The Volyn biota (Ukraine) – indications of 1.5 Gyr old eukaryotes in 3D preservation, a spotlight on the “boring billion”

Abstract

Abstract. The Volyn biota, fossilized organisms with a minimum age of 1.5 Ga, were found in cavities in granitic pegmatites from the Korosten Pluton, NW Ukrainian shield. Fossilization was due to an influx of hydrothermal fluorine-rich waters, which silicified the outermost part of the organisms, thus preserving the 3D morphology. Details of the morphology (investigated by scanning electron microscopy) show that the majority of the specimens are filamentous, of a large variety with diameters ranging from ∼ 10 to ∼ 200 µm, thin filaments with typical branching and thick filaments with ball-shaped outgrowths and dented surface. Filaments can be straight or conical, curvilinear, or strongly curved, up to millimeters in length, some with a central channel. Some filaments show indications of segmentation and are grown as sessile organisms onto substrate; others show both intact ends, indicating a non-sessile, free-living lifestyle. Objects with flaky morphology and agglutinating filaments are interpreted as fossil biofilms. Other objects are hollow and show a large variety of forms; spherical objects are scarce. Infrared spectroscopy indicates the presence of chitosan in one filament type, electron microprobe analysis of nanometer-sized inclusions in filaments identified the presence of Bi(Te,S) minerals, and both observations are compatible with the interpretation as fungi-like organisms. Stable C- and N-isotope data of bulk samples are in the range of −31 ‰ to −47 ‰ δ13C and of +3 ‰ to +10 ‰ δ15N, indicating possible methanogens as part of the subsurface microecosystem. The Volyn biota indicate that at 1.5 Ga complex forms of life existed in the continental deep biosphere, well above the microscopic level, including fungi-like organisms resembling eukaryotes.

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

“…1d-l) were observed, along with indeterminate filaments (Fig. 1m-q) reminiscent of the shapes and diversity depicted by Franz et al (2023) and with similar surface structures, and with one consisting primarily of silica showing an opening at its end (Fig. 1o, p vs fig.…”

“…The authors take this as evidence of a biological origin for the Volyn biota. Chitin is an essential ingredient of the cell walls of fungi, and its presence would support the claim of Franz et al (2023) that morphologies displayed within the Volyn biota can be interpreted as fungal in origin. We note, however, that none of the existing micro-FTIR studies published on fossil fungal remains from a variety of ages and thermal maturities (Fig.…”

“…1). EDX analysis is very similar to the EDAX EDS system used by Franz et al (2023) on selected cross sections (their fig. 10j-l), but it allows elements comprising or attached to the observed objects to be visualised over the entire surface as imaged by SEM (Fig.…”

“…3). Together, these observations raise concern that the material Franz et al (2023) have analysed represents younger fungal contamination. The…”

“…1d-l), we consider the extremely well-preserved specimen illustrated by Franz et al to be a modern trichome. Franz et al (2023) present micro-FTIR spectra intended to allow speculation on the biological affinities of the fossils recovered. Micro-FTIR is a powerful non-destructive technique yielding fundamental information on the molecular structure of organic and inorganic components in a sample by using an infrared source and analysing the absorption spectrum typically in the mid-infrared (approximately 4000 to 400 cm −1 ) region (Chen et al, 2015).…”