Network of tectonic plates was in place at least a billion years earlier than thought
June 4, 2020
Geophysicists funded by the National Science Foundation have reported that Earth’s ever-shifting, underground network of tectonic plates was firmly in place more than 4 billion years ago — at least a billion years earlier than scientists thought.
Tectonic plates are large slabs of rock embedded in the Earth’s crust and the next layer down, the upper mantle. The interactions of these plates shape all modern land masses and influence the major features of planetary geology — from earthquakes and volcanoes to the emergence of continents.
“Understanding when plate tectonics started on Earth has long been a difficult problem,” said Jun Korenaga, a geoscientist at Yale University and senior author of the new study, published in Science Advances. “As we go back deeper in time, we have fewer geologic records.”
One promising proxy for determining if tectonic plates were operational is the growth of continents, Korenaga said. That’s because the only way to build up a continent-sized chunk of land is for surrounding surface rock to keep sinking deeply over a long period — a process called subduction, which is possible only through plate tectonics.
In the new study, Korenaga and colleagues found evidence of continental growth starting as early as 4.4 billion years ago. They devised a geochemical simulation of the early Earth based on the element argon — an inert gas that land masses emit into the atmosphere. Argon is too heavy to escape Earth’s gravity, so it remains in the atmosphere like a geochemical ledger.
“Because of the peculiar characteristics of argon, we can deduce what has happened to the solid Earth by studying this atmospheric argon,” Korenaga said. “That makes it an excellent bookkeeper of ancient events.”
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