Tiny crystals unearthed in South Africa contain evidence of a sudden transition in the planet’s surface 3.8 billion years ago. The crystals show movements of the earth’s crust that would mark a precursor to the process known as plate tectonics, becoming the oldest evidence of this phenomenon.
An international group of researchers led by scientist Nadja Drabon, from Harvard University in the United States, has discovered in the Barberton Greenstone mountain range in South Africa, zircon crystals with an age of almost 4,000 million years, which show evidence of a process of movement of the earth’s crust not previously identified: it would be the direct antecedent and the most distant evidence of plate tectonics.
A tectonic plate it is a rigid fragment of the lithosphere (the outer layer of the Earth) that is mobilized on the asthenosphere, a more “plastic” and less rigid portion of the upper mantle of the planet. The entire lithosphere is divided into tectonic plates, some large and some smaller.
Consequently, the tectonics of plates is a process that explains the formation of geological structures produced by deformation of the earth’s crust, depending on the dynamics and movement of tectonic plates. This movement is used, for example, to determine the areas most likely to suffer earthquakes, according to the tectonic plates that act in the subsoil and their possible interaction.
much sooner than thought
Now, in a new study published recently in the journal AGU Advances, scientists say they have found the oldest evidence of such movements. According to an article published in Live Science, the findings contradict current estimates so far: it was thought that the solid rock surface that began to cover the planet during the hadean eonor between 4.6 and 4 billion years ago, began to crack and move much later than indicated by the new research.
Some previous studies estimated that plate tectonics began only 800 million years ago, while other research suggested that this system began at least 2 billion years ago. However, the analysis of 33 zircons, with ages between 4,100 million and 3,300 million years, showed for the scientists in charge of the new study that the first precursor movements of plate tectonics on our planet would have begun approximately 3.8 billion years ago.
Crystals that protect history
The team of specialists compared different isotopes, or variants of chemical elements with different numbers of neutrons, in the old identified zircons and in other zircons discovered in other parts of the planet. In these small crystals, no larger than a grain of sand, they found traces of a sudden transition to a kind of primitive plate tectonics.
The finding would be indicating that at that time and in that place on the planet a simple form of subduction would have begun. Subduction is the sinking of a lithospheric plate under the edge of another plate, thus forming the so-called plate boundaries. The researchers have not yet been able to confirm whether this phenomenon occurred global scalebut in any case there are no older records of this type of movement linked to plate tectonics so far.
Destabilization of Long-Lived Hadean Protocrust and the Onset of Pervasive Hydrous Melting at 3.8 Ga. Nadja Drabon et al. AGU Advances (2022). DOI:https://doi.org/10.1029/2021AV000520