North America and Australia are practically on opposite sides of the world today, but some 1.7 billion years ago, they may have been joined at the hip.
The surprising revelation comes after geologists discovered extremely old rocks in northeast Australia with signatures that have a striking resemblance to similarly-aged rocks found in Canada today. The find represents mounting evidence that these two distant lands were once connected.
How could this have been possible? We know that Earth's continents are constantly on the move due to plate tectonics, but even when geologists trace back the paths of Australia and North America to the last time all of the continents were connected as part of the supercontinent Pangea, these landmasses were still never joined. So, if Australia and Canada ever did share a border, it had to have been even longer ago — far further back in history than Pangea.
In fact, that's exactly what scientists now believe. About 2.5 to 1.5 billion years ago, the planet's continents were also arranged as a supercontinent known as Nuna. It was at this time that a chunk of modern-day North Queensland, Australia, was bumped up against Canada's Hudson Bay region.
"This was a critical part of global continental reorganization when almost all continents on Earth assembled to form the supercontinent called Nuna," explained PhD student Adam Nordsvan from the School of Earth and Planetary Sciences at Curtain University, where the research was conducted, in a press release.
Interestingly, scientists suspect that an ancient mountain range would likely have once existed along this North American-Australian border, which would have formed when the two continents first collided.
"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," said study co-author, Zheng-Xiang Li.
He continued: "This new finding is a key step in understanding how Earth's first supercontinent Nuna may have formed, a subject still being pursued by our multidisciplinary team here at Curtin University."