New research has uncovered the strongest evidence yet that Earth’s continents were formed by giant meteorite impacts, which were especially common during the first billion years or so of our planet’s four-and-a-half-billion-year history. Curtin University researchers conducted the study, which was published on August 10, 2022, in the journal Nature.
According to Dr. Tim Johnson, from Curtin’s School of Earth and Planetary Sciences, the idea that the continents originally formed at sites of giant meteorite impacts has been around for decades. However, until now there was little solid evidence to support the theory.
“By examining tiny crystals of the mineral zircon in rocks from the Pilbara Craton in Western Australia, which represents Earth’s best-preserved remnant of ancient crust, we found evidence of these giant meteorite impacts,” Dr. Johnson said.
“Studying the composition of oxygen isotopes in these zircon crystals revealed a ‘top-down’ process starting with the melting of rocks near the surface and progressing deeper, consistent with the geological effect of giant meteorite impacts.
“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 which occurred billions of years earlier.”
Understanding the formation and ongoing evolution of the Earth’s continents is crucial according to Dr. Johnson because these landmasses host the majority of Earth’s biomass, all humans, and almost all of the planet’s important mineral deposits.
“Not least, the continents host critical metals such as lithium, tin, and nickel, commodities that are essential to the emerging green technologies needed to fulfill our obligation to mitigate climate change,” Dr. Johnson said.
“These mineral deposits are the end result of a process known as crustal differentiation, which began with the formation of the earliest landmasses, of which the Pilbara Craton is just one of many.
“Data related to other areas of ancient continental crust on Earth appears 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 widely applicable.”
Reference: “Giant impacts and the origin and evolution of continents” by Tim E Johnson, Christopher L Kirkland, Yongjun Lu, R Hugh Smithies, Michael Brown and Michael IH Hartnady, 10 August 2022, Nature.
dr Johnson is affiliated with The Institute for Geoscience Research (TIGeR), Curtin’s flagship earth sciences research institute.