The isotopic properties of the compound can be used to study its origin and evolution, and we can apply this technique to study the origin of water on Earth. So what do we know about the water on our planet? First of all, there is no other place except Earth. in the solar system OR beyond that we know for sure that it contains liquid water.
We know that there is snow made of water on the Moon and on Europa and Enceladus (the moons of Jupiter and Saturn, respectively), or on comets like 67P/Churyamov-Gerasimenko. We also know of the presence of water vapor in the frigid volcanoes of these moons and in the interstellar medium, especially near regions where stars are forming. So are all these waters the same? Do they have the same isotopic composition?
It so happens that there is a paradox in the origin of water on earth. The environment in which the Sun and Earth originated was quite dry, even though water is one of the most abundant compounds in the star-forming regions where the Sun and Earth evolved. In fact, according to scientific models, rocky planets like Earth appeared in a region of the Solar System close to the Sun. Here, the high temperature prevented the formation of a type of atmosphere where water could evolve beyond the gaseous state. In this way, the formation of water escaped the gravitational pull of the planet.
The presence of carbon, the other basis of life on Earth, also contains a paradox. Carbon is the fourth most abundant element in the universe after hydrogen, helium, and oxygen and the second most abundant element in our bodies (about 20% of our body mass is carbon). However, carbon is ten times less abundant on Earth than in the universe as a whole.
However, what is the importance of carbon here?
Well, a small part (about 5%) of the meteorites that reach our planet today have a high carbon content. They are called carbonaceous chondrites, and interestingly, they also contain significant amounts of water. This means that it must have formed in regions far from the sun, beyond what is known as the ‘frost line’, where temperatures were already well below what, in the early solar system, allowed the formation of ice from water, methane or ammonia. . This is one of the reasons why water is supposed to have reached Earth by bombarding these meteorites during a period when Earth had already cooled since its formation.
In fact, another question is when the water arrived. There is evidence that it existed on our planet 4.4 billion years ago, just over 100 million years after its formation, when our planet’s surface temperature was low enough for water to freeze. This evidence is based on the study of certain minerals such as zircon, which withstands geological changes and the work of the atmosphere well, giving us information about the origins but not so much about the evolution of water on Earth.
Studying the “isotopic abundance” of water in carbonaceous chondrites, at least in those as old as the solar system itself, yields results very similar to those of water on Earth. In particular, the amount of deuterium versus protium is often studied, since the ratio of these isotopes to Earth’s water is quite similar for chondrites near Jupiter, some from the asteroid Vesta. Farther out (for example, in comets in the outer reaches of the solar system), the abundance of deuterium is much greater, occurring in what is known as the Oort cloud.
So what do Jupiter and the Moon have to do with the whole story of water on Earth? In the case of Jupiter, its effect on matter comes from its strong gravitational influence on the solar system, which moves the orbits of many asteroids. Some evolutionary models suggest that at some point in the solar system’s history, Jupiter may not have had the same orbit it does today; instead, it may have been closer to the sun before migrating toward its current position. This Jupiter trip would have had to sweep up objects along the way, which in turn could have been thrown en masse into inner orbits closer to the Sun, thus reaching Earth. This is known as the “late bombardment,” evidenced, for example, by the concentration of meteorite impacts on the Moon about 3.9 billion years ago.
This is where the role of the moon comes into play. To understand this, we must go back to the study of isotopes, but this time we are talking about molybdenum, which is a very rare element. Molybdenum is a metal with 42 protons (by comparison, iron has 26) and dozens of isotopes. It turns out that the relative abundance of these isotopes on Earth is in the middle of the observed abundances of carbonaceous chondrites and chondrites from the distant reaches of the Solar System.
Bearing in mind that molybdenum is denser than iron (a small one-centimeter cube of metal weighs 10 grams, versus seven grams if it were iron and one gram if it were water), and that most of the iron on our planet it is intrinsic, it would not be surprising The belief that the molybdenum that came to earth at the beginning of its history has sunk into the heart of the earth. The surface molybdenum, in the crust or upper mantle, could have a more recent origin, and its isotopic composition indicates regions where there is a lot of carbon and water. The moment links the arrival of molybdenum and water with the effect of Theia, the protoplanet that caused the formation of the Moon after it collided with Earth 4.5 billion years ago, mixing much of its material with the Earth’s mantle. According to these ‘molybdenum studies’, Theia would be a planet that does not come from the region of the rocky planets, but from the region of the gaseous planets (Jupiter, Saturn) and/or icy planets (Uranus, Neptune), which are filled with water .
Therefore, although the evidence is not conclusive, it is possible that the planetary catastrophe caused by Theia, with the consequent formation of the Moon, possibly mediated by Jupiter, had a major influence on the emergence of life for several reasons, among them the representation of most of the water present today on Earth, our planet.
Thus, when we are thirsty, let us consider that our life may be more related to the stars than we think, and that in addition to stardust, we are the product of a struggle of giants.
