So far, we know of only one planet with continents: Earth. The exact way they formed and evolved remains a mystery, but we know -- from the fact that continents' edges seem to line up -- that the landmass of the planet was once concentrated on one big supercontinent.
Based on current knowledge of the solar system and how it formed, scientists believe our planet formed about 4.54 billion years ago by accreting dust and gas from the solar nebula.
A combination of extreme volcanism and collisions with other bodies initially caused the Earth to become molten. A solid crust formed when water accumulated in the atmosphere and cooled the outer layer of the planet. Moon formation is thought to have resulted from the impact of a planetoid on Earth soon afterward.
In the course of hundreds of millions of years, the surface of the earth reshaped itself continuously. Sometimes, continents joined to form supercontinents as they migrated across the surface.
A supercontinent called Rodinia began to break apart roughly 750 million years ago. Pannotia was formed 600 to 540 million years ago, followed by Pangaea, which broke apart 200 million years ago.
But how did the continents form? They were not always there, or were they?
A new study from Curtin University provides the strongest evidence yet that Earth’s continents were formed by giant meteorite impacts.
Our planet experienced more of these events in the first billion years of its 4.5 billion-year history, the researchers reported in Nature.
The idea that continents formed from giant meteorite impacts has been around for decades, but there has been little hard evidence to support it until now, according to Dr. Tim Johnson at Curtin School of Earth and Planetary Sciences.
Researchers found evidence of these giant meteorite impacts by studying zircon crystals in rocks from Western Australia’s Pilbara Craton, one of the best-preserved remnants of the Earth’s ancient crust.
In these zircon crystals, the oxygen isotope composition revealed a “top-down” process that began with melting rocks near the surface and progressed deeper, corresponding with the geological effects of giant meteorites.
“Scientists have demonstrated for the first time that the processes that led to the formation of continents were initiated by giant meteorite impacts similar to those responsible for the extinction of dinosaurs billions of years earlier,” says Johnson.
In this sense, he emphasizes the importance of understanding the formation and evolution of Earth’s continents since they contain most of Earth’s biomass, humans, and mineral deposits.
Besides lithium, tin, and nickel, the continents also harbor a wide range of other essential metals that can be used to develop environmentally friendly technologies.
“These mineral deposits are the end result of a process known as crustal differentiation, which began with the formation of the first landmasses, of which the Pilbara Craton is just one of many,” Dr. Johnson explained.
Other ancient areas of the Earth’s continental crust appear to show patterns similar to Western Australia’s. Scientists want to test their findings in these ancient rocks to determine if the model is more broadly applicable.
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