s journey.’
The findings, published in the journal Gondwana Research, also fit with the original model of Argoland, which was more an ‘Argopelago’ or different land masses than a single area.
The puzzle that Advokaat and Van Hinsbergen have solved fits seamlessly between the neighbouring geological systems of the Himalayas and the Philippines, and adds another chapter to the long story of Earth’s jigsaw of continents.
Around 230 million years ago, as dinosaurs began to roam the land, the continents as we know them today were arranged in a single supercontinent called Pangea. This slowly broke apart, shuffling the land around like pieces on a chess board until they formed the world seen today.
However, the continents are still moving. North and South America drift away from Europe and Africa by about 2cm a year, while the Himalayas grow around 1cm a year as India continues to move north, scooping up the rock in front of it.
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