For years, astronomers have never ceased to be surprised by discovering the basic elements of life throughout the Universe, from the distant, cold molecular clouds that give rise to stars to the rings of matter that surround newborn suns. But how did those arrive? ‘bricks’ of life to Earth?
To answer the question, a team of scientists from the University of Cambridge and Imperial College London has used the chemical signatures of zinc contained in meteorites to determine the origin of the volatile elements on our planet. The results suggest that without the ‘non-melted’ asteroids there would most likely not have been enough of these compounds on Earth for life to arise.
Volatiles are elements or compounds that turn into vapor at relatively low temperatures. And that includes the six most common elements in living organisms, in addition to water. The researchers chose zinc from meteorites because it has a unique composition, which can be used to identify the sources of terrestrial volatiles.
«One of the fundamental questions about the origin of life – says Rayssa Martins, lead author of the study – is where the materials needed for it to evolve come from. “If we can understand how these materials came to exist on Earth, we might have clues about how life originated here and how it might arise elsewhere.”
Written on planetesimals
The main ‘pieces’ of which rocky planets like Earth are made up are the so-called ‘planetesimals’, small bodies that are formed by accretion, a process in which particles around a young star begin to join together to progressively form rocks. bigger.
But not all planetesimals are the same. The first ones that formed in the Solar System, in fact, were exposed to high levels of radioactivity, which caused them to melt and therefore lose practically all of their volatiles. But some planetesimals formed later, when radioactivity had already ceased, allowing them to survive the fusion process and, more importantly for us, to retain their volatile elements.
In a study recently published in ‘Science Advances‘, Martins and his colleagues looked at the different forms of zinc that reached Earth from these planetesimals. To do this, they measured the amounts of zinc in a large sample of meteorites, and used the data to make a model that reflects the way in which the Earth obtained its zinc. Researchers traced the entire period of accretion of our planet, a process that lasted several tens of millions of years.
The origin of volatile elements
The results show that while these ‘molten’ planetesimals contributed about 70% of Earth’s total mass, they only provided about 10% of its zinc.
According to the model, therefore, the rest of the zinc on Earth came from materials that did not melt or lose their volatile elements. These findings suggest that unmelted materials were an essential source of volatiles for the planet.
“We know that the distance between a planet and its star is a determining factor when establishing the necessary conditions for that planet to maintain liquid water on its surface,” says Martins. “But our results show that there is no guarantee that planets will incorporate the materials necessary to have enough water and other volatiles from the beginning, regardless of their physical state.”
Therefore, the ability to trace elements over millions or even billions of years of evolution promises to be an essential tool in the search for life on other worlds, such as Mars or planets outside our Solar System.
«It is likely – concludes Martins – that similar conditions and processes also occur in other young planetary systems. “The role these different materials play in supplying volatiles is something we need to take into account when looking for habitable planets.”
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