Emily Chan
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.
