In what looks like a case of a jigsaw mishap on a tectonic scale, a team of researchers led by Curtin University (CU) has found a piece of North America – specifically, Canada – in northern Australia. This means that part of Australia was attached to and was part of North America, around 1.7 billion years ago.
While this may seem odd, and is quite a striking find for geologists, it’s not all that bizarre. Remember, on human timescales, the continents seem like unmoving colossi, but to the planet, they’ve been moving around like flotsam on an ocean.
The world was not what it once was, quite literally. Although a higher internal temperature pushed tectonic plates around somewhat more aggressively than is currently observed, the process of plate tectonics has remained largely unchanged for several billion years.
Once upon a time, there was a continental mass named Laurentia. Some of its rocks are 4 billion years old, and it’s been in a (relatively) single unified piece for just over a billion years. This stable, ancient piece of the crust now forms the geological core of North America, and much of it makes up what we recognize as Canada today, but it wasn’t always there – it’s been up and down this world, joining supercontinents and breaking away from them time and time again.
Weirdly, according to recent mapping by this particular team, the North Australian Craton has also got segments of Laurentia in it too. Not very many, mind you – potentially a few segments of the spikey top of Australia, and, rather adorably, the rock beneath Georgetown, in Queensland, which has a population of no more than 250 people.
A careful new dating analysis of the rocks there seem to match them up with those found in Laurentia, dating back to the Proterozoic eon, between 2.5 billion and 541 million years ago. So how on Earth did they get there?
According to the Geology paper, the rocks beneath Georgetown – the Georgetown Inlier – were originally part of western Laurentia. In fact, for some time, everything was stuck together.