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Researchers Find a Chunk of North America Stuck to Australia

When an ancient supercontinent broke apart the Queensland peninsula may have gotten left behind

(Reto Stöckl / NASA Goddard Space Flight Center)
smithsonian.com

Anyone who's taken the epic plane flight from North America to Australia knows that Oz is very, very far away. But that wasn't always the case. And a new study suggests that the northern tip of Queensland, Australia was actually once a hunk of North America, reports Naaman Zhou at The Guardian.

Geologists from Curtin University in Perth, Australia, examined rock samples from the area around Georgetown in northern Queensland. Their analysis suggests that these rocks have chemical signatures very different from rocks found in the rest of Australia, and are quite  similar to rocks found in Canada.

The new study, published in the journal Geologysuggests that the reason behind these differences is the movements of an ancient supercontinent, even older the commonly known Pangaea, which existed between 335 and 175 million years ago. The sediments that make up these rocks were likely deposited in shallow seas that existed in North America around 1.7 billion years ago. But sometime after their deposition this "ribbon" of land, which is the present-day Georgetown in Australia, broke off.

During this time, almost all the continents were drifting together in what would eventually be known as the supercontinent Nuna, lead author and Curtin PhD candidate Adam Nordsvan explains in a press releaseRoughly 1.6 billion years ago​​, as they drifted ever closer, Georgetown collided with the Mount Isa region of Northern Australia. When the future North America and Australia came apart, around 1.4 billion years ago, the Georgetown region remained stuck down under.​

Though most people have heard of Pangaea, which was the last massive land formation that existed, researchers have proposed quite a few other supercontinents that formed and split during Earth's long history. The earliest of these mash-ups included Ur and Vaalbaara, but both of these are fairly speculative, Alasdair Wilkins wrote for i09 in 2011. Next up in the supercontinent timeline is Kenorland, followed by Columbia (also known as Nuna), Rodinia, Panottia and Pangaea. In fact, according to Wilkins, plate tectonics will likely smoosh all of Earth's landmasses into another supercontinent in about 250 million years.

All of this smashing together time and time again means fragments of these continents often get displaced—pieces break off, stick together, rise as mountains or become part of the seafloor. So it's not too surprising that Nuna left behind its mark on Australia. As Nordsvan tells Zhou, the current paper only looks at a sample of rocks from Georgetown, but he thinks data collected later this year will likely show that the entire Queensland Peninsula was once part of North America.

Since the 1970s, researchers have believed that there was a link between North America and Australia, Zhou reports, but they didn't have enough data to prove it. “On the North American side, some great research has come out showing the connection was likely at that time [of Nuna],” Nordsvan says. “In Australia there has been a little bit of research that shows the connection was likely there. This is probably the first piece of really good evidence that at 1.7bn or 1.6bn years ago, there was definitely a connection between the two continents.”

The mountains around Georgetown also tell researchers a little bit about the how Nuna formed so many millions of years ago. “Ongoing research by our team shows that this mountain belt, in contrast to the Himalayas, would not have been very high, suggesting the final continental assembling process that led to the formation of the supercontinent Nuna was not a hard collision like India’s recent collision with Asia,” co-author Zheng-Xiang Li says in the press release. “This new finding is a key step in understanding how Earth’s first supercontinent Nuna may have formed.”

Queensland is not the only place with a piece of another continent attached. The Florida Peninsula was once part of present-day Africa. A small bit of crust called the Suwannee Terrain from northwestern Africa crashed into North America 200 million years ago forming the underlying rock of the Sunshine State.

About Jason Daley

Jason Daley is a Madison, Wisconsin-based writer specializing in natural history, science, travel, and the environment. His work has appeared in Discover, Popular Science, Outside, Men’s Journal, and other magazines.

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