THE Grand Canyon in Arizona has a bizarre Antipodean link. A chunk of the rock sequence that has been sliced through to form this natural wonder of the world now sits thousands of kilometres away in Tasmania, Australia.
To peer into the Grand Canyon is to behold, in its rock layers, a record of Earth’s distant past. The oldest layers at the bottom date back more than 1.5 billion years.
It is some of the most ancient layers in the sequence that interest Jack Mulder, a geologist at Australia’s Monash University. He thinks these rocks – which are between about 1.1 and 1.2 billion years old – look just like similarly ancient rocks in Tasmania.
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The Tasmanian rocks in question have always seemed a bit out of place, he says. “They didn’t look a lot like similarly aged rocks nearby.”
Mulder and his colleagues have now found that the rocks contain minerals with the same “geochemical fingerprint” as those in the Grand Canyon (Geology, ).
“We concluded that although it’s now on the opposite side of the planet, Tasmania must have been attached to the western United States,” he says.
“We concluded that Tasmania must have been attached to the western United States”
Beyond extending the Grand Canyon’s reach across the Pacific and into the southern hemisphere, uniting the Tasmanian rocks with those in North America helps to solve an ancient geological jigsaw puzzle.
About a billion years ago, all of Earth’s continental plates formed a single supercontinent called Rodinia. But working out exactly how today’s continents would once have fitted together to form Rodinia is no simple task given how long ago it existed. The Tasmanian discovery provides a clue because it is clear evidence that North America and Australia were linked together at the time.
“Jack’s paper shows that Tasmania holds the key to tying together the tectonic geography of the time,” says Alan Collins at the University of Adelaide, Australia. “It’s really a good link and tie that allows us to build full plate models of the ancient Earth.”
This article appeared in print under the headline “Australia’s Grand Canyon connection”
