Life is a miracle in the universe, and so far, we have never found any trace of life that can be determined outside of Earth, and water is an indispensable material basis for all known life on Earth, so water is also called the "source of life".
Studies have shown that water was abundant on Earth more than 4 billion years ago. So the question arises: Has the Earth's water been used for more than 4 billion years, and has it become less? The scientific community is also very interested in this question, in fact, in the past research work, scientists have found the answer on a stone, what is going on? And see the breakdown below.
The first thing to say is that the earth is not a completely closed system, in addition, the earth's gravity is not as strong as imagined, in the earth's atmosphere, although the earth can rely on gravity to bind heavier elements such as oxygen and nitrogen, but also can bind water molecules, but for very light elements such as hydrogen and helium in the atmosphere, the earth's gravity can not form an effective bondage on it.
We all know that water molecules are actually made of hydrogen and oxygen combined through covalent bonds, so if there is some mechanism that can decompose water molecules into hydrogen and oxygen, it is likely that there will be a situation such as "hydrogen escape, oxygen stays", and if this really happens, it means that there is less water on the earth.
Such mechanisms exist on Earth, for example, short-wave radiation in sunlight can break the covalent bonds inside water molecules, thereby breaking them into hydrogen and oxygen, which is also known as "photolysis".
In fact, when water vapor in the Earth's atmosphere spreads to the upper atmosphere, it may be "photolyzed" by sunlight into hydrogen and oxygen, after which hydrogen may continue to rise due to its smaller density and eventually escape from the top of the atmosphere.
It should be pointed out that under the action of The Earth's gravity, most of the water vapor in the atmosphere does not spread to the upper atmosphere, and according to scientists' calculations, only about 95,000 tons of hydrogen escape from the top of the Earth's atmosphere every year.
This amount can be said to be insignificant compared with the amount of water on the earth, that is to say, the loss of water on the earth for this reason is not much, on the other hand, the earth will capture some free hydrogen when running in the cosmic space, and some small celestial bodies (such as comets) will also bring some water to the earth, which is enough to make up for the loss of water on the earth due to "photolysis", so the earth can still achieve dynamic "break-even".
However, water on Earth may also be reduced by other mechanisms, such as when seawater in the ocean seeps deep underground through gaps in the rocks on the ocean floor, it may have a series of reactions with high-temperature magma and the crystalline bedrock in it, which in turn will decompose water molecules into hydrogen and oxygen, which scientists call "Methanogenesis", as shown in the following figure.
It should be noted that the figure above shows only the net effect of the "methanogenic process", and its specific process needs to involve professional geochemical knowledge, which we will not expand here. Simply put, this series of reactions can break down a part of the water molecules in seawater into hydrogen and oxygen, which rises to the surface of the ocean and then into the Earth's atmosphere.
The modern Earth's atmosphere is so rich in oxygen that most of this hydrogen will be re-oxidized into water in the lower atmosphere without escaping from the top of the Earth's atmosphere, but the Earth's atmosphere has not always been as full of oxygen as it is now, in fact, before the "Great Oxidation Event" about 2.6 billion years ago, the oxygen content in the Earth's atmosphere was so low that it was negligible.
That is, before there is enough oxygen in the Earth's atmosphere, the hydrogen produced through the "methanogenic process" will escape in large quantities from the top of the Earth's atmosphere, and there will be less water on the Earth.
Hydrogen has three isotopes, the only stable existence of "deuterium" and "deuterium", scientists found that in the above "methanogenic process", "deuterium" efficiency is much higher than "deuterium", which means that those who escape through the "methanogenic process" and escape more "deuterium" than "deuterium", and as this process continues, the proportion of "deuterium" and "deuterium" in the ocean will change.
On this basis, we only need to know the proportion of "deuterium" and "deuterium" in the Earth's oceans more than 4 billion years ago, and then use relevant theories to build models, and compare and analyze them with the proportions of "deuterium" and "deuterium" in the modern Earth's oceans, we can know how much hydrogen the Earth lost in the past, and then calculate how much water on the Earth has become less in the past (after all, most of the water on Earth is in the ocean).
Seeing this, I believe that everyone has guessed what the aforementioned "scientists find the answer on a stone" means, yes, scientists have found the proportion of "deuterium" and "deuterium" in the ancient Earth's ocean on a stone.
Found in the geological layer of western Greenland, this stone is a serpentine formed about 4 billion years ago, this stone is usually formed on the seabed, mid-ocean ridge and subduction zone, the local shell and the high temperature seawater circulating through the seabed crevices, it may form serpentine, because in the formation of the serpentine will absorb a large amount of water, the proportion of "deuterium" and "deuterium" in the seawater will be preserved for a long time.
Through the study of this stone, the scientists concluded that the modern Earth's oceans were about 26% smaller in size than the early Earth, in other words, almost 1/4 less water on Earth.
(The picture shows what the stone looks like under a microscope.)
That's a surprising answer, but we don't have to worry about the water on modern Earth that will continue to run out in large amounts.
As mentioned earlier, the atmosphere of the modern Earth has long been filled with oxygen, which means that on the modern Earth, the hydrogen produced through the "methanogenic process" will basically be oxidized into water in the lower atmosphere and will not escape from the top of the Earth's atmosphere.
Taking a step back, even if a very small part of the escape is escaped, the water on the earth is reduced by a little less, and this water is much less than the water lost on the earth due to "photolysis", which can be completely replenished by free hydrogen in space and small bodies rich in water, so as to maintain a dynamic balance as a whole.
Resources:
Emily C. Pope, Dennis K. Bird, and Minik T. Rosing. Isotope composition and volume of Earth's early oceans. DOI: 10.1073/pnas.1115705109
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