The "origin of water" on Earth has long been an open question. However, the scientific team at lawrence Livermore National Laboratory (LLNL) in the United States published their new findings in the Proceedings of the National Academy of Sciences (PNAS), studying the lunar rocks brought back by the American Apollo, helping scientists to lock in the answer to the "origin of Earth's water".
If you look at it from space, the Earth is like a blue star like a water ball, with an ocean area of about 360 million square kilometers, accounting for 71% of the Earth's surface area, far exceeding the land area, with an average water depth of about 3795 meters and an ocean water content of 1.33 billion cubic kilometers. So where does all this water come from?
There have always been two mainstream views on the "origin of water", namely: the autologous theory and the exogenous theory. The former refers to the fact that the water on the earth is "born" and comes with it after the formation of the earth, and the latter refers to the fact that the water on the earth is sent by celestial bodies in outer space. So what is the basis for this?
Self-derived
According to the study, 4.6 billion years ago, there was a 2-light-year-long molecular cloud near the current solar system, and for some reason, the gravitational equilibrium here was broken. Thus, under the action of gravity, the material in the molecular cloud gathered together to form the sun, and the remaining corner fragments formed other celestial bodies in the solar system, and the original Earth formed at that time.
Some scientists believe that water already exists in the process of formation of the earth, but the temperature at that time is very high, resulting in water not being liquid, but evaporating, becoming part of the atmosphere, but due to the existence of the earth's gravity, these waters are not out of the control of the earth.
In addition, they believe that some water in the form of hydrogen separation, hydroxyl and other forms of nebula material that makes up the earth has hydrated, thus being locked in the mineral lattice.
Later, as the earth gradually cooled, the water vapor in the atmosphere condensed into liquid water and fell to the ground, forming a heavy rain that lasted for millions or even tens of millions of years, and finally this heavy rain converged into the primordial ocean.
Is there any evidence for this claim?
Scientists have discovered a type of rock called spinel olivine, also known as Lynnwood stone.
This rock is the main rock-making mineral in the transition zone of the mantle layer. Scientists have found that in spinel peridots 200 kilometers above the ground, there are about 2,000 water molecules for every 1 million crystalline molecules.
Not only that, scientists have also found that in the formation 410 to 660 kilometers from the ground, the spinel peridot here has a higher water content, reaching 1.5 water molecules per 100 crystal molecules. Some people may question: why is it believed that this water was brought by the earth at the beginning of the formation of the earth?
At first, scientists weren't sure. However, zircon fragments dating back 4.4 billion years were later found in Australia. The inside of this stone is watery, and it comes from the surface. The discovery of zircon fragments confirms that soon after the birth of the Earth, there was already water on the surface.
Exogenous said
In addition to the self-origin theory, another part of scientists believe that the Earth's origin comes from comets and meteorites. So where did this conclusion come about?
We all know that the molecular formula of water is: H O, which is composed of 2 hydrogen atoms and 1 oxygen atom. Among them, there is only 1 proton in the hydrogen atom, which we also call: krypton. However, in fact, the water molecule is not exactly like this, the hydrogen atom has other isotopes, for example, there are 1 proton and 1 neutron in the nucleus called: deuterium (denoted by the symbol D, D O), or 1 proton and 2 neutrons called : tritium (denoted by the symbol T, T O).
Scientists have found that if the water on Earth all comes from the same source, then the ratio to deuterium and deuterium (for convenience, we call this concept: D/H ratio) should be constant, and if the source of water is different, the D/H ratio will change. Scientists have found that the D/H ratio of water on Earth is maintained at about 156 out of 1 million deuterium atoms.
They compared the D/H ratios in various celestial bodies in the solar system and early nebula material, and found that the D/H ratio of water on Earth was similar to the D/H ratio of a carbonaceous chondrite meteorite, which is not only rich in water, but also accounts for 86% of the total number of meteorites in the solar system.
Therefore, scientists who support the exogenous theory believe that the water on Earth is likely to be sent by this carbonaceous chondrite meteorite and other asteroids and comets with the same D/H ratio. There is another view that a variety of Earth objects have been sent, and the D/H ratio has finally been adjusted to exactly what it is now.
Lunar Revelation
Until then, the two factions of views had been deadlocked, and neither had been able to convince the other. So scientists set their sights on the moon. Many people may wonder, what is the matter with the water on the earth and the moon?
In fact, according to the current mainstream theory, 30 million years after the formation of the Earth, there was a planet called Thea that had been moving around the Earth's orbit, and as a result, it accidentally hit the Earth, and the material of the planet was integrated into the Earth due to the impact, and the impact also caused a large amount of material to be thrown into space, and these materials moved around the Earth. Later, under the influence of gravity, it converged to form the moon.
That is to say, the Earth and the Moon are the products of the combined formation of the primordial Earth and the Thea impact, and the two sides are "you have me, I have you". Therefore, the study of "the origin of water on Earth" is also to some extent the study of "the origin of water on the moon".
Based on the study of the isotopic composition of lunar rocks (rubidium-87/strontium-87), scientists have found that water on Earth is either innate or brought about by the existence of a celestial body containing a large amount of pure water.
Greg Brennecka, a cosmic chemist, said the study directly ruled out the possibility that meteorites or asteroids would bring water to Earth, pointing to earth's "innate" options for the origin of water. Mainly because, whether it is a meteorite or an asteroid, it only contains water, but it does not contain a large amount of pure water.
That is to say, based on the study of lunar rocks, scientists have directly hammered out the previously debated question of the "origin of water", and the exogenous theory has been excluded after the publication of this study, so only the self-derived theory can be established.