In many ways, life on Earth feels like a miracle. Had things gone differently, Earth might have looked more like our neighbors in the solar system. Scientists long suspected that plate tectonics was partly responsible for how Earth evolved, but pinning down when it began has proven difficult.

Now, researchers have identified a “chemical fingerprint” that points to when plate tectonics likely began. The team studied over 1,200 rocks spanning nearly 4 billion years of Earth’s history, publishing their findings in Proceedings of the Royal Society A.

This fingerprint—specifically, an isotopic signature of lead—appears consistently in rocks older than 2.76 to 2.63 billion years but abruptly disappears in younger rocks. This suggests something “switched on” around 2.7 billion years ago, and our planet experienced major shifts in the way it forms continents. The team isn’t sure yet what that “something” is, but this tectonic turning point likely played an integral role in how Earth grew to be the planet we know today.

“Plate tectonics is fundamental to the way Earth has evolved over billions of years, continually reshaping the continents and oceans and influencing the planet’s atmosphere and climate,” Chris Kirkland, a study co-author and a geoscientist at Curtin University in Australia, said in a statement. “This gives us our clearest geological evidence yet for when the tectonic engine that drives the modern Earth ‘switched on.’”

In a column for The Conversation, study lead author Janne Liebmann shared further details on the latest work. According to Liebmann, a research fellow at Curtin University, plate tectonics play a huge role in regulating Earth’s climate and magnetic fields, in addition to forming mountains and oceans and triggering earthquakes.

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