Scientists have uncovered the mystery of the origin of water on earth. Hypotheses for the formation of the hydrosphere
Astronomers Sean Raymond (University of Bordeaux, France) and Andre Isidoro (University of São Paulo Julio de Mesquita Filho, Brazil) described a possible mechanism for how water got to Earth. Their research was published in the journal Icarus, available on the website arXiv.org, and the first author spoke about it on his blog.
Scientists believe that water on Earth and celestial bodies from the asteroid belt between the orbits of Mars and Jupiter has a common origin, primarily associated with the formation of gas giants in the Solar System.
Oceans cover three-quarters of the Earth, but the water on the surface accounts for only one four-thousandth of the planet's total mass. Water is in both the mantle (in the form of hydrated rocks) and in the Earth's core. How much there is is unknown, probably ten times more than on the surface.
In general, there is little water on Earth, and there is also some on the Moon, Mercury, Venus and Mars. Perhaps Venus and Mars once had more water. The main reservoir of water within the orbit of Jupiter is the asteroid belt.
In the inner part of the main belt, within 2-2.3 astronomical units from the Sun, asteroids of class S (rocky) predominate, in the outer part - class C (carbonaceous). There are other asteroids, but not so massive. Class C asteroids contain more water than class S - about ten percent (by mass).
The origin of water can be determined by conducting an isotopic analysis of the hydrogen contained in the water of various celestial bodies. In addition to protium, hydrogen with a nucleus of one proton, deuterium (with a proton and a neutron) and very rarely tritium (with a proton and two neutrons) are found in nature.
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Isotope analysis reveals several features. The Sun and gas giants have a ratio of deuterium to tritium that is one to two orders of magnitude less than that of the Earth. But for class C asteroids this figure is almost the same as for our planet. This indicates a common origin of water.
Comets in the Oort cloud have a ratio of deuterium to protium that is approximately twice that of Earth. There are three comets within the orbit of Jupiter, for which this parameter is close to that of Earth, but there is also one comet where this parameter is 3.5 times greater. All this may mean that the water on comets has different origins and only part of it was formed in the same way as on Earth.
Planets form around young stars in giant disks of gas and dust. Closer to the star it is too hot, so planets rich in silicon and iron appear there. Farther away from the star it is colder, where celestial bodies can also form from water ice. The Earth arose in that part of the protoplanetary disk where rocky celestial bodies were born, without water. This means that she came to the planet from outside.
On the other hand, S and C class asteroids are too different for them to form next to each other. In addition, the boundary beyond which icy celestial bodies formed constantly moved during the evolution of the Solar System, and Jupiter played a decisive role in this.
Jupiter and Saturn are believed to have formed in two stages. At first they were solid celestial bodies, several times heavier than the modern Earth, and then began to capture gas from the protoplanetary disk. At this stage, the mass and size of the planets increase sharply, the giants clear space for themselves in the protoplanetary disk.
Large Jupiter and Saturn were then surrounded by small planetesimals - the predecessors of protoplanets. As Jupiter and Saturn grew, the orbits of the planetesimals stretched, crossing the inner Solar System and moving away from the star. But Jupiter and Saturn still attracted gas from the protoplanetary disk, as a result of which, as the simulation showed, the orbits of the planetesimals were corrected by Jupiter and moved into the region of the modern asteroid belt.
Saturn arose later than Jupiter, and its formation led to a new migration of planetesimals, although not as significant. The main conclusion of the researchers is that class C asteroids appeared in the belt from the orbits of the gas giants after Jupiter and Saturn completed their formation (although some planetesimals could reach the orbit of Neptune).
According to scientists, water came to our planet during the formation of the asteroid belt thanks to planetesimals of a certain type (namely, class C asteroids) with highly eccentric (elongated) and unstable orbits that intersected the trajectory of the Earth. Hydrogen isotope analysis is the main confirmation of this.
The delivery of water to Earth was almost completed with the formation of Jupiter and Saturn and the disappearance of the protoplanetary disk. Thus, the popular hypothesis that explains the small size of Mars by the migration of Jupiter deeper into the Solar System correlates with the mechanism of enrichment of Earth with water. The appearance of water, the most important source of life on Earth, in the inner Solar System (both on rocky planets and in the asteroid belt) turns out to be simply a side effect of the growth of Jupiter and Saturn.
