About a half of the amino acids used in proteins, i.e. ten of them, can form easily in abiotic conditions and they are widespread in some celestial bodies.

They are easily distinguished from terrestrial contaminants, because they are a mixture of left-handed and right-handed isomers.

When analyzing the genetic code in order to determine which amino acids have already been used in the earlier versions of the genetic code and which have been added more recently, the same simpler amino acids that are easy to synthesize even in the absence of life are also those that appear to have been the only amino acids used earlier.

The article contains the phrase "Given the fact that the current scenario is that life on Earth started with RNA".

This is a fact that it is too often repeated like if it were true, when in reality one of the few things that can be said with certainty about the origin of life is that it has not started with RNA.

What must be true is only that RNA had existed a very long time before DNA and DNA has been an innovation that has been the result of a long evolution of already existing life forms, long before the last ancestor of all living beings that still exist now on Earth.

On the other hand, proteins, or more correctly said peptides, must have existed before any RNA. Moreover, ATP must have existed long before any RNA.

RNA has two main functions based on its information-storage property: the replication of RNA using a template of RNA (which was the single form of nucleic acid replication before the existence of DNA) and the synthesis of proteins using RNA as a template.

Both processes require complex molecular machines, so it is impossible for both of them to have appeared simultaneously. One process must have appeared before the other and there can be no doubt that the replication of RNA must have appeared before the synthesis of proteins.

Had synthesis of proteins appeared first, it would have been instantly lost at the death of the host living being, because the RNA able to be used as a template for proteins could not have been replicated, therefore it could not have been transmitted to descendants.

So in the beginning RNA must have been only a molecule with the ability of self replication. All its other functions have evolved in living beings where abundant RNA existed, being produced by self replication.

The RNA replication process requires energy and monomers, in the form of ATP together with the other 3 phosphorylated nucleotides. Therefore all 4 nucleotides and their phosphorylated forms like ATP must have existed before RNA.

ATP must have been used long before RNA, like today, as a means of extracting water from organic molecules, causing the condensations of monomers like amino acids into polymers like peptides.

The chemical reactions in the early living forms were certainly regulated much less well than in the present living beings, so many secondary undesirable reactions must have happened concurrently with the useful chemical reactions.

So the existence of abundant ATP and other phosphorylated nucleotides must have had as a consequence the initially undesirable polymerization and co-polymerization of the nucleotides, forming random RNA molecules, until by chance a self-replicating RNA molecule was produced.

Because the first self-replicating RNA molecule did not perform any useful function for the host life form, but it diverted useful nucleotides from its metabolism, this first self-replicating RNA molecule must be considered as the first virus. Only much later, after these early viruses have evolved the ability to synthesize proteins, some of them must have become integrated with their hosts, becoming their genome.

The catalytic functions that are now performed mostly by proteins, i.e. amino acid polymers that are synthesized using an RNA template, must have been performed earlier by peptides, i.e. typically shorter amino acid polymers that are synthesized without the use of RNA templates.

Even today, all living beings contain many non-ribosomal peptides, which are made without RNA, using processes that are much less understood than those that involve nucleic acids.

The difference between a living being that would be able to make only non-ribosomal peptides and one that makes proteins using RNA templates is pretty much the same difference as between a CPU with hard-wired control and a CPU with micro-programmed control, with the same advantages and disadvantages.

Life forms able to reproduce themselves must have existed before the appearance of the nucleic acids, but they must have been incapable of significant evolution, because any random change in the structure of the molecules that composed them would have been very likely to result in a defective organism that would have died without descendants. This is similar with a hard-wired control, where small random changes in the circuits are unlikely to result in a functional device.

On the other hand, once the structure of the enzymes was written in molecules of nucleic acids, the random copying errors could result in structures very different from the original structures, which could not have been obtained by gradual changes in the original structures without passing through non functional structures that could not have been inherited.

So the use of molecules that can store the structural information of a living being has enabled the evolution towards much more complex life forms, but it cannot have had any role in the apparition of the first life forms, because the replication of any such molecule requires energy that can be provided only by an already existing life form.