Scientists estimate that the first plate tectonic happened between 4 billion to 800 million years ago. However, a team from Harvard University confirmed that it happened 3.8 billion years ago based on their study of ancient zircon crystals they found in South Africa.
EarthSky.org reported that these crystals served as time capsules and the earliest known evidence of subduction, the geological process by which a plate tectonic dives under another.
Crystals Serve As Time Capsules For the First Plate Tectonics 3.8 Billion Years Ago
The First Plate Tectonics
Plate tectonics is a geological process by which the crust and top layer of the mantle are broken into separate massive and rigid plates that slowly move atop a viscous or sticky layer of the mantle. The heat from the Earth's core fuels the movement and other geological events, such as earthquakes, volcanic eruptions, and mountain formations.
Before the transition of plate tectonics, Earth's crust was rigid and immobile. But with the takeover of this process, the Earth's crust has become dynamic and active. Scientists hypothesize that it also contributed to the habitability of Earth because it assisted in the evolution of simple microorganisms to more complex lifeforms and even helped make the planet remain habitable.
In their study, titled "Destabilization of Long-Lived Hadean Protocrust and the Onset of Pervasive Hydrous Melting at 3.8 Ga" published in AGU Advances, researchers reported that the transition period began 3.8 million years ago.
Until now, scientists had a hard time determining when plate tectonics first happened because the plates are flowing under each other which has erased much of their geological record during the Hadean eon 500 million years ago.
Clues to Plate Tectonics History Found in Zircon Crystals
In 2018, study lead author Nadja Drabon, a professor of Earth and planetary sciences at Harvard University, and colleagues discovered 33 zircon crystals in the Green Sandstone Bed in South Africa. According to Live Science, these crystals range between 4.1 billion and 3.3 billion years old.
The team analyzed different isotopes found in those ancient zircon crystals and other zircons from other times and places on Earth. Scientists found evidence of a sudden transition to primitive plate tectonics that dates 3.8 billion years ago, which suggests simple subduction occurs in at least one place on Earth.
Furthermore, isotope analysis of oxygen, niobium, and uranium showed that the rocks from the surface held water as early as 3.8 billion years ago. That means those zircon crystals were buried on an ancient seafloor. Drabon told Live Science that extrapolating from the earliest samples from 4.1 billion years ago means that the planet had a solid crust 4.2 billion years ago.
Therefore, Earth's magma sea persisted only until the late Hadean eon, contrary to the previous belief that Earth was just covered by magma ocean until 3.6 billion years ago.
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