A new study by researchers at Curtin University in Perth, Australia, has found that Earth’s continents were formed when our planet was bombarded by giant meteorites some 3.5 billion years ago.
Large meteorite collisions appear to have been particularly frequent during the first billion years or so of our planet’s history (the 4,543 billion years since its formation). Over the course of Earth’s 4.5 billion year history, land masses have fragmented, split apart, and come back together. This is the result of heat from radioactive processes within the planet’s interior causing these plates to move.
Until now there was little hard evidence to support the theory.
The experts analyzed crystals of the mineral zircon from the Pilbara craton in Western Australia, a region known for its ancient landscapes; an old and stable area of the earth’s crust, to investigate its origins. (A craton is a piece of the planet’s crust that has remained intact for billions of years.)
“By examining tiny crystals of the mineral zircon in rocks from the Pilbara Craton in Western Australia, which represents the best-preserved remnant of Earth’s ancient crust, we found evidence of these giant meteorite impacts,” said Tim Johnson of the School of Planetary Sciences. and Curtin’s Land.
“Studying the composition of oxygen isotopes in these zircon crystals revealed a ‘top-down’ process that begins with the melting of rocks near the surface and progresses deeper, consistent with the geological effect of Earth impacts.” giant meteorites.
The three types of oxygen isotopes, different forms of the element, found within zircon indicate that the craton formed in three stages. The study of the crystals showed that the heat that melted and transformed the rock did not come from below, but from above. This would be more consistent with a giant meteorite impact than, say, with the Earth’s molten core.
“Our research provides the first solid evidence that the processes that ultimately formed the continents began with giant meteorite impacts, similar to those responsible for the extinction of the dinosaurs, but that occurred billions of years earlier.”
The first stage was a giant shock about 3.6 billion years ago that destroyed part of the planet’s crust and, as a result, reduced the pressure on the lower mantle.
“Data relating to other areas of ancient continental crust on Earth appear to show patterns similar to those recognized in Western Australia. We would like to test our findings on these ancient rocks to see if, as we suspect, our model is more applicable ,” they conclude. the authors in their study published in the journal Nature.
This finding undermines a contrary theory that cratons formed as a result of ancient volcanic activity.
In future work, the team would like to see if the findings from this Pilbara craton study are applicable to other areas of ancient continental crust.
Referencia: Tim E. Johnson, Christopher L. Kirkland, Yongjun Lu, R. Hugh Smithies, Michael Brown, Michael I. H. Hartnady. Giant impacts and the origin and evolution of continents. Nature, 2022; 608 (7922): 330 DOI: 10.1038/s41586-022-04956-y