In fact, there is no accepted answer to this question in the scientific community. There are two main theories, namely "endogenous theory" and "exogenous theory".
The first is "endogenous theory". Geologists who believe in this theory believe that water has been one of the basic components of the earth since its birth. Hydrogen and oxygen are the basic elements of the earth. In the process of their formation, these two elements react chemically under certain conditions to produce water.
In the early days of the earth's formation, the geological structure of the earth was unstable, the crustal movement was fierce, and a large number of volcanoes erupted a lot of magma, which led to the extremely high surface temperature and could not preserve a large amount of liquid water. At this time, most of the water can only exist in the mantle or crust. Of course, some water in the primitive earth's atmosphere existed in gaseous form.
With the stability of the earth, the surface temperature began to slowly decrease, and a large number of water molecules formed a large amount of liquid water when they were cold, and more liquid water began to appear on the surface. In this process, the water in the mantle is also brought into the earth's atmosphere with the eruption of magma, and finally falls to the earth's surface through rainfall. Therefore, scientists believe that at some time on the primitive earth, there was super rainfall that lasted for millions of years.
A rain that has rained for millions of years has collected a lot of liquid water on the earth's surface and gradually formed rivers, lakes and oceans. Based on this, scientists believe that the reason why water on the earth can flow continuously for more than 4 billion years is because there are a lot of water resources stored in the mantle. In the past 400 million years, water has been pouring out of the mantle to replenish the biosphere, making the water on the earth's surface never exhausted.
It is worth noting that the water on the primitive earth is very different from today's water. According to the calculation and estimation of scientists, the water content of the ocean is now more than 1 times that of the original ocean. Not only that, the water in the primitive ocean is weakly acidic, and its taste is different from the salty seawater now. This is because a large number of volcanic eruptions on the primitive earth led to the high content of acid gases such as sulfur dioxide (SO2) and hydrogen sulfide (H2S) in the atmosphere, so almost all the rainfall in the world at that time was acid rain.
After years of scouring, a large amount of sodium chloride (NaCl) was precipitated from minerals, which made the salt content of seawater higher and higher, and finally formed the present seawater.
The second theory is "exogenous theory". Astronomers believe that most of the water on our planet comes from outer space. In the early days of the birth of the earth, meteorites can be said to be frequent visitors to the earth. Scientists believe that these meteorites generally contain a lot of water, and with the passage of time, a lot of liquid water has been formed.
In addition to meteorites, the solar wind also played a considerable role. After the solar wind reaches the earth's atmosphere, a large number of nuclei such as oxygen nuclei, hydrogen nuclei and carbon nuclei carried by it combine with electrons in the atmosphere to form hydrogen atoms, oxygen atoms and carbon atoms. Under the action of chemical reaction, these atoms form water molecules, which liquefy to form precipitates and reach the surface.
At present, neither of these two statements can convince anyone, that is to say, there is no only definite conclusion about how the water on the earth came from. But we can be sure that although the water on the earth seems to occupy 765,438+0% of the surface area, only 2% of it can be consumed by human beings, so it can be said that water resources are very precious.
With the improvement of human industrial level and living standard, a large number of industrial wastewater and domestic sewage are discharged, which leads to a lot of pollution, and the water resources available for us are gradually decreasing. You know, the saying that water is the source of life is no joke. No one can survive without water.