The migrations of the continents

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The migrations of the continents
The migrations of the continents

The migrations of the continents

A growing body of evidence suggests that the landmass we know as Australia was once connected to North America on the Yukon River before the two drifted apart about a billion years ago. It sounds far-fetched considering the thousands of kilometers that separate the two continents today. But on a geologic timescale, it's easily possible, says Derek Thorkelson, a professor of geosciences at Simon Fraser University. He is just completing a five-year study that provides compelling evidence for the Yukon/Australia connection.

Thorkelson focused on a series of unusual rock formations known as breccia. They can be found scattered over 3500 square kilometers in the Wernecke Mountains. Because these formations - some of which are several kilometers long - are strikingly different in appearance from the surrounding rocks, geologists have long puzzled over their origin.

Thorkelson's study included extensive geological mapping, geochemical analysis and evaluation of minerals in the area. It shows that the breccia were formed by a series of underground explosions resulting from violent expansions of gases. "This process is fairly well understood and is not uncommon," says the scientist. "But in this case, the formation of the breccia led to the precipitation of important ores such as copper, gold, cob alt and uranium."

The Yukon breccia turned out to be identical to the subsurface breccia in South Australia. That's where the giant Olympic Dam mines are located, where gold and copper occur. Hoping that the two rock types would match, Thorkelson sent samples from the Yukon to a laboratory at the University of Alberta for dating. And indeed, both breccias are roughly 1.59 billion years old. "This Yukon/Australia connection was proposed about 10 years ago," says Thorkelson, "but there was no age determination that did any good. With this new information, we're able to make a direct correlation."

It is not without reason that the minerals in the Wernecke Mountains have been researched more intensively in recent years. Thorkelson points out that there are other geologic clues that point to a connection between the Yukon and Australia. There is even speculation that a third continent, Antarctica, was part of the puzzle.

Are you still skeptical? Don't forget, says Thorkelson, that the Earth is estimated to be around 4.5 billion years old. Movements of the earth's crust - the so-called plate tectonics - probably began three billion years ago. In contrast, the separation of North and South America from Europe and Africa, which formed the Atlantic Ocean, took place only 200 million years ago."In 1.6 billion years there could have been numerous openings and closings of ocean basins," he says. "North America and Australia may have been involved in several continental collisions and separations between then and now.

"In a geological sense, it's not remarkable at all that these continents were joined together. The interesting thing is to find out where they once were connected."

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