the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 01 Feb 2024
Reply to Comment on Franz et al. (2023): A reinterpretation of the 1.5 billion year old Volyn ‘biota’ of Ukraine, and discussion of the evolution of the eukaryotes, by Head et al. (2023)
Abstract. Head et al. (2023) emphasize the importance of the Volyn biota for the evolution, especially in the so-called ‘boring billion’, in a detailed outline about the biological and geological context. However, they question that the Volyn biota represent Precambrian fossils and instead argue that they are young contaminants of ‘museum dust’. In addition, they postulate that they are of abiotic origin. We present here a detailed discussion of their points of concern based on presented data, including some additional information. Their points of concern were:
- One object, shown by Franz et al. (2023) is similar to a pollen grain, another object is similar to trichomes; we show indications for fossilization and summarize our arguments against ‘museum dust’.
- They question the fossil character of the biota and argue for a biomineralization; we show that the biomineralization in trichomes is distinct from the mineralization of the biota.
- They missed information about the internal structure; we repeat the presented information about the internal structure in more detail, which is also indicative of fossil material and inconsistent with trichomes.
- They argue that we did not compare via infrared spectroscopy the biota with recent fungi; since the biota experienced temperatures near 300 °C, we think that a comparison with thermally degraded chitosan is more appropriate.
- They question the use of strongly negative δ13C as an argument for biotic origin, but we show that in combination with positive δ15N values and the geological situation, a biotic origin is more likely than abiotic synthesis.
In addition, Popov (2023) questioned the age of the Volyn biota, which we postulated as between approximately 1.5 and 1.7 Ga. He argues that the fossils could be Phanerozoic. We will also outline our arguments for the minimum age of 1.5 Ga.
Status: open (extended)
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RC1: 'Comment on egusphere-2024-217', Anonymous Referee #1, 14 Mar 2024
reply
Comment on preprint of Franz et al.: A reinterpretation of the 1.5 billion year old Volyn
2 ‘biota’ of Ukraine, and discussion of the evolution of the eukaryotes, by Head et al. (2023)Franz et al. respond to the comment by Head et.al (2023) on the discussion of the so-called 1.5 billion year old Volny biota, combined with a discussion on the evolution of eukaryotes. Head et al doubt the age of the fossils described and explain them as recent contamination by "museum dust" and some structures are interpreted as non-biological in origin. I already had the original paper by Franz et al 2023 for review and I had considerable problems understanding the preservation of the fossils presented. Some of them seem to have the character of pseudofossils - biomorphs - as described, for example, by Rouillard et al 2018. Head et al. obviously have similar problems and interpret the structures depicted as mentioned above. The arguments presented by Head et al. are largely comprehensible. In the manuscript now presented, Franz et al. attempt to refute the arguments of Head et al.. For me, Franz et al. convincingly describe that the sampling and sample preparation was lege artis. However, dust contamination is often unavoidable. I could imagine that the possible pollen grain (Fig. 6) is such contamination. Franz et al. deny this although the morphological similarity is considerable. The structure in Fig. 2b could also be a dust contamination. In chapter 3 they describe the structure of kerite and explain the presence at the margin in a beryl pseudomorph. They describe that the kerite structure was found in thin sections and is embedded in a C-H containing opal. I am puzzled by the opal, which cannot actually be preserved as such. The organic material has not been analyzed state of the art. It is not clear what the kerite actually is here. They refer here to their work from 2022 where pyrolysis methods were used coupled with a GC, they analyzed mostly aromatic structures and make it difficult to recognize a biological origin. Perhaps Raman spectroscopy would also help to characterize the kerite and also compound-specific d13C analyses. I am not quite sure what they call decayed OM here. In any case, I am convinced that the kerite is pristine and represents a thermally altered OM, but I do not believe that this organic matter is totally of biological origin. I agree with the arguments of Franz et al that the observed "trichomes" do not show biomineralization as Head et al suggest, but show diagenetic-metamorphic mineralization. However, this says nothing about the biogenic character of these structures. Franz et al have measured IR spectra and believe to have analyzed chitosan there - chitosan is formed by deacetylation of chitin. In Franz et al 2023 a FTIR spectrum is shown (Fig.13) in which kerite and chitosan are compared. I think the interpretation is not so convincing, further biogeochemical methods and comparisons would be necessary to confirm the original chitin character. There are also doubts about the age of the kerite, at least the Proterozoic age. Here, too, further dating would be helpful to make the Ar-Ar age measured by Franz et al plausible. Popov 2023 came to an early Paleozoic age. Due to the importance of the age classification of the Volny biota, it seems to me that further analytical action is needed. The origin of the kerite is being discussed and Fischer-Tropsch Type (FTT) processes in the context of serpentinization are, of course, a possibility. However, this requires ultrabasic mineral rocks, which are not to be expected in the immediate vicinity of granite. However, these organic fluids could have migrated, which can also be assumed. However, the very light δ13Corg values of around -50‰ are a problem and indicate an influence of methane metabolism. FTT experiments by McCollum and Seewald 2006 have shown a fractionation step of over 30‰, so that isotopically light Corg values are non-biologically possible. There is also still a need for action here. It cannot be ruled out that the kerite represents a mixed organic matter of FTT products and methane metabolism. There are still many open questions dealing with the so-called Volny biota and the validity as Proterozoic complex fossils is finally not convincing.
Citation: https://doi.org/10.5194/egusphere-2024-217-RC1
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