Water is a binary inorganic compound whose molecule consists of two hydrogen atoms and one oxygen atom. Under normal conditions, it is a colorless liquid (in small volumes), taste and odor. Water exists under Earth's conditions in three states of aggregation, as well as on hydrophilic surfaces - in the form of liquid crystals
Since ancient times, water has been treated with respect, considering it one of the Elements of nature - air, water, earth and fire. The ancient Greek philosopher and mathematician Thales of Miletus (624 - 546 BC) argued that water is the most important of them: "... everything from water and into water decomposes." Organic life requires water and it is believed that it served as the place of its origin. About 71% of the earth's surface is covered with water - 361.13 million square kilometers. The oceans account for 96.5% of all water, !.7% is groundwater, 1.7% is glaciers and ice caps of Antarctica and Greenland. A little is represented by rivers, lakes and swamps, 0.001% is in the clouds. Most of the earth's water is salty. The share of fresh water is approximately 2.5%, with most of it contained in glaciers and groundwater. Less than 0.3% of all fresh water in rivers, lakes and the atmosphere. There are several theories about the possible appearance of water on our planet. Conventionally, they can be divided into two groups - the terrestrial origin of water and the cosmic origin of water.
Ocean inside the planet. Terrestrial origin of water
One of the hypotheses of terrestrial origin considers the appearance of water, among other chemical elements, during the hot phase of the formation of the planet. Water vapor, along with other resulting gases, erupted from cracks in the cooling crust, forming the planet's cloud cover. When the temperature dropped, condensation began, rain began to pour, filling natural depressions and depressions, forming reservoirs.
Another hypothesis speaks of the heating of the planet as a result of intense volcanic activity during the youth of the Earth. As we now know, the bottom of modern oceans was the site of ancient volcanoes. In the Earth's mantle at a depth of 50 km - 70 km, water vapor began to arise from hydrogen and oxygen ions. However, the high temperature of the mantle did not allow it to enter into chemical compounds with matter. Under pressure, steam was squeezed into the upper layers of the mantle and into the crust. In the crust, the temperature is lower and chemical reactions between minerals and water begin. The result of this process was the loosening of rocks, the formation of cracks and voids. They filled with water. The pressure turned them into cracks and through them water rushed to the surface. Hot water in the bark easily dissolved alkalis and acids. This mixture corroded everything around it, turning into a kind of brine that gave the seas a salinity. The brine was spreading under the granite base of the continents. It could not penetrate granite; the porous structure retained the mixture, blocking the path of water. If this is so, then under the continents at a depth of 12 km - 20 km there are oceans of compressed water saturated with salts and metals. It is possible that such oceans are also located under the basalt ocean floor. This hypothesis is supported by the inexplicable sharp increase in the speed of seismic waves, which was recorded at a depth of the same 12 km - 20 km, where the supposed granite-brine interface, the boundary of a sharp change in the physico-chemical properties of the substance, should be located. Continental drift indirectly supports this hypothesis - perhaps the brine oceans play the role of a lubricant along which the continents slide.
Another hypothesis for the terrestrial origin of water is that water is formed as a result of the release of hydrogen as a result of the breakdown of metal-hydrogen compounds, that is, the restoration of metal structures in the mantle and core of the Earth. This process causes the expansion of the Earth, which is actually recorded - so Moscow and St. Petersburg are floating east at a speed of 10 cm per year, and Hamburg (in the center of Europe) remains in place, that is, Europe is expanding. The released hydrogen captures oxygen atoms along the way from the depths and water vapor breaks out to the surface. As water condenses, it fills cracks in the crust, forming oceans.
Water was delivered from space
And the following hypotheses suggest the cosmic origin of water. One claims that water was brought to the planet by comets, asteroids or meteorite bodies. Indeed, meteorites contain up to 0.5% water. Few? Only at first glance. However, if the Earth was formed from similar cosmic debris (impact and subsequent connection), then with a total mass of six by ten to the twenty-first power of tons, it should contain three by ten to the nineteenth power of water. The total mass of water on the planet, according to modern data, is about fourteen to ten to the ninth power tons. It turns out that the Earth is saturated with water from the center to the surface like a sponge.
Another space hypothesis claims that it was not the water itself that was delivered from space, but its components. A shower of charged particles continuously rains down on the Earth. Among them, a significant proportion are protons - the nuclei of the hydrogen atom. In the upper layers of the atmosphere, capturing electrons, they turn into hydrogen. Which reacts with oxygen in the atmosphere and forms a water molecule. One and a half tons of water per year. The process did not start yesterday. Perhaps he was walking at a different speed before? So that water flooded the entire surface of the planet, reaching the mountain peaks? And then she went into the depths, leaving the oceans...
