Sizes of Genomes of Paleoproterozoic Microfossil Eukaryotes
International journal of paleobiology & paleontology
We studied siliceous rocks (microquartzites) enriched with light isotope 12С of biogenic origin (δ13С up to –29.5‰), found within the volcanogenic-sedimentary strata of the Paleoproterozoic (1640 Ma) of Hogland Island in the Gulf of Finland (Baltic Sea). In these siliceous rocks we found silificated and ferruginizated microfossils of planktonic eukaryotes: amoebas, diatoms,foraminifers, flagellates, virus-like and multicellular organisms. In mineralized cytoplasm and nuclei of microfossils we
... f microfossils we found grains of apatite, which could be crystallized from phosphoric acid residue of decayed nucleotides. This allowed as to estimate the size of genomes of ancient eukaryotes and virus-like structures, which were tens of thousands of times greater than those of genomes of modern single-cell organisms. Additionally, we estimated the weights of genomes of ancient eukaryotes using the principle of genomic-nuclear proportionality: that the molecular weights of genomes are proportional to the size of the nuclei. The weights of genomes of microfossil eukaryotes: flagellates, foraminifers, and virus-like structures, estimated by the inclusions of apatite grains and by the size of the nuclei, averaged tens of thousands picogram and, consequently, could contain tens of thousands billion pairs of nucleotides. Presumably, the giant genomes of ancient eukaryotes consisted predominantly of non-coding sequences, that served as a reserve that ensures the vital activity of cells when exposed to streams of mutagens from the environment. One of the mutagenic factors could be significant radioactivity, both background and intracellular, caused by high concentrations of radioactive 40K isotope in seawater. The favorable ecological and geochemical environment and the abundance of biophilic elements (especially phosphates) in the waters of the inland basin could play the role of an evolutionary springboard in the history of biosphere evolution.