Earth is the only planet known to have continents, though exactly how these various landmasses came to exist remains a mystery.
Among the most exciting theories is the idea that a barrage of giant meteorite impacts during the Earth’s “infancy” led to the formation of continental portions stable cells called cratons, and researchers have now provided the strongest evidence yet for this hypothesis.
“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,” explained study author Dr. Tim Johnson, in a statement.
“Studying the composition of oxygen isotopes in these zircon crystals revealed a ‘top-down’ process that begins with melting of rocks near the surface and progresses deeper, consistent with the geological effect of meteor impacts.” giant meteorites.
Previously, researchers had tentatively discussed the idea that Earth’s cratons might have been forged during the “Late Heavy Bombardment,” when the inner solar system was allegedly pummeled by a disproportionately large number of asteroids.
Based on the age and distribution of craters on the Moon, scientists believe the impact rate slowed down significantly between 3.9 and 3.5 billion years ago.
“That the ages of the oldest continental crust in most cratons also span the period from 3.9 to 3.5 [hace mil millones de años] It raises the question of whether this is a coincidence or whether there is a causal relationship,” the study authors write in the journal Nature.
To investigate, the scientists looked for changes in the density of a particular oxygen isotope called oxygen-18 within the Pilbara Craton. Previous studies on large impact craters have revealed that such events cause significant melting of the shallow mantle, resulting in a decrease in oxygen-18 relative to the lighter isotopes.
Their analysis revealed that the Pilbara Craton formed in three stages, the first of which occurred between 3.6 and 3.4 billion years ago. The zircon crystals found within this layer were isotopically light, indicating that they may have “crystallized after an initial giant impact that ultimately led to the formation of the Pilbara craton.”
According to the authors, the collision that triggered this event would have involved a massive space rock measuring “several tens to hundreds of kilometers in diameter.”
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