How did the building blocks of life reach Earth? Zinc fingerprints in meteorites provide clues

An iron meteorite from the core of a molten planetesimal (left) and a chondrite meteorite from a “primitive” unmolten planetesimal (right). Credit: Rayssa Martins/Ross Findlay
Researchers used the chemical fingerprint of zinc in meteorites to determine the origin of volatile elements on Earth. The results suggest that without the “unmolten” asteroids, there may not have been enough of these compounds for life to emerge on Earth.
Volatile substances are elements or compounds that change to vapor at relatively low temperatures. These include the six most common elements found in living things, as well as water. Zinc in meteorites has a unique composition and can be used to determine the source of Earth’s volatiles.
Researchers from the University of Cambridge and Imperial College London have previously discovered that Earth’s zinc comes from different parts of the solar system, with about half coming from beyond Jupiter and the other half. comes from a place close to the earth.
“One of the most fundamental questions about the origin of life is where did the materials needed for life to evolve come from?” says Dr Leissa Martins from the University of Cambridge’s School of Earth Sciences. “Understanding how these materials originated on Earth may provide clues to how life originated on Earth and how it may emerge elsewhere. ”
Planetesimals are the main constituents of rocky planets such as Earth. These small objects form through a process called accretion, where particles around a young star begin to stick together and gradually form larger objects.
However, not all planetesimals are created equal. The earliest planetesimals to form in the solar system were exposed to high levels of radiation, which caused them to melt and lose volatile materials. However, some of the planetesimals that formed after these radioactive sources were mostly extinct helped them survive the melting process and store more volatile materials.


An iron meteorite from the core of a molten planetesimal (left) and a chondrite meteorite from a “primitive” unmolten planetesimal (right). Credit: Sedgwick Museum of Earth Science, University of Cambridge.
In a study published in the journal Science Advances, Martins and colleagues looked at the different forms of zinc that reached Earth from these planetesimals.
The researchers measured zinc in a large sample of meteorites originating from various planetesimals and used this data to track the entire period of Earth’s accretion, which took tens of millions of years. modeled how they obtained their zinc.
Their results show that while these “molten” planetesimals make up about 70% of Earth’s total mass, they only provide about 10% of the zinc.
According to this model, the remaining zinc on Earth comes from materials that did not melt and lose their volatile elements. Their findings suggest that undissolved, or “primitive” materials are an essential source of volatile substances for Earth.
“We know that the distance between a planet and its star is a determining factor in establishing the conditions necessary for that planet to maintain liquid water on its surface,” the study said. said lead author Martins. “However, our findings show that regardless of their physical state, there is no guarantee that a planet has incorporated the right materials to hold sufficient amounts of water and other volatile materials in the first place. It shows.”
The ability to track elements through millions or even billions of years of evolution could be an important tool in the search for life elsewhere, such as Mars or planets beyond our solar system.
“Similar situations and processes are likely to occur in other young planetary systems,” Martins said. “The role these different materials play in providing volatiles is something to keep in mind when looking for habitable planets elsewhere.”
Further information: Rayssa Martins et al, Proto-asteroids as a major source of volatiles on Earth, Science Advances (2024). DOI: 10.1126/sciadv.ado4121. www.science.org/doi/10.1126/sciadv.ado4121
Provided by University of Cambridge
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