With tectonic plates bumping and grinding against each other, Earth is a pretty active planet. But when did this activity begin? A new study from Yale University claims to have found evidence that plate tectonics started about a billion years earlier than is currently thought, which places it very soon after the planet’s formation.
The Earth’s crust is made up of solid rock gliding along on top of the more fluid mantle. But it’s not one solid piece – the crust is split up into tectonic plates, which gradually move around the surface. This process creates deep ocean trenches, gigantic mountain ranges and the continents themselves, as well as events like earthquakes and volcanic eruptions.
Based on a range of geological evidence, it’s generally thought that plate tectonics began between 3 and 3.5 billion years ago. But there’s a clear problem there: by nature the moving plates could be erasing the older evidence of their existence.
“Understanding when plate tectonics started on Earth has long been a fundamentally difficult problem,” says Jun Korenaga, senior author of the study. “As we go back deeper in time, we have fewer geological records.”
So for the new study, the Yale team looked to a different source – one that won’t be wiped clean by the very thing they’re trying to study. And that source is the amount of argon in the air.
Argon is an inert gas and the third-most abundant gas in the atmosphere today. The vast majority of it was put there from radioactive decay in the Earth’s crust. And since argon is such a heavy gas, it doesn’t escape into space. That means it just sits there and accumulates over time, giving scientists an indication of how long the crust has been emitting it.
“Because of the peculiar characteristics of argon, we can deduce what has happened to the solid Earth by studying this atmospheric argon,” says Korenaga. “This makes it an excellent bookkeeper of ancient events.”
The researchers created a geochemical simulation of early Earth, based around argon. While also accounting for argon produced through other means, the team found evidence of continental growth dating from as early as 4.4 billion years ago. The team says this is a good proxy for plate tectonics, since continents can only really be built up through subduction, when one plate sinks under another. That would mean plate tectonics arose just 100 million years after the formation of Earth itself.
Intriguing as the new study is, the case is far from closed. Another recent study reached essentially the opposite conclusion, proposing plate tectonics started much more recently than expected, just 600 million years ago. This was signaled by the cataclysmic “Snowball Earth” event.
The new study was published in the journal Science Advances.
Source: Yale University
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