There are many hypotheses, it is difficult to confirm them. The incoming data from recent studies are often contradictory and it is still very difficult to come to a consensus. Here are some conclusions of modern experts. Professor Vasily Ivanovich Ferronsky, chief researcher at the Institute of Water Problems of the Russian Academy of Sciences, studied the oxygen isotope content in ocean waters and in ancient rocks of the Earth - granites and basalts. The experiment showed that the rocks contain significantly more of this isotope. This allows us to assert that water could not have been formed due to its release from the bowels of the Earth.
Comet Hartley 2's water is identical to Earth's
Data from the Rosetta space module, which studies the nucleus of comet Churyumov-Gerasimenko (67P), indicate that the deuterium content in cometary vapor significantly exceeds the parameters of terrestrial water. This means that the earth’s water is not from comets. However, not everything is clear here. Yes, in comets from the Oort cloud (at the edge of the solar system) the water does not coincide in composition with that on Earth, but there is also a family from the Kuiper belt (between Neptune and Uranus). And observations using the Herschel orbital telescope indicate that the water contained in comet Hartley-2 (Kuiper belt) is completely identical to that on Earth in isotopic composition. This means that Earth's water can be cometary...
Astronomers report that they have discovered water in protoplanetary disks. The most interesting part of the disk is the middle part, where the water can be warm. Such a supply of warm liquid water in the future could become the beginning of the oceans and helps explain the emergence of water on Earth without the participation of asteroids and comets. By the way, about asteroids. One of them, located in the main belt, 24 Thermis, is covered with a thick layer of frost. Asteroids of this type could well deliver it to Earth. It turns out that it is too early to discount asteroids.
The oldest water in the Universe has been discovered at a distance of 11 billion light years from Earth. Astronomers believe that this is a common conjunction not only in the present, but also in the early Universe, no more than 2 billion years old.
Scientists in Japan believe that the early Earth had a dense hydrogen atmosphere, which interacted with oxygen in the planet's structure to form water. On the other hand, Japanese geologists talk about entire layers of hydrogen in the earth’s structure, which interacted with oxygen from the mantle... Yeah... In a word, “... dark is the water in the clouds of air” (Old Testament, Psalter, ps. 17 , art. 12).
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MOSCOW, January 12 - RIA Novosti. The oldest rocks of the Earth from a Canadian island in the Arctic told scientists that the water of our planet existed on its surface originally, and was not brought by comets or asteroids, according to an article published in the journal Science.
“We found that the water molecules in the samples of these rocks contained few atoms of deuterium, heavy hydrogen. This suggests that it came to Earth not after it had formed and cooled, but along with the dust from which it was formed our planet. Most of the water in this dust evaporated, but there was enough leftover to form the Earth's oceans," said Lydia Hallis from the University of Glasgow (Scotland).
Today, planetary scientists believe that the Earth’s waters are of “cosmic” origin. Their source, according to half of them, is comets, while other astronomers believe that the water reserves of our planet were “brought” to it by asteroids.
Hallis and her colleagues showed that our planet's oceans may in fact be filled with its own water by studying samples of Earth's oldest basalts found in Baffin Land, Canada, in 1985.
These fragments of the Earth's mantle, as the geologist explains, contain so-called inclusions - small balls of crystals of refractory rocks that formed at the dawn of the solar system, about 4.5-4.4 billion years ago. Due to the fact that they never left the bowels of the Earth and did not mix with the rocks of the earth’s crust, they contain the primary matter of our planet.
Hallis's group decided to take advantage of this fact to study the isotopic composition of the water contained in these inclusions and compare it with the values in fractions of hydrogen isotopes that are typical for the waters of the Earth today and for asteroids and comets.
Scientists: Jupiter could destroy “super-Earths” in the young solar systemOur Solar System may have contained one or more large Earth-like planets in the early stages of its formation, which were later absorbed by the Sun as a result of the migrations of Jupiter.As it turned out, the primary rocks of the Earth contained unusually little deuterium, heavy hydrogen, noticeably less than is contained in the waters of modern oceans and in the matter of small celestial bodies. This suggests that the source of water was the primary matter of the gas-dust disk from which the Earth and all other inhabitants of the Solar System were born.
