Geologists Found Remnants Of Earth’s Mantle That Have Lasted Over 2.5 Billion Years And Challenge Previous Beliefs About Our Planet’s Oxidation Processes
Geologists have discovered remnants of Earth’s mantle that have persisted for over 2.5 billion years. The ancient rocks were less oxidized than modern ones, indicating that they were exposed to extreme heat.
This discovery provides new insights into the geological history of our planet, challenging previously held beliefs about Earth’s oxidation processes and offering a peek into the past.
Earth’s mantle, the outer crust of our planet, is made up of different layers that consist of different types of rock. One of the most common types is an igneous rock high in silica content called peridotite.
In the past, when geologists compared prehistoric peridotite from Earth’s mantle with modern samples, they detected a major discrepancy.
Exposure to oxygen causes some of the rock to change through a process known as oxidation. The ancient remnants from Earth’s mantle were a lot less oxidized than samples from the modern mantle.
That means something must have changed between now and the Archean Eon, which was over 2.5 billion years ago.
Experts have proposed that changes in Earth’s oxygen may have led to the shift. Possibly, a large increase in oxygen resulted in greater oxidation.
However, new clues suggest that the oxidation change was caused by Earth’s mantle rocks being melted in extreme heat and lasting throughout billions of years.
The rocks were extracted from two spots—the Southwest Indian Ridge between southern Africa and Antarctica and the Gakkel Ridge near the North Pole.
chathuporn – stock.adobe.com – illustrative purposes only
At these ridges, the new crust has been forming slowly, giving researchers more of an opportunity to study rocks from Earth’s mantle.
The ridges are located at a far distance from each other. Despite this, the peridotites from both areas are less oxidized than modern mantle rocks. They also show evidence of being melted significantly more.
During the Archean Eon, the Earth’s mantle was much hotter. It is estimated that the mantle was more than 360 degrees Fahrenheit hotter than it is now. Some melting definitely would’ve occurred under such high temperatures.
Oxygen was also not yet in the atmosphere. The rocks formed during the Archean and carried on until they were pushed out along the ridges more than 2.5 billion years later.
The findings reshape Earth’s geological history. Instead of oxygen shifts occurring within the planet causing the differences in rock oxidation, it turns out that oxidation in Earth’s mantle has stayed fairly steady over time.
Mantle rocks that present fewer signs of oxidation are because the mantle used to be much hotter than it is today.
So, chemical changes that are observed in ancient rocks can be attributed to temperature changes as opposed to shifts in oxygen or other elements.
“It may be that cooling, rather than changes in the mantle’s bulk chemistry, is able to generate some of the chemical signatures we see in these rocks,” said Elizabeth Cottrell, geologist and chair of the National Museum of Natural History’s Department of Mineral Sciences.
The study was published in Nature.
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