2024-10-11 18:16:00
For years, astronomers have been amazed by discovering the fundamental 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 these “building blocks” of life reach Earth?
To answer the question, a team of scientists from the University of Cambridge and Imperial College London used the chemical signatures of zinc in meteorites to determine the origin of volatile elements on our planet. The findings suggest that without the “unfused” 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 this includes the six most common elements in living organisms, as well as water. The researchers chose zinc from meteorites because it has a unique composition, which can be used to identify sources of terrestrial volatiles.
«One of the fundamental questions about the origin of life – explains Rayssa Martins, lead author of the study – is where the materials necessary for its evolution come from. “If we can understand how these materials came to exist on Earth, we may have clues about how life originated here and how it might form elsewhere.”
Written on planetesimals
The main ‘pieces’ that make up rocky planets like Earth are so-called ‘planetesimals’, small bodies that form through accretion, a process in which particles around a young star begin to come together to form progressively larger rocks .
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 led them to melt and therefore to lose practically all their volatile substances. But some planetesimals formed later, when the 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 ‘Advances in science‘, Martins and his colleagues examined the different forms of zinc that reached Earth from these planetesimals. To do this, they measured the amount of zinc in a large sample of meteorites and used the data to create a model that reflected how Earth obtained its zinc. The researchers traced the entire period of our planet’s accretion, a process that lasted several tens of millions of years.
The origin of volatile elements
The results show that although these “melted” planetesimals contributed about 70% of Earth’s total mass, they only provided about 10% of its zinc.
According to the model, then, the rest of the zinc on Earth came from materials that neither melted nor lost their volatile elements. These findings suggest that the 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 conditions necessary 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 needed to have enough water and other volatiles from the start, regardless of their physical state.”
Therefore, the ability to track 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 probable – concludes Martins – that similar conditions and processes also occur in other young planetary systems. “The role that these different materials play in providing volatiles is something we need to take into account when looking for habitable planets.”
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