To date, Earth is the only planet known to have continents.
We did not know exactly how the continents were formed and developed. However, because the edges of continents overlap thousands of kilometers apart, we know that Earth’s land mass was concentrated into one large supercontinent.
Since the planet doesn’t look like this anymore, something must have caused this supercontinent to break up. Now, we have new evidence that the impact of a giant meteorite played a significant role in this.
The residue was removed from the mineral zircon crystals. It’s from the Western Australian craton, a piece of Earth’s crust that has remained stable for over a billion years.
Known as the Pilbara Craton, it is the best-preserved “slice” of the planet’s crust. And the zircon crystals it contains contain evidence of an ancient meteorite impact before the continents broke up.
“The study of the oxygen isotope composition of these zircon crystals revealed a process that begins with the melting of rocks near the surface and progresses deeper. This is consistent with the geological effect of a giant meteorite impact. Our study provides the first serious evidence that the processes that eventually formed the continents were initiated by a giant meteorite. It must have been similar to the meteorite responsible for the extinction of the dinosaurs. However, it happened billions of years earlier,” explained geologist Tim Johnson from Curtin University.
Work was carried out on 26 rock samples containing zircon fragments. They date from 3.6 to 2.9 billion years ago. The researchers analyzed oxygen isotopes: specifically, the ratios of oxygen-18 and oxygen-16, which have 10 and 8 neutrons, respectively. These data are used in paleogeology to determine the temperature of formation of the rock in which the isotopes are found.
Based on these ratios, the team was able to distinguish three distinct and fundamental stages in the formation and evolution of the craton.
The first is the formation of large amounts of zircon, corresponding to partial melting of the crust. This partial melting, researchers say, was the result of falling meteorites that heated the planet’s crust on impact. The result of this impact was to form a craton. The second stage would be the period of crustal core recycling and stabilization. This should have been followed by a third period of melting and granite formation.
Eventually this core would develop to become the continents of today, as well as the cratons found on the various continents of the world.
These findings are consistent with previously proposed models for the formation of cratons around the world. However, researchers say this is the most serious evidence for the theory.
The study was published in the journal Nature.