A group of scientists at NASA’s Ames Research Center created uracil, cytosine and thymine, three nucleobases that are among the chemical components of RNA and DNA. This result was obtained by reproducing the conditions existing in the space, even interstellar. Obtaining these molecules by non-biological processes shows that at least part of life’s building blocks may have arrived on Earth after being formed in space.
To create the three nucleobases, NASA scientists started from pyrimidine, a molecule composed of hydrogen, carbon and nitrogen. It was found in meteors so there’s the certainty that it exists in space. Uracil, cytosine and thymine are derived from pyrimidine and the experiment aimed to verify that it was possible to obtain them under the conditions found in space.
For years, NASA scientists have been simulating the conditions existing in interstellar space or in the outer solar system in laboratory for various researches. In this case, they exploited this possibility to check how pyrimidine molecules react. The nitrogen atoms in their molecules make them less stable so the researchers wanted to verify if they can survive and can undergo reactions that turn them into more complex molecules.
The researchers thought that in theory the pyrimidine molecules could survive long enough to reach clouds of interstellar dust. At that point, they would find protection there and most of them would freeze, a very stable environment.
This hypothesis was tested in the Ames Astrochemistry Laboratory, where scientists exposed a sample of ice containing pyrimidine to conditions that replicate those in space. They’re high vacuum, extremely low temperatures around -262° Celsius (about -440° Fahrenheit) and a strong presence of ultraviolet radiation.
The result is that the pyrimidine frozen in ice composed mainly of water but also ammonia, methanol or methane is much less vulnerable than if it were present in gaseous form in open space. The consequence is that instead of being destroyed, many molecules were transformed becoming more complex in the form of uracil, cytosine and thymine.
Specifically, the photons that bombarded the sample broke the chemical bonds in the ice and fragments of molecules are recombined to form the nucleobases. Such reactions may be an important link between what happens in space and what reached Earth early in its history to create the first life forms.
Uracil, cytosine and thymine are just three of the components of RNA and DNA and there are still many things to understand in order to say that we have completely solved the mystery of the birth of life on Earth. However, it’s a step forward in this research and shows how at least some of the “seeds” of life can be created in space.