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It’s hard to understand what Earth might have looked like in the early years before life emerged. Geological detectives have now obtained more evidence that it was rather different from the planet we live on today.
According to a new analysis of the characteristics of the Earth’s mantle over its long history, our entire world was once engulfed by a vast ocean, with little or no land mass at all. It was an extremely soggy space rock.
So where the hell has all the water gone? According to a team of researchers led by planet scientist Junjie Dong of Harvard University, minerals deep inside the mantle slowly absorbed ancient Earth’s oceans leaving what we have today.
“We calculated the storage capacity of water in the solid mantle of the Earth as a function of the mantle temperature,” the researchers wrote in their paper.
“We find that the water storage capacity in a warm, early mantle may have been less than the amount of water the Earth’s mantle currently holds, so the extra water in the mantle today would have resided on the surface of the early Earth and formed larger oceans.
“Our results suggest that the long-held assumption that the volume of surface oceans has remained nearly constant over geological time may need to be reassessed.”
In the underground depths, it is believed that a large amount of water is stored as compounds of the hydroxy group – made up of oxygen and hydrogen atoms. In particular, water is stored in two high pressure forms of the volcanic mineral olivine, hydrated wadsleyite and ringwoodite. Deep underground wadsleyite samples may contain about 3% H2O by weight; ringwoodite about 1 percent.
Previous research on the two minerals subjected them to the high pressures and temperatures of the modern Earth’s mantle to determine these storage capacities. Dong and his team saw another opportunity. They compiled all available data on mineral physics and quantified the water storage capacity of wadsleyite and ringwoodite over a wider range of temperatures.
The results showed that both minerals have lower storage capacities at higher temperatures. Because Baby Earth, which formed 4.54 billion years ago, was much hotter internally than it is today (and its internal heat is still decreasing, which is very slow and has absolutely nothing to do with its external climate), it means the water storage capacity of the mantle is now higher than it once was.
Additionally, as more and more olivine minerals crystallize from earth’s magma over time, the mantle’s water storage capacity would also increase in this way.
All in all, the difference in water storage capacity would be significant, even if the team was careful in their calculations.
“The bulk water storage capacity of the Earth’s solid mantle has been significantly affected by secular cooling due to the temperature-dependent storage capacities of its constituent minerals,” the researchers wrote.
“The mantle’s water storage capacity today is 1.86 to 4.41 times the modern surface ocean mass.”
If the water stored in the mantle today is greater than its storage capacity in the Archean Aeon 2.5 to 4 billion years ago, it is possible that the world was inundated and the continents submerged. , the researchers discovered.
This finding is in agreement with a previous study which found, based on an abundance of certain oxygen isotopes preserved in a geological record of the first oceans, that the Earth 3.2 billion years ago had path less land than today.
If so, it could help us answer burning questions about other aspects of Earth’s history, such as where life first appeared around 3.5 billion years ago. There is an ongoing debate as to whether life first formed in saltwater oceans or freshwater ponds on land; if the entire planet were swallowed up by the oceans, that would solve this mystery.
In addition, the results could also help us in the search for extraterrestrial life. Evidence suggests that oceanic worlds are plentiful in our Universe, so looking for signatures from these soggy planets could help us identify potentially hospitable worlds. And it could strengthen the case for the search for life on the oceanic worlds in our own solar system, like Europa and Enceladus.
Finally, it helps us better understand the delicate evolution of our planet and the strange, often seemingly inhospitable turns that ultimately led to the emergence of humanity.
The research was published in AGU Advances.
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