Plate tectonics – the drifting of continents – may have got underway at least 3.2 billion years ago and could have played a part in the evolution of life, a study of the magnetism of ancient rocks suggests.
“If plate tectonics happened on the early Earth, that means that these processes were likely playing a part in the evolution of that life,” says Alec Brenner at Harvard University.
The rich life of Earth could not exist without plate tectonics, which helps recycle key elements such as carbon and also maintains a relatively stable temperature. “In part, we have plate tectonics to thank for Earth being habitable,” says Brenner.
Previously, the earliest evidence for plate tectonics was around 2.8 billion years ago. Now Brenner, Roger Fu and colleagues have studied a 3.2-billion-year-old volcanic rock formation in Western Australia called the Honeyeater Basalt. They used a newly developed instrument called a quantum diamond microscope, which let them visualise the magnetic fields of an iron oxide mineral called magnetite.
The team looked at a series of rock samples formed over a period of around 180 million years. The magnetic signal within the magnetite was shaped by the Earth’s magnetic field at the time the mineral formed. Changes in the direction of the magnetism in rocks from different times during this period suggest they moved around 2.5 centimetres a year over the 180 million years.
That’s similar to the speed at which the continents move todays, says Brenner. “The takeaway here is that about 3.2 billion years ago, at least some of the Earth’s crust was moving and moving fast enough to suggest that plate tectonics was driving that motion,” he says.
The team checked that the magnetic signal in the rock samples really is from the time that the rock originally formed instead of from a later event. Fu says he is confident that the signal is indeed pristine.
Brenner says it may be possible that plate tectonics goes even further back. “We’re actively working on rocks from Australia and South Africa that are up to 3.5 billion years old – the hope is that we can probe for the presence or absence of tectonics even further back in time.”
Journal reference: Science Advances, DOI: 10.1126/sciadv.aaz8670
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