Reacción a "Reactions: New fossils from eukaryotes found in millions-of-years-old rocks "

Sterols are a type of molecule found in the membranes of various living beings, especially eukaryotes. These molecules are quite stable, so they can be found in the sediments of the fossil record and are therefore known as 'biomarkers' or 'molecular fossils'. Obviously, molecules are going to be affected by diagenesis (the processes that form sedimentary rocks). For example, due to diagenesis, cholesterol is modified to cholestane. If cholestane is present in a sediment, that indicates that modern eukaryotes were present when it formed. Knowing that, you can make a correlation between the type of biomarker found in a geological sample and the type of organisms that might have existed at that time. But there are a couple of problems. The first is that the more time passes, the more the biomarkers degrade and alter, so the correlation becomes less and less accurate. The other is that, even if we know the original molecule, if we don't know how it is modified, we cannot identify the biomarker that is produced.  

Knowing how these molecular alterations and molecules are produced can allow us to identify new biomarkers. That is precisely what the authors of this study have done. The researchers have found a new type of eukaryotic biomarker, proto-steroids, which until now was not considered as such. These proto-steroids come from molecules such as lanosterol and cycloartenol, which are intermediary molecules of the sterol pathway in today's eukaryotes.   

I think it is a good quality and rigorous study. They have collected samples from different geological periods and analysed them with the most appropriate technology available to determine their composition. In addition, they have been very careful to avoid contamination during the handling of the samples. The results show that proto-steroids are present in rock samples ranging in age from 1.64 billion to 800 million years. Until now, no eukaryotic sterols had been found in samples of these ages. This would indicate that the most abundant eukaryotes at that time were different from today's eukaryotes in terms of sterol synthesis and that substances such as lanosterol and cycloartenol were not intermediates, but end products with a biological function.   

Modern eukaryotes capable of producing molecules such as cholesterol and the like appeared about 1 billion years ago, during the so-called Tonic period. They became the dominant eukaryotes thanks mainly to the proliferation of red algae (rhodophytes) 800 million years ago, coinciding with the increase of oxygen concentration in the atmosphere. From that time onwards, 'molecular fossils' such as cholestane and the like began to be detected.  

As this is a pioneering work, both its methodology and its results will have to be replicated and confirmed by other groups. But the results obtained fit quite well with the results of other work being published recently on the origin and evolution of the eukaryotic cell.