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.

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 similar to 10 to similar to 200 mu m, 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 parts per thousand to -47 parts per thousand delta C-13 and of +3 parts per thousand to +10 parts per thousand delta N-15, 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.

Green beryl and the yellow beryl variety heliodor are well known from the Volyn pegmatite field in Ukraine, and this study presents details of their morphological characteristics. Visible etch pits are characteristic of beryl from this locality. In addition, they may contain an organic matter called kerite. Formation of the etch pits is associated with a fluorine-rich, late-stage fluid phase. Etch pits on the pinacoidal face have a hexagonal outline and a pointed bottom (originating at linear defects) transitioning to etch pits with very steep walls, and they occur in three different orders of magnitude: <= 500 mu m, <= 50 mu m, and 1-3 mu m. On the first-order prismatic faces, etch pits with a flat bottom (originating from point defects) or pointed bottom are square to rectangular, the latter oriented parallel or perpendicular to the beryl's c-axis. Flat bottom etch pits are more abundant than pointed bottom and also occur in three different orders of magnitude. In addition, small etch pits with a canoe shape and porosity on the nanometer scale were observed. Scanning electron microscopy of these etch pits was used to distinguish uncut stones from other pegmatitic beryls, but these phenomena are also visible with an optical microscope or even with a loupe.

The Volyn biota, fossilized organisms with a minimum age of 1.5 Ga, were found in cavities in 21 granitic pegmatites from the Korosten pluton, NW Ukrainian shield. Fossilization was due to 22 influx of hydrothermal fluorine-rich waters, which silicified the outermost part of the 23 organisms, thus preserving the 3D morphology. Details of the morphology (investigated by 24 scanning electron microscopy) show that the majority of the specimens is filamentous, of a 25 large variety with diameters ranging from ~10 µ m to ~200 µ m, thin filaments with typical 26 branching, thick filaments with ball-shaped outgrowths and dented surface. Filaments can be 27 straight or conical, curvilinear or strongly curved, up to mm in length, some with a central 28 channel. Some filaments show indications for segmentation, are grown as sessile organisms onto substrate; others both intact ends, indicating growth in soft medium or floating in water. Objects flaky morphology and agglutinating filaments are interpreted as fossil biofilms. Other objects are hollow and show a large variety of forms; spherical objects are 32 scarce. Infrared spectroscopy indicates the presence of chitosan in one filament, electron microprobe analysis of nm-sized inclusions in filaments identified the presence of Bi(Te,S) minerals, and both observations are compatible with the interpretation of filaments as fungi- 35 like organisms. Stable C- and N-isotope data of bulk samples are in the range of -31 to -47 ‰ 36 d 13 C/ 12 C, and of +3 to +10 ‰ d 15 N/ 14 N, indicating possible methanogenic bacteria as part of 37 the subsurface micro-ecosystem. The Volyn biota show that at 1.5 Ga fungi-like organisms 38 lived in the continental deep biosphere, where complex forms of life existed, well above the 39 microscopic level. 40

We report on Precambrian microfossils from igneous rocks of the Volyn pegmatite district, associated with the Paleoproterozoic Korosten pluton, northwestern Ukraine. The fossils were recovered from meter-sized miarolitic cavities and show a well-preserved 3D morphology, mostly filamentous but with a large variety of types and also in irregular, flaky shapes reminiscent of former biofilms, as well as rare spherical objects. Based on literature data, pyrolysis experiments, and reflected light microscopy results, the organic matter (OM) is characterized as (oxy-)kerite. Further investigations with microscopic techniques, including scanning and transmission electron microscopy, and electron microprobe analysis show that fossilization likely occurred during a hydrothermal, post-pegmatitic event by silicification dominantly in the outermost 1–2 µm of the microfossils. The hydrothermal fluid, derived from the pegmatitic environment, was enriched in SiF4, Al, Ca, Na, K, Cl, and S. The OM shows O enrichment in which N and S content is low, indicating simultaneous N and S loss during anaerobic oxidation. Mineralization with Al silicates starts at the rim of the microfossils, continuing in its outer parts into identifiable encrustations and intergrowths of clay minerals, feldspar, Ca sulfate, Ca phosphate, Fe sulfide, and fluorite. Breccias, formed during collapse of some the miarolitic cavities, contain decaying OM, which released high concentrations of dissolved NH4+, responsible for the late-stage formation of tobelite-rich muscovite and buddingtonite. The age of the fossils can be restricted to the time between the pegmatite formation, at ∼1.760 Ga, and the breccia formation at ∼1.49 Ga. As the geological environment for the growth of the microorganisms and fossilization, we assume a geyser system in which the essential biological components C, N, S, and P for growth of the organisms in the miarolitic cavities were derived from microorganisms at the surface. Fossilization was induced by magmatic SiF4-rich fluids. The Volyn occurrence is a distinct and uncommon example of Precambrian fossils, and the results underline the importance of cavities in granitic rocks as a possible habitat for microorganisms preserved in the deep biosphere.

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 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 is filamentous, of a large variety with diameters ranging from ~10 µm to ~200 µm, thin filaments with typical branching, thick filaments with ball-shaped outgrowths and dented surface. Filaments can be straight or conical, curvilinear or strongly curved, up to mm in length, some with a central channel. Some filaments show indications for segmentation, are grown as sessile organisms onto substrate; others show both intact ends, indicating growth in soft medium or floating in water. 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, electron microprobe analysis of nm-sized inclusions in filaments identified the presence of Bi(Te,S) minerals, and both observations are compatible with the interpretation of filaments as fungi-like organisms. Stable C- and N-isotope data of bulk samples are in the range of -31 to -47 ‰ δ13C/12C, and of +3 to +10 ‰ δ15N/14N, indicating possible methanogenic bacteria as part of the subsurface micro-ecosystem. The Volyn biota show that at 1.5 Ga fungi-like organisms lived in the continental deep biosphere, where complex forms of life existed, well above the microscopic level.