Something Switched On Inside Earth 2.7 Billion Years Ago—and It Made the Planet We Know

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.’” From rock to ‘life-friendly’ 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. But scientists have long “raged over” whether Earth was always like this or if something had to “switch on” in the past 4.5 billion years, she explained. “The question is hard to settle because plate tectonics are very good at destroying the evidence,” Liebmann wrote. And this occurs very naturally; as plates collide, some old crust sinks back into the mantle. At the same time, the crust pushed upward also starts to erode, and the geological record grows fainter. But “against the odds,” she added, some ancient rocks manage to hold onto chemical fingerprints for billions of years—the reason it was even possible to conduct the new research. Geological sleuthing According to Liebmann, older rock within the crust often becomes an ingredient in new crust, leaving a “lasting chemical trace” in the newly formed rocks. This geological inheritance, so to speak, can survive largely undisturbed for billions of years in minerals like feldspar and sulfide compounds, both of which the team studied. Approximately 70% of the samples came from Australia, whereas the remaining materials originated from different parts of the world. The team ran a statistical analysis to determine the rocks’ ages and chemical compositions. They found a remarkably consistent pattern where the isotopic fingerprint suddenly disappeared from the record after around 2.76 to 2.63 billion years ago. “And despite examining thousands of rocks, we never see it again,” Liebmann explained in the statement. “That tells us something fundamental changed in the way Earth’s crust was being formed and transformed, marking a transition towards the dynamic tectonic system we see today.” Many, many miracles She noted in the column that this signature pointed to a very ancient crust that formed around 4 billion years ago, which, in geological terms, isn’t too long after Earth was formed. And at that time, Earth’s tectonics were probably stagnant, melting and remelting the same material to form the granite-like rocks of Earth’s earliest continents. The team isn’t sure how and why Earth shifted from that to the active, consistent plate tectonics we observe today. But whatever the reason, this transformation continued to shape and reshape early Earth. Again, it’s remarkable how many things had to be “just right” for Earth to have ended up the way it is now.