A new study shows that the Archean eon (4 billion to 2.5 billion years ago) was similar to the present day.
This 2.5 billion-year-old rock, known as eclogite, is rare, forming when the ocean's crust is pushed deep into the mantle. Timothy Kusky and Lu Wang, Earth scientists at the China University of Geosciences, told Live Science in an email that this type of rock is confined to subduction zones on the present Earth.
The oldest known eclogites from an ancient mountain belt were found in the ocean. The Democratic Republic of the Congo's 2.1 billion-year-old rocks are 400 million years younger than the next-oldest rocks of this kind.
This isn't the oldest evidence of plate tectonics on record, but the new finding is a valuable data point showing that the plates subducted underneath.
There is a giant tectonic plate under the Indian Ocean.
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.
The plates are important for heating the planet. They said that heat is lost from the interior due to the plates moving.
For the past 20 years, the research team has mapped Archean eon rocks in northern China, which is an orogen, a mountain belt.
The features in the rocks indicate that the mountain belt was formed as a result of the interaction between the plates. The ancient collision zone contains fragments of the oceanic crust, as well as a mixture of rocks that mark the spots where the plates collided, according to the researchers. The team found large folded structures, called nappes, that were pushed from hundreds to thousands of miles away.
The discovery of the eclogites within the mE9;lange reveal that a tectonic slab of oceanic crust subducted under another plate, metamorphosing, that is, having its composition, texture or internal structure altered by heat and pressure.
It is rare to find eclogites from the Archean eon, which has led to an assertion that modern plate tectonics did not operate in the Archean.
The eclogites were transported across the ocean floor and pushed into the mantle after forming at a spreading ridge about 2.5 billion years ago. Microstructures in the minerals were found to have temperatures between 1,458 and 1,634 degrees Fahrenheit and high pressures between 287,000 and 355,000 pounds per square inch.
The figures suggest that the eclogites were at least 40 miles deep. Kusky and Wang said that these findings are similar to data from minerals found at modern subduction zones.
Scientists created a map of the show.
The pressure from the two colliding plates squeezed the dense rocks back up to the surface, like a watermelon seed between your wet fingers, according to Kusky and Wang.
Nicolas Greber, a professor at the Institute of Geological Sciences at the University of Bern who was not involved in the research, told Live Science that it was an interesting study.
Roberta Rudnick, a professor of Earth science at the University of California, Santa Barbara who was not involved in the study, said that the findings were unsurprising.
Rudnick said that the whole topic of when plate tectonics start is not settled. I think most of the community would approve of plate tectonics being in operation by 2.5 billion years ago.
The study was published in the journal on April 4.
It was originally published on Live Science.
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