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Fallen near the eponymous village in 1864, this meteorite has not finished revealing its secrets brought from space, including the presence of essential building blocks of life that may very well have been brought to Earth by other meteorites, long before the appearance of life.
This new clue that a "starter molecular kit" for the chemistry of life could come from space was published in Nature Communications.
© Collection of MNHN-Paris
For decades, scientists have been tracking in meteorites the chemical ingredients that may have contributed to the emergence of life on Earth. Primitive meteorites did indeed widely seed the Earth very early in its history, mainly during a period called the Late Heavy Bombardment, about 4.1 to 3.8 billion years ago.
While amino acids, the basic building blocks of proteins, and nucleic acids, those of DNA, are regularly identified on meteorites, sugars, although essential to life molecules like RNA, remained surprisingly rare and difficult to detect. This absence contrasted with experiments conducted in the laboratory under conditions simulating space, in which complex sugars easily form in the presence of the basic organic molecules cataloged in space.
Searching for new clues, scientists from the Institut de chimie de Nice (CNRS/Université Côte d'Azur) conducted very thorough analyses with advanced techniques on a fragment of the Orgueil meteorite. This fragment of very ancient space rock formed at the beginning of the solar system about 4.5 billion years ago; this carbonaceous chondrite fell near the eponymous village in southern France in 1864.
Thanks to a particularly fine analytical method, and especially a very gentle extraction of the organic molecules present in the analyzed fragments, the team managed to identify several five-carbon sugars including ribose, a key component of RNA, but also arabinose, xylose, lyxose, and ribulose.
These sugars could obviously have resulted from contamination of the meteorite since its arrival on Earth. But the analyses rule out this hypothesis. Indeed, these sugars are chiral molecules, which, in the living world, exist only in one of the two forms or enantiomers. However, some of the identified sugars exhibit a so-called "racemic" distribution, meaning a balanced mixture of two mirror forms of the molecule, characteristic of a non-biological and therefore very likely spatial origin.
The study also suggests that these sugars would be much more abundant than they appear. The very gentle extraction methods implemented here to preserve the most fragile molecules like sugars as much as possible strongly underestimate their actual quantity in the meteorite, where they interact strongly with the minerals that compose it. Once these biases are taken into account, the concentrations of some sugars appear comparable to those of amino acids present in the same samples!
By comparing the sugars to the amino acids detected simultaneously in the sample, the scientists reinforce the idea of a common extraterrestrial origin. All the results suggest that meteorites could have brought to the early Earth a truly diverse "starter kit" of prebiotic organic molecules. This study published in Nature Communications provides new clues to the greatest mystery concerning our Earth: the appearance of life.
Author: Anne-Valerie FOILLARD RUZETTE