It is difficult to find out what the 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 surrounded by a vast ocean, with very little or no mass of land. It was an extremely wet space rock.
So where the hell did all the water go? According to a team of researchers led by Harvard University planetary scientist Junjie Dong, the minerals deep inside the mantle slowly drank the Earth’s ancient oceans 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 article.
“We found that the water storage capacity in a hot, early mantle may have been less than the amount of water currently held by the terrestrial mantle, so that the additional water in the current mantle would have resided on the surface of early Earth and would have formed larger oceans.
“Our results suggest that it may be necessary to re-evaluate the long-term assumption that the volume of the surface oceans remained almost constant during geological time.”
It is believed that in the underground depths a large amount of water is stored in the form of compounds of the hydroxy group, formed by oxygen and hydrogen atoms. In particular, water is stored in two high-pressure forms of the volcanic mineral olivine, hydrated wadsleyite and ringwoodite. Wadsleyite samples at underground depths could 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 Earth’s mantle today to find out these storage capacities. Dong and his team saw another chance. They collected all available mineral physics data and quantified the water storage capacity of wadsleyite and ringwoodite over a wider temperature range.
The results showed that both minerals have lower storage capacities at higher temperatures. Because baby Terra, which formed 4.54 billion years ago, was much warmer internally than it is today (and its internal heat continues to decline, very slow, and has absolutely nothing to do with its external climate), means water storage the capacity of the mantle is now greater than before.
In addition, as more olivine minerals are crystallizing from the Earth’s magma over time, the mantle’s water storage capacity would also increase in this way.
Overall, the difference in water storage capacity would be significant, although 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 current mantle is 1.86 to 4.41 times the modern surface ocean mass.”
If the water stored in the current mantle is greater than its storage capacity in the archaic Aeon, between 2.5 and 4 billion years ago, it is possible that the world would be flooded and that the continents would be flooded, they said. find researchers.
This finding coincides with a previous study he found, based on the abundance of certain oxygen isotopes conserved in an early ocean geological record, that the Earth had 3.2 billion years ago. way less land than today.
If this is the case, it could help us answer hot questions about other aspects of Earth’s history, such as where life arose about 3.5 billion years ago. There is an ongoing debate about whether life first formed in oceans of salt water or freshwater ponds in land masses; if the entire planet were surrounded by oceans, this would solve this mystery.
In addition, the findings could also help us in the search for extraterrestrial life. Evidence suggests that oceanic worlds are abundant in our Universe, so looking for signatures from these wet planets could help us identify potentially hospitable worlds. And it could strengthen the case of seeking life in oceanic worlds in our own solar system, such as Europe and Enceladus.
No less important, it helps us better understand the delicate evolution of our planet and the strange, often seemingly inhospitable twists and turns that eventually led to the emergence of humanity.
The research has been published in AGU Advances.