A recent paper by David Hernandez Uribe of the University of Illinois Chicago, published in *Nature Geoscience*, brings new data into the debate, challenging the dominant theory of continent formation. Using computer models, Hernandez Uribe examined the formation of magmas believed to be crucial to understanding the origin of continents.
Magma, the molten material that cools to form rocks and minerals, was the focus of Hernandez Uribe's study. He sought magmas with compositional signatures matching rare mineral deposits known as zircons, which date back to the Archaean period, 2.5 to 4 billion years ago, when it is believed that continents first formed.
In the previous year, researchers from China and Australia published a study suggesting that Archaean zircons could only form through subduction - a process where two tectonic plates collide underwater, pushing land masses to the surface. This process, which causes earthquakes and volcanic eruptions, continues to shape continental coasts today.
However, Hernandez Uribe, an assistant professor of earth and environmental sciences, discovered that subduction was not essential for the formation of Archaean zircons. His findings indicated that the minerals could form under high pressure and temperatures from the melting of the Earth's thick primordial crust.
"Using my calculations and models, you can get the same signatures for zircons and even provide a better match through the partial melting of the bottom of the crust," Hernandez Uribe said. "So based on these results, we still do not have enough evidence to say which process formed the continents."
These findings also cast doubt on the timeline for the start of plate tectonics on Earth. If the first continents formed by subduction, then tectonic activity could have started as early as 3.6 to 4 billion years ago, within 500 million years of Earth's formation. Conversely, the alternative theory suggests that if continents formed from melting crust, subduction and tectonic activity might have started much later.
"Our planet is the only planet in the solar system that has active plate tectonics as we know it," Hernandez Uribe said. "And this relates to the origin of life, because how the first continents moved controlled the weather, it controlled the chemistry of the oceans, and all that is related to life."
Research Report:Archaean oxidizing and wet magmas from mafic crustal overthickening
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