About 3 billion years ago, Earth‘‘s crust bubbled during a massive growth storm, geoscientists have found.
At that time, just 1.5 billion years after the Earth formed, the mantle – the layer of silicate rock between the crust and the outer core that had been more active in the past – heated, causing magma to break out of the layer into fragments. from older crust outflow. up there. These fragments had a ‘seed’ for the growth of today’s time continents.
The researchers found evidence for this growth sprout hiding in ancient zircon crystals in stream deposits in Greenland. These extremely durable crystals – consist of zirconium silicate – formed during the growth storm about 3 billion years ago.
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“There have probably been several crustal events in Earth’s history,” lead researcher Chris Kirkland, a professor of geoscience at Curtin University in Australia, told WordsSideKick. “But this global injection event 3 billion years ago is definitely one of the biggest.”
Continental seeds
Before this massive growth period, the ancient crust of the earth was much thinner and weaker than it is today. Eventually it breaks out into crust fragments that serve as floating “life rafts” from which new crust can grow.
“We think of crust as this living material that sits on top of the mantle,” Kirkland said. “This means that it is constantly getting an injection of new material coming from below. The longer it sits on top, the more new material is injected into it and the bigger it gets.”
Mantle temperatures peaked at the time due to the radioactive decay of elements such as uranium and potassium in the core of the earth, as well as residual heat, left the planet’s formation. As the global peak in temperatures spurred the process, the crust, according to the researchers, continued to balloon on a massive scale for a period of about 200 million years.
At the end of this period, the first continents began to take shape, which eventually made possible the development of complex life on land about 400 million years ago.
Analysis of crystals
The evidence for this growth storm was that there was ingrowth of zircon crystals of less than 100 microns in size (less than the width of a human hair) eroded from rocks and stored in stream deposits in West Greenland.
“Zircon is like the geologist’s favorite toolkit because it can tell us so much,” Kirkland said. “The crystal is very robust, it holds information about its origin.”
Like trees, the crystals have growth rings caused by periods of magma injection. To accurately age these rings, Kirkland and his colleagues blew the crystals with an ion beam – a beam of charged particles that could accurately break the super-strong miniature crystals – to separate the ring segments for individual analysis.
By dating the isotopes – versions of elements with a different number of neutrons in each atom – within each ‘ring’ they found that the crystals consist of old (4 million years old) and newer (3 million years old) crust. This supports their hypothesis that older crust fragments serve as seeds for the formation of newer crust.
“It’s pretty amazing that you can sum up the ancient history of our planet from these individual grains,” Kirkland said. “It’s like being able to tell the age of someone’s parents just by looking at them.”
Other studies conducted by various researchers in Australia, South Africa and Scotland – all places where you can find exposed ancient rocks – have found similar results, proving that it was also part of a major global injection event.
Understand the earth’s crust
In addition to the “wow” factor of discovering how the outer shell of the earth formed so long ago, the results can also be used to locate new sources of depleted metals for mining.
“Western Australia is a good example,” Kirkland said. ‘We have quite a lot gold, iron and nickel reserves, but most of these occur in shallow crusts. When we start using up these resources, we need to look for new ones in the deeper crust. ‘
However, he conceded that it would be more difficult to access these new resources and to exploit them would be a major logistical challenge. Instead, he thinks the real value in discovering his team is academic.
“It’s about understanding how these formative little pieces of crust evolved,” Kirkland said. “Compiling things that happened billions of years ago from these little grains is incredible.”
The study was published in the journal on January 12. Nature communication.
Originally published on Live Science.