A new study suggests that Earth’s first crust formed continents and plate tectonics earlier than previously thought, with potential ramifications for theories about when life on the blue planet first evolved.
Rock on a shelf with name tag
Modern continental rock. Credit: Morris McLennan, Macquarie University (CC BY-NC-ND)
The research is published in Nature.
“This discovery has major implications for how we think about Earth’s earliest history,” says study lead Simon Turner, a professor at Australia’s Macquarie University.
“Scientists have long thought that tectonic plates needed to dive beneath each other to create the chemical fingerprint we see in continents,” Turner adds. “Our research shows this fingerprint existed in Earth’s very first crust, the protocrust – meaning those theories need to be reconsidered.”
Some researchers believe that the development of plate tectonics is the hidden secret to the origin of life on Earth.
Identifying when plate tectonics first began could then give insight into when life began.
Subduction zones – where one plate has slipped beneath the other – have a distinctive chemical signature marked by low levels of the element niobium. So, geologists have long assumed that finding the oldest low-niobium rocks would be indicate the beginning of plate tectonics.
But the results of such research have been inconsistent.
“I began to wonder if we were asking the right question,” says Turner.
His team created mathematical models simulating conditions on Earth soon after it formed 4.54 billion years ago. The models show that the protocrust, which formed between 4.5 and 4.0 billion years ago, would have had the same chemical signature found in today’s continents without needing plate tectonics.
“This early crust was reshaped and made richer in silica thanks to a combination of meteor impacts, chunks of crust peeling off, and the beginning of plate movements,” Turner explains.
The report says Earth’s first crust likely broke into pieces that became thicker in places. This would have been the beginnings of the continents. As the pieces moved across the planet’s surface, the molten magma between them created crust similar to what is found on the ocean floor today.
“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.”
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