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May 3, 2022

Key DNA building blocks found in meteorites supporting the theory that meteorites contributed to origin of life on earth

Filed under: Astronomy / Space,My Thoughts,Science Related — Suramya @ 10:22 AM

How life started on Earth is a subject that is under massive debate and there are multiple theories on how all the required building blocks came into being on earth. One theory is that while the earth was forming and in the early stages of becoming a planet one or more meteorites containing the building blocks of life crashed into the planet. Once the blocks were there over time they combined together to form DNA and then life started.

DNA consists of pairs of molecules called nucleobases which consist of adenine, guanine, cytosine and thymine. These together form the DNA which is the basis of all life on earth. Two of these nucleobases – adenine and guanine were detected in meteorites back in the 1960s. Leading the scientists to postulate that they could have been the source of the compounds on earth. However, till recently no one was able to detect the remaining two DNA nucleobases in any meteorite which made it hard to argue that the meteorites where the source of the nucleobases.

Now, Yasuhiro Oba at Hokkaido University in Japan and his colleagues have discovered the remaining two DNA nucleobases, cytosine and thymine in several meteorites. They examined rocks from three meteorites: the Murchison, Murray and Tagish Lake meteorites that date to about 5 billion years ago and hit earth approximately two decades ago.

The lack of pyrimidine diversity in meteorites remains a mystery since prebiotic chemical models and laboratory experiments have predicted that these compounds can also be produced from chemical precursors found in meteorites. Here we report the detection of nucleobases in three carbonaceous meteorites using state-of-the-art analytical techniques optimized for small-scale quantification of nucleobases down to the range of parts per trillion (ppt). In addition to previously detected purine nucleobases in meteorites such as guanine and adenine, we identify various pyrimidine nucleobases such as cytosine, uracil, and thymine, and their structural isomers such as isocytosine, imidazole-4-carboxylic acid, and 6-methyluracil, respectively. Given the similarity in the molecular distribution of pyrimidines in meteorites and those in photon-processed interstellar ice analogues, some of these derivatives could have been generated by photochemical reactions prevailing in the interstellar medium and later incorporated into asteroids during solar system formation. This study demonstrates that a diversity of meteoritic nucleobases could serve as building blocks of DNA and RNA on the early Earth.

This is an important find but more interestingly the team found that the soil around the Murchison meteorite had a higher concentration of the nucleobases than in the meteorite and according to researchers “If these results are representative of typical pyrimidine concentrations in meteorites, then [nucleobases present on] Earth would likely have been responsible for the emergence of genetic material rather than inputs from extraterrestrial delivery.”

Like always, the more we examine the world the more questions we have. For every question we answer, 10 more are formed. Which is what makes the whole scientific process of discovery so fascinating.

Source: New Scientist: All four of the key DNA building blocks have been found in meteorites
Paper: Identifying the wide diversity of extraterrestrial purine and pyrimidine nucleobases in carbonaceous meteorites

– Suramya

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