There are theories that claim that we should not exist, or at least suggest that our life today did not seem to be in the initial plans. One of them is the Big Bang, which says that the same amount of matter as antimatter was created at the origin of the universe. When a particle touched its antiparticle, it disintegrated, making it impossible to accumulate atoms that made the world we know possible. A phenomenon still unexplained broke that tie and allowed our existence, but there were still obstacles to overcome before it became a reality. Another fortunate event is the one that covered the Earth with oceans and made it fertile for life. The formation models of the Solar System estimate that water should be scarce on the planets closest to the star, but it is obvious that, at least in ours, this is not the case.
In attempts to explain this happy anomaly, the scientific study suggests that 3.9 billion years ago, the Earth suffered an intense bombardment from asteroids and comets that brought with them water and organic elements that, only 400 million years later, allowed that life appeared. To accommodate the formation theories of our planetary system, it was proposed that meteorites, known as carbonaceous chondrites, came from the outer borders of the solar system, where the heat from the star would not have volatilized the water as in the interior regions. Now, a work published in the journal Science , points to another type of asteroid as the source of the liquid compound essential for life that we know.
The hypothesis that distant comets and meteorites filled the Earth with water requires a complex process of gravitational influences between the giant planets and those celestial bodies to bring them here from their distant orbits. Laurette Piani and a team from the National Center for Scientific Research (CNRS, from its French acronym) and the University of Lorraine (France), have tried to justify another of the possibilities that had been proposed to explain that this is the blue planet.
The Earth was formed from the amalgamation of materials found in the nebula that gave rise to the solar system. "Today we know that terrestrial planets, including Earth, do not form suddenly, but with the aggregation of hundreds of bodies," explains Josep Maria Trigo, principal investigator of the group of minor bodies and meteorites at the Institute of Space Sciences (CSIC -IEEC), in Barcelona. "The bodies that formed the Earth would be formed at a shorter distance from the sun and 80 or 90% would be enstatite chondrites [the most abundant mineral in them] or ordinary", he adds.
In principle, due to its formation close to the Sun, it was thought that in those fundamental bricks with which the Earth was built there would not be enough water to explain its abundance on our planet. However, analysis by Piani and his colleagues suggests that in these early rocks there was enough hydrogen to bring up to three times the mass of water that the oceans contain today. To make this robust claim, the researchers accurately measured the concentrations and ratios of hydrogen and deuterium (a version of hydrogen with a neutron accompanying the proton) in thirteen meteorites from enstatite asteroids. In addition to checking that they had sufficient amounts of hydrogen, they observed that the amounts of hydrogen and nitrogen isotopes coincide with those of the Earth's mantle.
The authors acknowledge that they cannot calculate when the arrival of these asteroids carrying the elements necessary for the appearance of terrestrial water took place, but they estimate that it occurred in a sufficiently late period of the formation of the Earth. Jesús Martínez Frías, researcher at the CSIC and director of the Spanish Network of Planetology and Astrobiology, agrees that if the bombing had occurred too soon, before 3,800 million years ago, the water would have evaporated. "The bombardment after the accumulation of the first planetesimals would have destroyed the primitive crust and the water vapor and other gases escaped and remained forming the atmosphere and the water of the Earth," he says. "This also mixed with other fluids from the subsoil through volcanism and all these volatile emissions enriched that primitive atmosphere," he adds.
The fact that most of the terrestrial water comes from these chondrites in the region of the Solar System near the Earth does not rule out the role that those that arrived from the colder and more distant zones could fulfill. "The enstatitics were important to create habitable conditions by bringing water, but the carbonaceous, which have amino acids, ureas, purines, are more important to make the origin of life possible," he explains. Trigo, who considers the work published today by Science to be very relevant , points out that this may mean that “carbonaceous chondrites would have contributed a smaller but significant amount, around 5 to 10%, of that water and nitrogen [from Earth] , although they could have done it later, as a result of continuous collisions with other objects throughout the history of the Earth ”.
To better understand this critical stage in the history of the planet, it will be necessary to travel to asteroids where to take samples with which to make even more precise measurements than that of the Piani team. As Frías explains, when it is possible to visit asteroids with some regularity, each type will have its interest: “Metallic asteroids are more interesting to search for mineral resources such as rare earths, those that give rise to carbonaceous chondrites are interesting from the point of view of origin of life and the enstatitics to explain how the Earth began to be habitable ".
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