At the bottom of the oceans, in an environment shrouded in perpetual night and probably Hydrothermal vents are not conducive to life, they are home to rich ecosystems (bacteria, extreme archaea, worms, crustaceans, fish, etc.). It is one of the main pathways as a place where life emerged over 3.5 billion years ago. Hot and charged with many minerals and molecules as it passed through the rocks of the ocean floor, the water from the springs would have fueled prebiotic chemical reactions, the ones that led to the formation of the first organic molecules and the first metabolic reactions.
To understand the origins of life, it is necessary to learn more about the physical and chemical properties of water from primeval springs. But due to the weathering of the rocks, there is no direct evidence of the contents of these springs. Dustin Traill of the University of Rochester in the US and Thomas McCollum of the University of Colorado were able to determine the composition of this primordial soup using very ancient crystals that stand up well to the test of time, zircons.
The eight crystals studied by the researchers come from a very interesting deposit, the Jack Hills deposit, in Australia, of which zircons are the oldest terrestrial minerals ever found, given that some of them are up to 4.4 billion years old. The two scientists studied zircons that formed 3.9 billion years ago at relatively low temperatures, which means that they did not come from the crystallization of magma but from recrystallization in hot watery liquids diffused at depth. By analyzing the composition of these zircons, it is thus possible to determine the composition of the fluids in which they appeared. The researchers also synthesized the zircons in the laboratory under different conditions to compare the compositions of natural and synthetic zircons.
For example, Dustin Trail and Thomas McCollom analyzed the composition of cerium (Ce) which mainly exists in two forms,3 + and this is4+. The relative abundance is related to the degree of fluid oxidation: the more oxidized the fluid, the higher the Si4+ compared to this3 +. gold in m4+ Zircon crystals fit more easily than Ce3 +. Thus, if the zircon is enriched with cerium, it means that there was comparatively more Ce4+ Therefore the liquid is oxidized to some extent.
This is exactly what Dustin Traill and Thomas McCollum observed: The fluids that interacted with these zircons were more oxidized than the Earth’s mantle in which they circulated. In addition, these fluids were three times less rich in chlorine than the present-day oceans: so they were certainly fresh water from surface sedimentation, which after passing through the rock would have risen to form a hydrothermal source. This hypothesis is supported by oxygen isotope analysis of zircons, which show the same signature as current hydrothermal freshwater vents (such as those in Yellowstone Park, in the United States).
Thanks to numerical models using their experimental data, the researchers were able to prove that these fluids were compatible with the emergence of life. They contained, among other things, large amounts of methane (which can be involved in the synthesis of nucleic and amino acids), and large amounts of zinc (which promotes the polymerization of small organic molecules by allowing them to stick to metal surfaces). They are also marked with an admixture of iron in the form of Fe3 + and Fe2 +which would be conducive to the production of amino acids.
These fluids may have represented only a small part of the great diversity of hydrothermal environments in the early Earth, but they are the oldest that have ever been successfully described. This new method can be applied to Martian zircons to determine if the Red Planet experienced the conditions necessary for the emergence of life as we know it.
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