Why is this so? Initially, as Hallis explains, the primordial matter of the solar system contained very little deuterium. Deuterium is heavier than “ordinary” hydrogen, and therefore its atoms evaporate into space from the surface of the Earth or other celestial bodies much more slowly than simple protons. Therefore, the more time water spends in open space, the less deuterium it will contain. This explains why the small amount of deuterium in water in samples of these rocks indicates the “terrestrial” origin of water in the oceans of our planet.
Today, very few scientists believe that water and most of the gases in the Earth’s atmosphere could have arisen on our planet “independently.” This is explained by the fact that the Earth is located in the so-called hot part of the protoplanetary disk, where water ice and other frozen volatile substances were gradually destroyed under the influence of ultraviolet and other rays of the newborn Sun.
On the other hand, in recent years, planetary scientists have found a lot of evidence and theoretical evidence in favor of the fact that the Earth and some other Earth-like planets of the solar system could have formed in a more distant and cold part of the protoplanetary disk, and then were “driven” from their place into modern orbits Jupiter and Saturn. The discovery by Hallis and her colleagues may be another argument in favor of this “migration” theory.
How and when did water appear on Earth? Scientists are still discussing this topic, but no one has yet given an accurate and logically proven answer. To date, there are several assumptions about how the liquid could have formed on the planet. Among them there are both completely absurd and quite logical hypotheses, but so far none of them is completely reliable.
How did water appear on Earth? Briefly about the main hypotheses
Water plays a big role in maintaining life on the planet, since it is the main internal environment of any organism. On average, a person can survive without water for no more than three days, and the loss of 15-20% of fluid often leads to death.
How did water appear on Earth? Hypotheses for the formation of this substance are few, and none of them have yet received reliable evidence. Nevertheless, only they can somehow explain the formation of the hydrosphere of our planet.
Hypothesis of the cosmic origin of water
A group of researchers hypothesized that the water appeared along with numerous falling meteorites. This happened about 4.4 billion years ago, when the planet was still in its infancy, and its surface was dry, devastated land, over which an atmosphere had not yet formed.
When asked how water appeared on Earth, adherents of this hypothesis answer that the first molecules of this liquid were brought with them by meteorites. At first, these molecules existed in the form of gas and accumulated, and later, when the planet began to cool, the water turned into a liquid state and formed the Earth's hydrosphere.
It is possible that the chemical formation of water occurred from primary hydrogen protons and oxygen anions, but the likelihood of such a reaction occurring in the thickness of celestial bodies that subsequently fell to Earth is catastrophically small.
Another hypothesis about how water appeared on Earth
It was proposed by a group of researchers led by the famous scientist V.S. Safronov. The essence of his assumption lies in the terrestrial origin of the water that formed in the bowels of the planet.
Under the influence of numerous meteorite falls, our then-hot planet began to form a large number of volcanoes, from which magma erupted. Along with it, “water vapor” was released to the surface, which became the reason for the formation of the Earth’s hydrosphere.
Despite the fact that the theory is based on the terrestrial origin of water, it cannot answer many questions. For example, how did the rocks in the lithosphere melt so much as to cause the formation of many volcanoes? And how did water vapor form? At first, scientists assumed that at that time there was groundwater, which escaped in a gaseous state through volcanic vents along with magma.
This theory of steam formation was refuted by P. Perrault, a naturalist of the 17th century. He proved that groundwater was formed due to precipitation, and this requires the presence of an atmosphere. 4.4 billion years ago there was no atmosphere.
And the last theory
So how did water appear on Earth? Another hypothesis was able to approach the question of the formation of the planet’s hydrosphere from a different angle. Like the previous assumption of V.S. Safronov and his co-authors, this hypothesis is based on the terrestrial origin of water.
The difference is that, according to researchers, water molecules were formed together with the protoplanetary disk of the Earth, i.e. at the moment of the formation of the planet itself. The source of water molecules was deuterium and oxygen.
Deuterium is ordinary hydrogen with one neutron in its nucleus. This heavy isotope was found in samples of ancient basalts discovered in the Arctic on Baffin Island (1985). These rocks are formed from particles of protoplanetary dust that were not exposed during the formation of the planet. According to the researchers, the chemical nature of deuterium would not allow the isotope to form outside the planet.
This is how water appeared on Earth according to these scientists. If their data is correct, about 20% of the modern world ocean was formed during the formation of the protoplanetary disk. Today, researchers are looking for a way to prove that most of the world's oceans, as well as atmospheric water vapor and groundwater, were formed from "protoplanetary" water.
