A Chemical Compound, Now Extinct, Preserved Earth's Water For 30 Million Years In Violent Era: Study
In a recent study, researchers have explored the origin of water. The authors suggested that a chemical compound, now extinct, could have preserved water deep underground in the violent era.
New Delhi: Scientists have always tried to find the answer to the question about what the origin of water on our planet is. Water is of utmost importance for plate tectonics, climate, life on Earth, and the potential habitability of other Earth-like planets.
In a recent study, researchers from the Skolkovo Institute of Science and Technology, Russia, have explored the origin of water. The study, conducted by a Skoltech professor and his Chinese colleagues, was recently published in the journal, Physical Review Letters.
How Water May Have Originated From A Chemical Compound
The authors suggested in the study that a chemical compound, now extinct, could have preserved water deep underground in the violent era. During the violent era, massive collisions must have evaporated the surface water on Earth.
Surface water is not only the all-important substance for the origin of life, but is also essential for stabilising a planet's climate over long periods of time. This is what allowed evolution to happen.
Rock plasticity, which is essential for plate tectonics, could be dramatically increased by even small amounts of water. Plate tectonics is a process that shapes the continents and oceans, and drives earthquakes and volcanism. Despite the huge Importance of water for the evolution of rocky planets like Earth, scientists do not know yet where water originated on Earth.
Why Comets Could Not Have Been The Source Of Earth's Water
Professor Artem R. Oganov of Skoltech, who co-authored the study, said in a university statement that some scientists thought water on Earth was seeded by comets, but that source seems to be very limited. This is because the isotope composition of water in comets is quite different from that on Earth.
Therefore, scientists concluded that if water did not come from above, it must have come from below, from deep within the mantle or even the core of the Earth. The first 30 million years in Earth's history were very violent because the planet was ceaselessly bombarded by asteroids, and even underwent a catastrophic collision with a Mars-sized planet.
A question arises that how did water survive the violent first 30 million years. The processes must have evaporated part of the Earth and what remained was molten at least seven hundred kilometres down, removing the water. Scientists, until now, did not know a stable compound that could lock up hydrogen and oxygen atoms and then release them as water, according to the statement. Water is made up of two atoms of hydrogen and one atom of oxygen.
Oganav and a group of researchers lead by Professor Xiao Dong of Nankai University, China, used Organov's crystal structure prediction method USPEX to discover a compound that could lock up hydrogen and oxygen atoms within the planet's interior.
Which Element Preserved Water In The Violent Era?
The scientists discovered a compound called Magnesium Hydrosilicate, with the formula Mg2SiO5H2, which is more than 11 per cent water by weight, the study said. It is stable at pressures of more than two million atmospheres, and at extremely high temperatures.
Pressures more than two million atmospheres exist in the Earth's core. However, everyone knows that the core is a metal ball, and has mostly iron. In this regard, the elements comprising Magnesium Hydrosilicate should not be available in the core, the statement said.
Oganov explained that this is wrong, because there was no core at that time, according to the statement. He said that in the beginning of Earth's existence, the planet had a more or less evenly distributed composition, and it took the iron roughly 30 million years from when the planet formed to seep down to its centre. The iron pushed the silicates up into what we now call the mantle, Oganov said.
For 30 million years, part of Earth's water was safely stored away in the form of hydrosilicates at the depths of the present-day core, the study said. The Earth withstood the heaviest phase of asteroid bombardment during that time. The hydrosilicates had been pushed into lower-pressure areas by the time the core formed.
In the lower-pressure areas, the hydrosilicates became unstable and decomposed, according to the study.
The Compound Decomposed To Form Water
This process led to the production of magnesium oxide and magnesium silicate that make up the mantle today, along with water, which started on its 100-million-year-long journey to the surface of Earth, according to the study.
Oganov said that Earth, in the meantime, was being pummeled by asteroids and even a protoplanet, according to the statement. He said that the water was safe, because it had not yet made its way to the surface.
Oganov said this is also a story about how a material that existed for a brief moment on the planetary timescale had a massive impact on Earth's evolution.
How The Hypothesis Has Implications For Water On Other Celestial Bodies
The new hypothesis of water origin can explain the presence of water on other celestial bodies also. Oganov said that Mars, for example, is too small to produce pressures necessary to stabilise Magnesium Hydrosilicate, and this explains why the Red Planet is so dry and means that whatever water exists on Mars, likely came from comets, according to the statement.
The authors also considered planets outside our solar system. Xiao Dong said that an exoplanet has to have a stable climate to be habitable, and this requires both continents and oceans. So, there has to be water, but not too much, he said.
He added that there was an estimate that for an Earth-like planet of any size to be habitable, it should have no more than 0.2 per cent water by weight.
Xiao Dong explained that their results imply that for large Earth-like planets, called 'super-Earths', the story is likely different. This is because in such planets, pressures stabilising the Magnesium Hydrosilicate must exist even outside the core, locking up large amounts of water indefinitely.
Quoting Xiao Dong, the statement said that as a result, super-Earths can have a much greater water content and still support the existence of exposed continents.
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