How did Earth’s tectonic plates form? You might think that this would be an easy question to answer, considering that we are now trying to pin down the details of when it happened, and if there is tectonic activity on the Moon. But our knowledge of how this planetary mechanism arose is surprisingly scarce.
Researchers from China, Hong Kong, and the United States have now come up with a new hypothesis, one that, at face value, looks incredibly similar to an idea discredited decades ago, but now deserves to be revised.
Tectonic plates have been shuffling around the surface of our planet from 3.3 billion to 4.4 billion years ago, depending on who you ask. But a few billion years of tectonic movement and recycling of the crust have meant that it is quite difficult to determine how the Earth came to have tectonic plates in the first place.
A couple of years ago, researchers developed a model showing that tectonic plates first formed in a process similar to how they continued to move, with some parts of the Earth’s crust dipping below each other and starting a chain reaction of pieces. bark. that lasted millennia.
But the new research presents a model that shows something quite different. The research team proposes that billions of years ago, Earth’s newly formed shell warmed up, causing an expansion of the shell, leading to a fracture resulting in what we now know as tectonic plates.
“Here we use 3D spherical shell models,” the team writes in their new paper, “to demonstrate a self-organizing fracture mechanism analogous to lithospheric elevation driven by thermal expansion.”
(Tang et al., Nature Communications, 2020)
Above: A snapshot of the model showing the latest stages of growth and coalescence on Earth’s tectonic plate. The fractures are in black and the colors show stresses.
Now, the expanding Earth hypothesis is not a new idea. In the 19th century, an expanding Earth was proposed to explain how geographic features such as mountains were formed; However, it was discredited when we discovered plate tectonics.
But the new scenario is not the same as the one presented during the Charles Darwin era. The crucial difference comes down to where the Earth let off steam so many years ago.
“The answer lies in the consideration of the main heat loss mechanisms that could have occurred during the early periods of Earth,” said University of Hong Kong planetary scientist Alexander Webb.
“If volcanic advection, which carried hot material from deep to the surface, was the primary mode of early heat loss, that changes everything.”
It boils down to whether Earth’s heat loss occurred by conduction (radiating equally across the planet) over a long period of time, or whether volcanoes spewed lava (and heat) from the planet’s interior to the surface where He cooled.
This accumulation of cooled material would eventually have sunk and cooled the lithosphere, slowing down the volcanoes along with the general cooling of Earth. In turn, this would have trapped the planet’s internal heat, which expanded the crust, causing it to crack and form tectonic plates.
“Our numerical experiments show that polygonal fissures could develop on Earth’s surface in response to shallow lithospheric processes, with triple junctions as by-products of fracture,” the team writes in their article.
“The rapid development of the fracture network in each experiment occurs at a total expansion of about 1 km and takes ~ 5 million years.”
It is important to note that this study is only a hypothesis. We are still a long way from understanding what happened on ancient Earth to result in tectonic plates. But with more evidence, this hypothesis could be an important part of solving the unique characteristics of our planet.
The research has been published in Nature’s Communications.
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