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Yahoo
13-04-2025
- Science
- Yahoo
Earth's crust is surprisingly similar to how it was 4 billion years ago
When you buy through links on our articles, Future and its syndication partners may earn a commission. Earth's crust today has a surprisingly similar composition to the planet's first outer shell, or "protocrust," new research finds. This early rocky shell featured chemical signatures previously thought to occur only in continental crusts made by the process of subduction, in which one tectonic plate slides under another. But plate tectonics isn't actually required to produce these signatures, according to the new study published April 2 in the journal Nature. These findings are important for the debate over when our planet's plate tectonics began. No one knows exactly when or why the Earth's surface broke into pancake-like slabs that grind and crash against one another, forming mountains and volcanoes and triggering earthquakes. Related: Earth's crust is peeling away under California Historically, the fact that chemical signatures seen in modern plate tectonic processes occurred in protocrust from Earth's first billion years, during the Hadean eon, had been used as evidence to support the theory that plate tectonics started nearly as soon as Earth had solid ground — roughly 4 billion years ago. "That's probably a flawed argument now," study lead author Craig O'Neill, a geophysicist at Queensland University of Technology in Australia, told Live Science. "Yes, that signature forms today [through plate tectonics]," O'Neill said. "But the assumption that the Earth has always behaved as it does now, all through time, so you can extrapolate that back — that's obviously a bit fraught." The precise signatures under debate are trace elements, such as titanium and niobium, which combine in the crystal structure of rocks as they solidify from hot magma. However, the behavior of these elements depends heavily on the conditions around them. What O'Neill and his colleagues realized was that the chemistry of the molten, early Earth was quite different from today's. As the Earth solidified from molten rock, the iron-rich portions of that magma sank and concentrated, becoming today's metallic core. This means that the mantle became less rich in iron over time. As such, magma from the mantle found in modern subduction zones, such as the Pacific "Ring of Fire," might not act like the magma found on the early Earth. The researchers modeled the behavior of these trace elements under the conditions of the first few hundred millions of years of Earth, a time when the crust, core and mantle were still differentiating and the developing mantle was still iron-rich. O'Neill explained that the pattern they found looked "remarkably like the subduction zone signature," which means the chemical signatures can't be used as evidence that subduction was happening on early Earth. They can also result directly from the initial transition from a planet with a liquid surface to one with a solid surface. RELATED STORIES —How many tectonic plates does Earth have? —Mesmerizing animation shows 1.8 billion years of tectonic plates moving —Is Earth the only planet with plate tectonics? "Some of the evidence people have been using to argue for early plate tectonics is probably not showing you plate tectonics at all," he said. "It's probably showing you older crust." That doesn't mean plate tectonics wasn't happening at that time, at least on occasion, O'Neill added. There was plenty of debris zipping around the young solar system and Earth was frequently bombarded with impacts, some of which would have been big enough to crack the protocrust and start localized periods of subduction. But the whole planet probably transitioned to the plate tectonic system later, between 3.2 billion and 2.7 billion years ago. There's far more evidence of rocks getting recycled and pushed around during that time period, O'Neill argues. "The interesting debate from here on will be what is the interaction between these two signatures through time," he said. "When does the actual, modern signature become important, and is there a clever way to tell the two apart?"
Yahoo
09-04-2025
- Science
- Yahoo
Earth's First Crust May Have Looked Surprisingly Like The One We Have Today
Geologists have made certain assumptions about how the crust making up our planet's earliest surface formed, but a new study has found that Earth's very first protocrust was surprisingly similar to the shell of solid rock in place today. It may mean a complete rethink of how Earth's coat transitioned from a skin of boiling magma to the shifting armor of tectonic plates we now live on, according to the international team of researchers behind the study. "Scientists have long thought that tectonic plates needed to dive beneath each other to create the chemical fingerprint we see in continents," says geochemist Simon Turner, from Macquarie University in Australia. "Our research shows this fingerprint existed in Earth's very first crust, the protocrust – meaning those theories need to be reconsidered." The chemical fingerprint Turner and his colleagues were looking for was a lack of the element niobium. This is one way of identifying rocks at subduction zones, where one plate slides under another – it's thought that the magma forming these rocks loses niobium as the element gets trapped further down. Find the first evidence of low levels of niobium in the geological record, it was thought, and you find the point when continental plates first appeared and started slamming into each other. However, this hypothesis of a differing early crust composition has been called into question before. Here the researchers took a fresh approach. They used mathematical models to figure out the composition of Earth's earliest covering of hard rock, some 4 to 4.5 billion years ago (the Hadean eon). The modeling showed that niobium would be attracted to Earth's core, with no plate tectonics required. It means continental crust formation may have been a part of the original process of layer formation on Earth, not something that came after. The idea is backed up by the behavior of other siderophile elements in the model – elements attracted to iron, such as the iron in Earth's core as it took shape. "I realized there might be a connection between early core formation, high siderophile element patterns, and the infamous negative niobium anomaly observed in continental crust," says Turner. In the many millennia since, it seems continental crust has retained that original chemical signature, less affected by the heavy bombardment of meteorites that changed the composition of Earth's mantle, and ended around 3.8 billion years ago. All of this needs further investigation, of course, but it's an intriguing alternative take on how Earth first became the planet we recognize today, and how that might apply to other planets. It also answers some of the most baffling questions in geological history. "This discovery completely changes our understanding of Earth's earliest geological processes," says Turner. "It also gives us a new way to think about how continents might form on other rocky planets across the Universe." The research has been published in Nature. Did Dire Wolves Just Come Back From Extinction? Here's The Truth. How Do Dogs Perceive The World? It All Starts With The Nose One Brain Receptor Explains Why 'Virgin' Male Worms Take More Risks
