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Monash University geologists shed new light on Earth’s early history through their discovery that continents were weak and prone to destruction in their infancy.
Their research, which is based on mathematical models, is published today in Nature.
The Earth is our home and over its 4,500,000,000 (4.5 billion) year history it has evolved to form the environment we live in and the resources we depend on.
However, the early history of the Earth, spanning its first 1.5 billion years, remains almost unknown and, consequently, little known.
“This was the time of the formation of the first continents, the emergence of the earth, the development of the primeval atmosphere and the appearance of primordial life – all factors that are the result of the dynamics of the interior of our planet,” said the lead author of ARC Future Fellow Dr Fabio Capitanio of Monash University School of Earth, Atmosphere and Environment.
“By reproducing the conditions of the early Earth in computer-generated numerical models, we show that the release of internal primordial heat, three to four times that of today, caused a large melt in the surface mantle, which was then extruded as magma ( molten rock) on the earth’s surface, “he said.
According to the researchers, the surface mantle left by this process was dehydrated and stiff and formed the keels of the first continents.
“Our results explain that continents remained weak and prone to destruction in their infancy, from ~ 4.5 to ~ 4.0 billion years ago, and then progressively differentiated and became rigid over the next billion years. years to form the core of our modern continents, “said Dr. Capitanio.
“The emergence of these first rigid continents has caused their deterioration and erosion, changing the composition of the atmosphere and supplying nutrients to the ocean that sows the development of life.”
Dr. Capitanio specializes in studying the dynamics of Earth’s tectonics and plate movements to better understand the mechanisms that force individual plates or changes in the entire Earth.
The work adds to the knowledge on the formation of the supercontinent and its fragmentation in today’s continents.
The quantitative model used in the study explains the enigmatic degrees of melting and layered structures observed in most cratons on Earth.
The process shows that continents remain weak and prone to destruction in their infancy, then progressively melt and differentiate to become stable continents.
This explains the transition from the Hadean, which covers the first 500 million years of Earth’s history, in which the crust was completely recycled, to the Archean (four to three billion years ago), when the rigid continental keels they are formed and remain preserved over time.
“The geological record suggests that the very first continents did not survive and were recycled within the planet, but this trend dramatically reversed about four billion years ago when the most enduring piece of continents, cratons, appeared,” said Dr. Capitanio.
Only tiny crystals remain from the Earth’s first continental crust, formed more than 4 billion years ago. The mysterious disappearance of this crust can now be explained. The same process that formed a new crust, replacing the old one, is closely related to how the continents have become stable. By extracting the fusion from within the Earth, rigid rafts form under the new crust in the mantle, protecting it from further destruction. The crust thus formed is still preserved in the heart of today’s continents, the cratons.
Cratons track the earliest years of life on our planet and are currently a very small fraction of the surface.
Australia is home to three cratons, the Yilgarn, the Pilbara and the Gawler.
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