The ways in which, between 4 and 2.5 billion years agoon the surface of our planet were formed the first continents are often the subject of debate among scientists. A new study, conducted by David Hernandez Uribea professor at the University of Illinois Chicago, questions the most widely accepted theory that the first continents were formed by emergence from the ocean of continental masses, due to the sinking (subduction) of the lithospheric plates one under the other. Researchers had recently found evidence of the phenomenon, but thanks to the analysis of ancient magmas Hernández Uribe would have refuted them, thus also casting doubt on the beginning of the plate tectonicsDating the beginning of tectonics is crucial because the movement of the continents has influenced theorigin of life on Earth.
Previous studies on the formation of the first continents and subduction
When it originated, 4.6 billion years agothe Earth was completely molten. Its surface began to solidify forming a crust only when the planet cooled down. From this crust then originated the first continentsvery different from the current ones. To study their formation, in recent years researchers have examined rare minerals originating from the solidification of magma, called zirconiadating back to the eon Archean (time interval extending between 4 and 2.5 billion years ago). The results of the studies suggested that these minerals could have formed only following the process known as subduction. This is the phenomenon, still in progress today, by which a plate of lithosphere sinks beneath the adjacent one on the ocean floor and because of which continents form, change and move over time. In the Archean, the subduction process would have brought portions of crust to depth, which would have thus reached the temperature and pressure values necessary for the formation of Archean zircons.
The results of the new study on the origin of the continents
Hernández Uribe used computer models to study the formation of particular magmas that could provide clues to the origin of the first continents. The magmas have revealed that the formation of Archean zircons does not require the process of subduction. These minerals could have originated instead from the partial fusion of the lower part of the primordial crust (in the presence of high pressures and temperatures) and its subsequent solidification.
These results show how necessary it is further research to establish what process gave rise to the first continents.
The implications in plate tectonics
Hernández Uribe’s studies could also call into question thebeginning of plate tectonics (of which subduction is a characteristic process). If the first continents formed following subduction, it means that plate tectonics could have started already 4 billion years agojust 600 million years after the Earth’s origin. According to the new study, which finds that subduction was not necessary for zircon formation, tectonics may have instead begun later. Dating the beginning of plate tectonics is crucial because it is the basis of the movements of the continents. In turn, the birth and movement of the continents have conditioned the climate of the Earth, the chemistry of the oceans and consequently the origin of the life on earthof which the first evidence dates back to around 3.5 billion years ago.
