Evidence of 'modern' plate tectonics dating to 2.5 billion years ago found in China
A unique rock formation in China holds clues that tectonic plates subducted, or went underneath other plates, during the Archean eon (4 billion to 2.5 billion years ago), just as they do nowadays, a new study finds.
This 2.5 billion-year-old rock, known as eclogite, is rare, forming when oceanic crust is pushed deep into the mantle (the layer between the crust and the core) at relatively low temperatures. This type of high-pressure, low-temperature rock is "largely confined to subduction zones on the present Earth," study co-lead researchers Timothy Kusky and Lu Wang, Earth scientists at the China University of Geosciences, told Live Science in an email.
The study reveals the oldest known eclogites from an ancient mountain belt found in Earth's oceanic crust, the researchers said. The next-oldest rocks of this kind — 2.1 billion-year-old rocks in the Democratic Republic of the Congo — are about 400 million years younger, the researchers said.
While this isn't the oldest evidence of plate tectonics on record — a 2021 study, for instance, dated plate tectonics to about 3.6 billion years ago — the new finding is a valuable data point showing that tectonic plates subducted underneath each other in Earth's "early" days, geologically speaking at least.
Related: Giant tectonic plate under Indian Ocean is breaking in two
Tectonic plates — the moving slabs that make up Earth's outer crust — are responsible for the cycling of materials and elements from deep inside Earth to its oceans, surfaces and atmosphere. For decades, the research team has worked to understand Earth's early history and evolution, "from the time it formed and cooled from a molten ball of magma in space" to when it solidified, forming a rigid outer crust that evolved to the plate-tectonic system we have today, Kusky and Wang said.
Tectonic plates are crucial for heating the planet. Due to moving tectonic plates, "heat is lost from the interior, much like bread floating and moving on a pot of hot boiling stew below," they said. "Whether the transition to a plate-tectonic Earth happened early, or whether the planet evolved through different stages dominated by different mechanisms of heat loss, is one of the most unresolved and debated questions in Earth sciences today."
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