Water present before the formation of the Earth
A team of researchers from the Institute of Materials Physics, Mineralogy and Cosmochemistry of the University of Paris-Saclay and the University of Pau and the Pays de l’Adour have studied the hydrogen isotopic composition of minerals present in certain meteorites to gain a better understanding of the origin of water on Earth and in particular to know which hydrogen isotopes were present at the time of the formation of the solar system.
The primitive meteorites studied, called chondrites, provide information on the original composition of the solar system and have revealed that water was present before the formation of the solar system and, therefore, before the Earth’s shape. The study investigates the isotopic composition of the two elements, hydrogen and oxygen, which make up water.
Concerning hydrogen, it is the presence of three of these isotopes, protium, deuterium and tritium, which interests the researchers more precisely. In particular, deuterium and its ratio to protium, the isotope most present on Earth. The difficulty in measuring the isotopic composition of hydrogen lies in the chemical alterations that the meteorites underwent after their accretion phase, after gaining volume, because these alterations can mask the primary piece before the solar system’s formation.
The researchers, therefore, chose the meteorites that had undergone minor alteration and then analyzed them using a method specific to this study.
The results were published in Nature Astronomy and show that the first minerals formed on these chondrites by condensation from the solar nebula. For these primary minerals, the ratio between protium and deuterium is meager, indicating that they were formed in conditions present in a gas cloud enriched with water vapour before the constitution of the solar system, contrary to secondary minerals which present a ratio close to that of terrestrial oceans.
The analysis shows that two gas reservoirs were present at the time of the first phase of formation of the solar system, estimated at 200,000 years, one from a solar nebula and the other from a protoplanetary nebula strongly enriched in water.
The various telluric planets of the solar system were then formed progressively by using the protoplanetary chemical reservoir before their formation. This reservoir would have been formed from interstellar water-rich materials, which would have flowed towards the center of the solar system.
The differences in the isotopic composition of the meteorites are explained by the various phases of formation, initially at the level of the center of the protoplanetary disc and then by migrating towards the planetary gas reservoir.
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