All of Life’s Nucleic Acids May Have Extraterrestrial Origins
All 5 nucleobases of RNA and DNA have been found in meteorites for the first time. These chemicals are necessary ingredients for life on Earth and numerous purines and also two pyrimidines– thymine and cytosine– not previously spotted in meteorites were discovered.
The discoveries originate from analyzing three carbonaceous meteorites, known to be abundant in organic molecules. The discovery ‘provides added support for the theory that the delivery of these compounds to Earth by meteorites might have contributed to the appearance of genetic functions for very early life, according to astrobiologist Daniel Glavin at Nasa, which gave one of the meteorites.
Previously, 7 purine bases and one pyrimidine base had actually been discovered in meteorites. Experiments had depended on a hot formic acid extraction method to release the nucleobases from meteorite powders. This ‘might have brought about the destruction of some nucleobases,’ suggests Glavin.
The group based in Japan utilized a milder extraction method and a new high-resolution mass spectroscopy technique to measure nucleobases down to parts per trillion. Liquid chromatography was additionally used to identify structural isomers of nucleobases.
‘ The detection of cytosine is very surprising because it has actually been regarded as really weak against aqueous processes possibly experienced on the meteorite parent body,’ remarks Yasuhiro Oba, an astrochemist at Hokkaido University in Japan, that did the sample analyses.
Extraterrestrial nucleobases
These building blocks of DNA and RNA were taken out from 3 meteorites: Murchison, probably the most popular meteorite for researching extraterrestrial organic molecules, which fell in 1969 in Australia; the Murray meteorite, which blew up at high altitude in 1950 and came down east of Murray, Kentucky; and the Tagish Lake meteorite, a big object that struck a frozen lake in Canada in 2000.
Comparable concentrations of nucleobases in these meteorites ‘were also synthesized in laboratory experiments mimicking photochemical reactions in the interstellar medium, offering additional evidence that nucleobases can be formed in space,’ says Glavin.
Chemist Uwe Meierhenrich at the University of Nice Sophia Antipolis in France comments that ‘this finding confirms that the molecular selection included in the origins of life occurred on Earth, and not before.’ He includes that ‘this further validates our models on the molecular origins of life on Earth, as the very same hypothesis seems valid for amino acids.’ Over 90 amino acids have actually been located in meteorites, while biological organisms employ 21 of them, implying that there was extraterrestrial delivery of a broad range of organic molecules.
Based upon laboratory experiments and models, some astrobiologists propose that the composition of early Earth’s atmosphere was too oxidizing to form nucleobases by natural processes easily, notes Glavin. ‘Therefore, meteorite delivery of nucleobases to the Earth would have supplied a source of nucleobases for the development of life.’
Is the theory bullet-proof?
Not everyone is convinced. ‘The paper did not offer sufficient evidence to firmly establish that cytosine, uracil, and thymine were extraterrestrial in the beginning,’ comments Michael Callahan, an analytical chemist at Boise State University, Idaho. He adds that terrestrial soil can have higher concentrations of cytosine, uracil, and thymine, so it is hard to figure out how much is extraterrestrial versus terrestrial.
Likewise, the pyrimidines existed at exceptionally low concentrations. ‘If these results are representative of common pyrimidine concentrations in meteorites after that geochemical synthesis on early Earth would likely have been in charge of the appearance of genetic material instead of inputs from extraterrestrial delivery,’ Callahan states.
Read the original article on Royal Society of Chemistry.
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