Geologists studying some of Earth's oldest volcanic rocks have found evidence that water was already influencing the planet's interior and helping drive volcanic activity more than three billion years ago. The international team, led by Adelaide University geochemist Dr. Eric Vandenburg, examined ancient rocks from Western Australia's Pilbara Craton.
Their analysis suggests that water had traveled far beneath the surface before contributing to the formation of magma that fed volcanoes resembling those found around the Pacific "Ring of Fire" today. Published in Nature Communications, the findings indicate that Earth may have been recycling water between its surface and interior much earlier than scientists had realized, even though the young planet operated very differently from the world we know now. Vandenburg, from the School of Physics, Chemistry and Earth Sciences, said the ancient rocks offer an unusual opportunity to investigate conditions on Earth billions of years ago.
"These rocks formed more than three billion years ago, when Earth was a very different place," he said. Today, plate tectonics plays a central role in moving water through the planet. At subduction zones, one tectonic plate sinks beneath another, carrying water from the oceans down toward the mantle.
That water can help generate magma, which rises toward the surface and contributes to the volcanoes that help build continents. "The early Earth was too hot for plates to behave that way, so until now it has been unclear whether surface water could have made that journey more than three billion years ago, and if so, how. "What surprised us was finding evidence that large amounts of water had already made their way deep into the Earth's interior and influenced the formation of volcanic rocks." The researchers suggest that another geological mechanism may have moved water into the mantle before modern plate tectonics became established.
They call the process "dripduction." In this scenario, dense, water-rich portions of Earth's cooler outer crust periodically sagged downward and collapsed into the hotter mantle, transporting water with them. As those sections of crust descended, they released their water into the mantle. That water then helped generate magma, which eventually rose, erupted through volcanoes, and cooled into rocks that have survived for billions of years.
"The Earth wasn't operating exactly as it does now, but it appears some of the key processes were already in place," Dr. When Did Earth Begin Recycling Its Surface? The discovery addresses a major question in geology: how early did materials begin moving between Earth's surface and its deep interior?
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