Earth surface is covered with rigid plates that move, crash into each other and dive into the planet’s interior. But when did this process begin?
One of Earth’s many peculiarities is that, in contrast to all other planets in the cosmos, its surface is composed of inflexible plates that move, collide, and plunge into the planet’s interior.
However, when did the surface of the Earth split into tectonic plates? When did those plates begin to move? Plate tectonics appears to drive the growth and complexity of life, making it a crucial question.
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The exact date that plate tectonics began to take shape is a mystery to geologists; estimates range from 700 million years ago to before 4 billion years ago when Earth was still a baby.
Robert Stern, a geoscientist at the University of Texas, Dallas, told Live Science that the Neoproterozoic (1 billion to 541 million years ago) is when the earliest clear evidence of current plate tectonics was found. Blueschists, metamorphic rocks that occur at subduction zones, or places where the plates meet and plunge into the planet’s interior, and ophiolites, pieces of oceanic crust thrust onto continents, are abundant in the geological record at that time. These common rocks unmistakably demonstrate that plates were colliding and sliding beneath one another, as subduction is a characteristic of plate tectonics.
However, a lot of geologists believe Stern’s perspective is overly conservative.
Rocks that are suggestive of plate tectonics first appeared on a large scale 700–900 million years ago, according to critics. However, they imply that these rocks might have existed earlier and been destroyed throughout time.
For instance, according to Mark Harrison, a professor emeritus of geoscientist at UCLA, many of the rocks from the Indian subcontinent’s collision with southern Asia only 55 million years ago have already worn away. Harrison stated to Live Science that “the Tibet-India collision isn’t over yet.” What chance is there of discovering these identical rocks from the far more distant past if tectonic evidence is vanishing as a plate-to-plate collision is taking place?
Stern contends that there is proof of a brief subduction episode that occurred 1.8 billion years ago but did not fully take, supporting his theory that the rock record would have made it more obvious if plate tectonics had been regular before roughly 800 million years ago. (This blip is seen by other experts as proof that plate tectonics was far advanced by that time.)
The shift to plate tectonics was predicted by many scientists to occur considerably sooner. The exact time of the geologic shift is estimated to have occurred between 2.5 billion and 3.8 billion years ago, however there are many indications that it occurred during the Archean Eon (4 billion to 2.5 billion years ago). For instance, at least one 2.5 billion-year-old ophiolite has been maintained to this day.
The chemistry of the crust provides more evidence. The chemistry of the crust will resemble the mantle from which it originated if it is composed of recently formed volcanic rock. This chemistry changes if plate tectonics recycles and remelts it. Around 3 billion years ago, more crust started to be recycled, according to a significant 2012 study. According to research co-author Chris Hawkesworth, an emeritus professor of geosciences at the University of St. Andrews in the United Kingdom, this could signal the transition to subduction destroying and reworking crust.
The Earth’s crust may have undergone a shift some 3.8 billion years ago, according to research on zircons, which are minerals that endure even when the rocks surrounding them melt and reform. “We start to see zircon structures that start to look more and more like what we see in subduction zones today, study author Nadja Drabon, an Earth and planetary scientist at Harvard University, told Live Science. Around that time, the crust also became shorter-lived, which further supports the subduction recycling process.
However, does this shift accurately depict plate tectonics? According to 2023 zircon research, which examined the Earth’s magnetic field conditions at the time the minerals originated, these grains essentially remained in place until 3.4 billion years ago, suggesting that landmasses weren’t moving until then.
Drabon pointed out that it’s feasible that distinct features of plate tectonics developed at various points in time. The continents took some time to begin migrating around the world, but subduction may have begun as early as 3.8 billion years ago.
According to a more recent and contentious theory, plate tectonics originated in the Hadean (4.5–4 billion years ago). According to zircon research and the chemistry of the oldest surviving rocks on Earth, there is growing evidence that the early Earth was a remarkably modern environment with continents and oceans. According to some research, the earliest zircons on Earth, which originate from this enigmatic era of geologic history, bear a striking resemblance to zircons that currently form in volcanic arcs above subduction zones. Additionally, according to theoretical modeling, plate tectonics might exist under Hadean conditions, Yale University professor of Earth and Planetary Sciences Jun Korenaga told Live Science.
Each of these origin myths has flaws in every piece of evidence. For example, the Jack Hills in Australia are the source of the great majority of very old zircons, which may not accurately reflect events occurring elsewhere in the world. Perhaps the reason the oldest rocks are still present today is because they were different from all the other rocks on ancient Earth. When computer modelers are debating their presumptions about the condition of the mantle four billion years ago, you don’t want to get involved.