The Tasmanian rocks that were once part of the Grand Canyon (Image: Jack Mulder)
The rocks in the Grand Canyon provide a record of Earth’s distant past, with the the oldest layers at the bottom dating back more than 1.5 billion years. Jack Mulder, a geologist at Australia’s Monash University, realised that some of the canyon's oldest rocks, which are between about 1.1 and 1.2 billion years old – are very similar to rocks of the same age in Tasmania. He says that the Tasmanian rocks in question have always seemed a bit out of place, as they don’t look a lot like similarly aged rocks nearby.
Mulder and his colleagues have now found that the Tasmanian rocks contain minerals with the same “geochemical fingerprint” as those in the Grand Canyon (Geology, doi.org/cv24). They have concluded that, although it’s now on the opposite side of the planet, Tasmania must have at one time been attached to the western United States.
This identification of the Tasmanian rocks with those in North America helps to clarify an ancient geological jigsaw puzzle. About a billion years ago, all of Earth’s continental plates formed a single supercontinent called Rodinia. But the task of working out exactly how today’s continents would once have fitted together to form Rodinia is not simple because of the long time gap since Rodinia 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 story is based on an article in New Scientist.
Bill Gray