It’s hard to figure out what Earth might have been like in the early years before life emerged. Geological detectives have now obtained more evidence that it was quite different from the planet we live on today.
According to a new analysis of the characteristics of the Earth’s mantle throughout its long history, our entire world was once enveloped by a vast ocean, with little or no landmass. It was an extremely soggy space rock.
So where the hell did all the water go? According to a team of researchers led by planetary scientist Junjie Dong of Harvard University, minerals from within the mantle slowly drank the oceans of ancient Earth to leave what we have today.
“We calculate the water storage capacity in the solid mantle of the Earth as a function of the temperature of the mantle,” the researchers wrote in their paper.
“We found that the water storage capacity in a warm, early mantle may have been less than the amount of water currently contained in the Earth’s mantle, so the additional water in the current mantle would have resided on the surface of the Earth. Primitive Earth and formed larger oceans.
“Our results suggest that the long-standing assumption that the volume of the ocean surface remained nearly constant over geologic time may need to be reassessed.”
Deep underground, a large amount of water is believed to be stored in the form of hydroxy group compounds, 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-sea wadsleyite samples could contain about 3 percent 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 collected all available mineral physics data and quantified the water storage capacity of wadsleyite and ringwoodite over a broader range of temperatures.
The results showed that the two minerals have lower storage capacities at higher temperatures. Because Baby Earth, which formed 4.54 billion years ago, was much warmer internally than it is today (and its internal heat keeps decreasing, which is very slow and has absolutely nothing to do with its external climate either. ), it means that the water storage capacity of the mantle is now greater than before.
Furthermore, as more olivine minerals crystallize in Earth’s magma over time, the mantle’s water storage capacity would increase that way as well.
Overall, the difference in water storage capacity would be significant, even though the team was conservative with their calculations.
“The bulk water storage capacity of the Earth’s solid mantle was significantly affected by secular cooling due to the temperature-dependent storage capacities of its constituent minerals,” the researchers wrote.
“The water storage capacity of the mantle 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 Eon, between 2.5 and 4 billion years ago, it is possible that the world was flooded and the continents were flooded, the researchers found.
This finding is in agreement with an earlier study that found, based on an abundance of certain oxygen isotopes conserved in a geological record of the early ocean, that the Earth had 3.2 billion years ago. path less land than today.
If this is the case, it could help us answer burning questions about other aspects of Earth’s history, like where life emerged about 3.5 billion years ago. There is an ongoing debate as to whether life first formed in saltwater oceans or freshwater ponds on land masses; if the entire planet were enveloped by oceans, that would solve that mystery.
Furthermore, the findings could also help us in the search for extraterrestrial life. Evidence suggests that ocean worlds are abundant in our Universe, so looking for signatures from these soggy planets could help us identify potentially hospitable worlds. And it could make the case for looking for life on the ocean worlds of our own Solar System, like Europa and Enceladus.
Not least, it helps us better understand the delicate evolution of our planet and the strange, often seemingly inhospitable twists and turns on the path that ultimately led to the rise of humanity.
The research has been published in AGU Advances.