A handful of ancient zircon crystal found in South Africa have very old evidence that subduction, a key component of plate tectonics, according to a new study published today at AGU Advances, is an AGU journal of high-impact research, open access and commentary throughout. Earth science and space.
These rare time capsules from Earth’s youth point to a transformation of about 3.8 billion years ago from a long, solid rock mass to the active processes that shape our planet today, giving a new clue to the heated debate over when plate tectonics was introduced. movement.
The crust of the earth and the upper layer of the coat under it are cracked into solid plates that run slowly over the viscous but moving lower layers of the mantle rock. Heat from the center of the Earth drives this slow but steady movement, causing volcanic eruptions, earthquakes, and high altitudes.
Estimates of when this process was revived and modern crust was built from more than four billion years ago to 800 million years ago. Uncertainty arises because the geologic record from Earth’s youth is small, due to the effect of the reconstruction of the plate tectonics itself. There is almost nothing left of Hadean Eon, the first 500 million years on earth.
“Hadean Earth is this great mysterious box,” said NadjaDrabon, a geologist at Harvard University and lead author of a new study.
Short-term capsules
In an exciting step forward in solving this mystery, in 2018 Drabon and his colleagues discovered the chronological sequence of 33 zircon crystals from the rare Barberton Greenstone Belt in South Africa, which was formed at different times during the crisis. 800 million years from 4.15 to 3.3 billion years ago.
Zircon is a common accessory mineral accessory on Earth’s crust, but ancient Hadean Eon representatives, 4 to 4.56 billion years ago, are very rare, found in only 12 places on Earth, and usually with less than three numbers per place.
Hafnium isotopes and trace elements stored in Greenstone Belt cones tell a story about earth conditions while shining. Zircons with 3.8 billion years of age and below appear to be formed on the rock under pressure and melt like modern melting points, indicating that the crust may have begun to move.
“When I say plate tectonics, I am referring directly to the formation of an arc, where one plate goes below the other and you have all that volcano – think of the Andes, for example, and the Ring of Fire,” Drabon explained. an old example of depravity.
“In the 3.8 billion years there is a great deal of variability when the crumbs collapse, we have new building blocks and we see geochemical signatures very similar to what we see in modern plate tectonics,” Drabon said.
In contrast, older zircon preserves evidence of a global “protocrust” cap found in the molten mantle stone that has been stable for 600 million years, the study found.
Signs of a change in the world
New research has found similar changes to conditions such as the modern reduction of zircons from other parts of the world, ranging from about 200 million South African zircons.”We are seeing evidence of significant changes on Earth about 3.8 billion to 3.6 billion years ago and the evolution of plate tectonics is one thing.” Said Drabon.
Although not necessarily the case, the results suggest that change may have begun in the world, says Drabon, who may have started and stopped in scattered areas before settling on the world’s most efficient moving plate engine that we see today.
Plate tectonics shape the earth’s atmosphere and space. The emission of volcanic gases and the production of new silicate rocks, which consume large amounts of carbon dioxide into the atmosphere, provokes temperature fluctuations from greenhouse gases or very small gases.
“Without all the recycling and the formation of new crust, we are probably going back and forth between the hot boiling cold and the cold,” Drabon said. “It’s like a weather thermostat.“Plate tectonics, to date, have been observed only on Earth, and may be necessary for the planet to survive, says Drabon, making the origin of the moving plates interesting in early life research.
“The record we have about the ancient world is limited, but just seeing the same changes in many different places makes it possible for it to be a global change in complex processes,” Drabon said. “Some sort of reorganization was taking place on Earth.”
Source Journal Reference: NadjaDrabon, Benjamin L. Byerly, Gary R. Byerly, Joseph L. Wooden, Michael Wiedenbeck, John W. Valley, Kouki Kitajima, Ann M. Bauer, Donald R. Lowe. Destabilization of Long‐Lived Hadean Protocrust and the Onset of Pervasive Hydrous Melting at 3.8 Ga. AGU Advances, 2022; 3 (2) DOI: 10.1029/2021AV000520
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