For the very first time, Japanese researchers have identified the five nitrogenous bases that form the basis of our genome in meteorites that have fallen to Earth. A discovery that makes this scenario on the origin of life even more tangible.
It has been a long time since biologists and astronomers believe that meteorites could have provided the first bricks from which life was built on Earth. The indisputable evidence in favor of this theory, on the other hand, is still conspicuous by its absence; or at least that was the case until the publication of work by researchers from Hokkaido University, Japan, who detected the five “fundamental bricks” of life in a space rock.
Life as we know it on Earth relies heavily on DNA. Under its simplistic looks, it is a biochemical support of great power; it is thanks to it that living beings are able to preserve the integrity of their genetic heritage.
This genetic information is coded thanks to a succession of nitrogen bases which could be described as “fundamental bricks” of our genome; in DNA, these are adenine, thymine, cytosine, and guanine, which are more often denoted by the letters A, T, C, and G. It is the same in RNA, but with one exception. In this case, thymine (T) is replaced there by another nitrogenous base, uracil (U).
These units are divided into two categories: A and G are what are called purineswhile T, C and U belong to the class of pyrimidines. In this context, it is useless to dwell on the biochemical differences between the two classes; what is more important in our case is where they are found.
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Indeed, since this hypothesis emerged, almost all meteorites have been scrutinized as soon as they are discovered; astrochemists thus hope to find these famous bases there, which would constitute a strong argument in favor of this theory. So far, they have already spotted purines (A and T) there; on the other hand, the pyrimidines were still conspicuous by their absence.
A particularly curious discrepancy that still leaves researchers perplexed to this day. Why on earth are purines so predominant, when the two classes should theoretically be able to form under extremely similar conditions? To date, there are several valid theories; the definitive answer, on the other hand, remains inaccessible for the moment.
But while waiting to achieve this, the investigative work continues; recently, researchers from the University of Hokkaido have given the cover with advanced analytical techniques. They used a detection technique originally designed for the pharmaceutical industry, which uses it to detect minute traces of certain compounds.
This method made it possible to analyze meteorites with an accuracy “10 to 100 times” superior to that offered by previous tools, explain the researchers. This is how they were able to detect not only the two purinesbut also the three pyrimidines in the same meteorites. The concentration was certainly extremely weak, but that remains the very first time that someone detects all of this cocktail of molecules in the same extraterrestrial substrate.
A strong argument in favor of this track
An observation with serious consequences; it considerably reinforces the idea that meteorites could have contributed to the emergence of the first genetic mechanisms from which life developed. Moreover, this scenario is also interesting, because it is compatible with some of the most promising leads on the emergence of life.
For example, we can cite the famous hypothesis called “of the World at RNA”, which you recently told us about in this article; it stipulates that the first forms of terrestrial life would have developed from RNA, and this work precisely shows that this material could have arrived on Earth via a meteorite.
Obviously, this is not no formal proof yet; these elements alone still remain insufficient to rule out all other scenarios, like that of a spontaneous appearance on Earth. On the other hand, it is undoubtedly a new element in favor of this very promising track. With a bit of luck, many other works already in progress will soon allow us to see things more clearly.
For example, we can cite those that NASA is carrying out with Perseverance and Ingenuity; the rover is currently searching an ancient, dry Martian delta, hoping to find old biosignatures there. Day after day, we are therefore gradually getting closer to an answer to this question which has been plaguing researchers for decades.
The text of the study is available here.