Geologists have pieced together an uncertain part of Earth’s ancient history. A team in Australia has found new evidence that suggests the cycle of supercontinents forming and breaking up only started about two billion years ago.
Our current arrangement of continents may look set in stone (pun not intended), but what we’re seeing and walking over are the fragments of the ancient supercontinent Pangaea, still drifting apart in a slow motion breakup that’s been going on for over 200 million years.
This is just the latest stage in a cycle where supercontinents form, break apart into smaller continents and other pieces, then drift around until they collide into large landmasses again. This cycle has been estimated to repeat every 600 million years or so, for several billion years.
But how long has this cycle really been happening? This question was the focus of the new study by researchers at Curtin University in Western Australia.
“Our research was essentially testing two hypotheses – one is that the supercontinent cycle started prior to two billion years ago,” says Dr. Yebo Liu, lead author of the study. “Alternatively, the ancient continents (called cratons) only managed to get together in multiple clusters called supercratons, instead of forming a singular supercontinent.”
To find out, the researchers studied rocks that make up the Yilgarn craton, a large ancient landmass that underlies much of Western Australia. It dates back to between 2.9 and 2.6 billion years ago, and by studying the magnetic alignment of grains in certain rocks from the area, the researchers are able to reconstruct where these rocks were located, relative to the magnetic North Pole, when they first formed. This technique is known as paleomagnetism.
The team then compared these measurements with data from other cratons around the world. Their analysis seems to suggest that the supercontinent cycle as we know it began around two billion years ago.
“It was clear that we can almost rule out the existence of a long-lived single supercontinent before two billion years ago, although transient supercontinents may have existed” says Professor Zheng-Xiang Li, co-author of the study. “More likely, there could have been two long-lived clusters of cratons, or supercratons, before (two billion years ago) that were geographically isolated from each other, never forming a singular supercontinent.”
Of course, it’s difficult to be conclusive about the Earth’s ancient history, and the team says the debate is far from over. Further data will need to be collected and studied to help paint a more complete picture.
The research was published in the journal Geology.
Source: Curtin University
