Well, OK, it’s not that the canyon itself is partly in Australia, but the rock formations through which the canyon was formed are partly in Australia.
How do we know? Many of those rock layers with their very distinctive and unique sequences and chemical compositions have also now been found in Tasmania, the large island just south of the Australian state of New South Wales. It’s the oldest rocks of the Grand Canyon series that have been discovered in Tasmania. The rocks have always seemed unrelated to other rocks in the same part of the island, but they look like the oldest canyon rocks in many of their details and make-up.
The solution to this puzzle can only be that part of Australia was once a single piece of continental crust with the rocks of the Grand Canyon. That would have been way back a thousand million years ago when the super-continent Rodinia existed. Since then, the continents have broken apart, moved around, run into one another, and broken apart again. The breakup of Rodinia separated the early rock grouping into pieces that became part of modern North America and Australia.
This is not a new theme in the history of the continents. In a much more recent episode (the opening of the Atlantic Ocean) an ancient mountain chain was torn in two; the parts now form the Appalachians in North America and the Scottish Highlands on the edge of Europe.
But this new discovery helps scientists put more detail into the very early story of continental crustal movement and break up. Thanks to Jack Mulder and others for publishing the discovery and New Scientist for sharing the story more widely.