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About 3 billion years ago, Earth‘The crust swelled during a massive growth spurt, geoscientists found.
At that time, just 1.5 billion years after Earth was formed, the mantle – the layer of silicate rock between the crust and the outer core that was more active in the past – warmed, causing ooze magma from this layer in fragments of older crust. Above. These fragments acted as “seeds” for modern day growth continents.
Researchers have found evidence for this growth spurt hidden in ancient zircon crystals in the sediment Greenland. These extremely durable crystals – made up of zirconium silicate – formed during the growth spurt about 3 billion years ago.
Related: Photo timeline: how the Earth formed
“There have likely been several scab-forming events in Earth’s history,” lead researcher Chris Kirkland, professor of geosciences at Curtin University in Australia, told Live Science. “But this global injection event 3 billion years ago is certainly one of the most important.”
Continental seeds
Before this period of massive growth, the ancient earth’s crust was much thinner and weaker than it is today. Eventually, it shattered into crustal fragments that served as floating “life rafts” from which new crust could develop.
“We think of the crust as that floating material that sits on top of the mantle,” Kirkland said. “That means he’s constantly getting an injection of new material from below. The longer it stays on top, the more new material is injected into it and the more it grows.
Mantle temperatures peaked at the time, due to the radioactive decay of elements like uranium and potassium in the core of the Earth, as well as waste heat left the formation of the planet. Since this spike in global temperatures spurred the process, the crust continued to swell on a massive scale for a period of around 200 million years, the researchers said.
At the end of this period, the first continents began to take shape, eventually allowing the development of complex life on earth around 400 million years ago.
Crystal analysis
Evidence of this growth spurt appeared rooted zircon crystals, less than 100 microns in size (less than the width of a human hair), which had been eroded by rocks and accumulated in yard sediments. of water in West Greenland.
“Zircon is like a geologist’s favorite toolbox because it can tell us a lot,” Kirkland said. “The crystal is very robust, it imprisons information about its origins within itself.
Like trees, crystals have growth rings, caused by periods of magma injection. To precisely age these rings, Kirkland and his colleagues blasted the crystals with an ion beam – a beam of charged particles capable of precisely fracturing super powerful miniature crystals – to separate the ring segments for individual analysis.
Dating isotopes – versions of elements with different numbers of neutrons in each atom – inside each “ring”, they discovered that the crystals consisted of an old (4 million years old) and more recent (3 million years old) crust. This supported their hypothesis that the fragments of the older crust acted as seeds for the formation of a new crust.
“It’s pretty amazing that from these individual grains you can piece together the ancient history of our planet,” Kirkland said. “It’s a bit like being able to tell the age of someone’s parents just by looking at them.”
Other studies by different researchers in Australia, South Africa and Scotland – all places where you can find ancient rocks exposed – found similar results, proving that this was also part of an event of massive global injection.
Understanding the Earth’s Crust
In addition to the “wow” factor of finding out how the Earth’s outer shell formed so long ago, the findings could also be used to help locate new sources of depleted metals for mining.
“Western Australia is a good example,” Kirkland said. “We have quite a few gold, the iron and nickel reserves, but most are found in shallow crusts. As we begin to use these resources, we must seek new ones in the deeper crust. “
However, he admitted that these new resources would be more difficult to access and that their exploitation would be a huge logistical challenge. Instead, he believes the real value of his team’s discovery is academic.
“It’s about understanding how these little pieces of crust that we live on developed,” Kirkland said. “To be able to piece together things that happened billions of years ago from these tiny grains is amazing.”
The study was published on January 12 in the journal Nature communications.
Originally posted on Live Science.
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