How life originated on Earth is one of science’s most enduring mysteries. However, there is growing evidence to suggest that the building blocks may have been delivered to us from space. A new study makes this scenario even more likely. Researchers have indeed identified in meteorites the last two DNA nucleobases that were missing until now.
The origin of life
Recent sample return missions from the Ryugu (C-type) asteroids and Determining (type B) led by JAXA (Japanese agency) and NASA will provide us with important information on the evolution of extraterrestrial organic molecules and potential clues regarding the origins of life on Earth through chemical analyzes of pristine materials not not been compromised by terrestrial contamination.
The scientific rationale for choosing C- and B-type asteroids for sample-return missions is that these carbon-rich asteroids are plausible parent bodies of carbonaceous chondrites in which various sequences of primordial organic molecules of astrochemical interest, including amino acids and sugarswere detected.
From nucleobases, one of the structural components of nucleic acids, have also been identified in carbonaceous chondrites. DNA and RNA are made up of five of these nucleobases: adenine, cytosine, guanine, thymine and uracil. Adenine, guanine and uracil have all been previously discovered in meteorite fragments. A team announces that it now has identified the other two (cytosine and thymine) for the first time.
All basic ingredients came from outer space
According to the research team, the fact that these two nucleobases have escaped detection so far could be explained by a structure plus fragile than the others. Normally, scientists wanting to examine compounds in a meteorite sample place the grains in hot formic acid. They then analyze the molecules in the resulting solution. However, this process can destroy some compounds.
For this new work, the researchers opted for a cold infusion. Combined with state-of-the-art analytical instruments more sensitive that before, this gentler process finally allowed the detection of fragile cytosine and thymine.
Although all of the ingredients needed to make DNA and RNA may have been present in ancient asteroids and comets, the authors point out that it is unlikely that more complex polymers could have formed directly in the planet. ‘space. In contrast, the study again supports the idea that a diverse suite of exogenous meteoric organic matter, including nucleobases, may have been delivered to the primitive Earth. This process could have taken place during the last period of intense bombardment, there is about 4–3.8 billion years old.
Thus more than ever, the influx of these extraterrestrial organic materials is today considered to have played an important role in the chemical evolution of the primordial stage of the Earth.
Details of the study are published in Nature Communications.