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Analysis of ancient mineral samples suggests that plate tectonics may have begun operating on Earth as early as 3.3 billion years ago, potentially rewriting our understanding of the planet’s early geological history. This discovery offers new insights into the conditions necessary for the development of continents and the evolution of Earth’s surface.
Researchers led by Shane Whitehouse at the California Institute of Technology conducted a detailed analysis of dozens of zircon crystals collected from the Jack Hills region of Western Australia. Their findings, published on March 2nd in the Proceedings of the National Academy of Sciences, indicate that the early Earth’s crust formed in a more oxidized environment than previously thought. The research also suggests that subduction – where one tectonic plate slides beneath another – was occurring around 3.3 billion years ago.
Because most of Earth’s early rocks have been recycled through plate tectonics, direct geological records from that period are scarce. Understanding the timing of plate tectonics’ onset and the atmospheric and crustal chemistry of the early Earth requires scientists to glance for alternative geological clues.
Zircon, a silicate mineral formed during the cooling of magma, is remarkably resilient and can preserve information about its chemical environment for billions of years. This makes it a key resource for tracing conditions on the early Earth.
The team analyzed the chemical state of the zircon crystals’ rims using high-resolution X-rays. They discovered that uranium within the crystals existed in a more oxidized state than expected. This oxidation suggests that the magma and surrounding environment at the time of the zircon’s formation were relatively oxidizing, implying a greater abundance of oxygen and water on early Earth than previously assumed.
Researchers also compared the temperature and pressure conditions under which the zircons formed. Zircons dating back approximately 4 billion years show evidence of forming at high temperatures and relatively low pressures. However, zircons from around 3.3 billion years ago formed at lower temperatures under similar pressure conditions.
The research team believes this shift indicates that portions of the Earth’s crust were being driven to greater depths and then rising again. This cyclical movement of crustal material is a hallmark of active plate tectonics.
Not all researchers agree with this interpretation. Simon Turner of Macquarie University and Hugh O’Neill of Monash University noted in the journal Nature that the oxidation signals observed in the zircon rims could be explained by factors other than atmospheric oxygen, such as the behavior of gases within the early magma. They suggest that further analysis and a larger sample size are needed.
This research contributes new data to ongoing efforts to reconstruct the environment of Earth’s first billion years. “We are piecing together fragmentary evidence to reconstruct the story of Earth’s origins,” said Whitehouse. “We hope to analyze hundreds more zircon crystals to more precisely define the conditions on early Earth.”
<참고>
doi.org/10.1038/d41586-026-00628-3
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