It’s hard to figure out what Earth would have been like in the early years before life came up. Geological detectives have now amassed more evidence that it was quite different from the planet we live on today.
According to a new analysis of the mantle characteristics throughout its long history, our entire world was once inundated by a vast ocean, with very little or no land masses at all. It was an extremely swampy space rock.
So where the hell has all the water gone? According to a team of researchers led by Harvard University planetary scientist Junjie Dong, minerals deep in the mantle slowly drank up the oceans of the ancient Earth to leave what we have today.
“We calculated the water storage capacity in the Earth’s solid mantle as a function of mantle temperature,” the researchers wrote in their paper.
“We find that the water storage capacity in a hot, early mantle may have been less than the amount of water the Earth’s mantle currently contains, so the extra water in the mantle would have been on the surface of the early Earth today and formed larger oceans. .
“Our results suggest that the long-held assumption that the volume of the oceans at the surface remained nearly constant over geologic time may need to be reassessed.”
Deep underground, it is thought that a lot of water is stored in the form of hydroxy group compounds – consisting of oxygen and hydrogen atoms. In particular, the water is stored in two high-pressure forms of the volcanic mineral olivine, hydrous wadsleyite and ringwoodite. Deep subterranean wadsleyite samples may contain about 3 weight percent H2O; 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 discover these storage capacities. Dong and his team saw another opportunity. They collected all available mineral physical data and quantified the water storage capacity of wadsleyite and ringwoodite over a wider temperature range.
The results showed that the two minerals have a lower storage capacity at higher temperatures. Since baby Earth, which was formed 4.54 billion years ago, was much warmer internally than it is now (and the internal heat is still declining, which is very slow and also has absolutely nothing to do with the external climate), this means the mantle’s water storage capacity is now higher than it ever was.
In addition, as more olivine minerals crystallize from Earth’s magma over time, the mantle’s water storage capacity would also increase that way.
Overall, the difference in water storage capacity would be significant, even if the team was conservative with its calculations.
“The bulk water storage capacity of the solid mantle was significantly affected by secular cooling due to the temperature-dependent storage capacity of the mineral components,” 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 exceeds 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 inundated, the researchers found.
This finding is in agreement with a previous study that found, based on an abundance of certain isotopes of oxygen preserved in a geological record of the early ocean, that the Earth had 3.2 billion years ago. way less land than now.
If so, it could help us answer burning questions about other aspects of Earth’s history, such as where life originated about 3.5 billion years ago. There is an ongoing debate as to whether life first originated in saltwater oceans or freshwater ponds on landmasses; if the entire planet were inundated by oceans, it would solve that mystery.
In addition, the findings may also help us in the search for extraterrestrial life. Evidence suggests that ocean worlds are abundant in our universe, so searching for signatures from these boggy planets could help us identify potentially hospitable worlds. And it could bolster the arguments for seeking life on ocean worlds in our own solar system, such as Europa and Enceladus.
Last but not least, it helps us to better understand the delicate evolution of our planet, and the strange, often seemingly inhospitable twists along the way that eventually led to the emergence of humanity.
The research is published in AGU advances