Jennifer M. K. O'KEefe

Ultramafic minerals from the Goat Hill serpentine barrens, Chester County, Pennsylvania, were examined using scanning electron and transmission electron microscopy in conjunction with energy dispersive spectroscopy, selected area electron diffraction, and electron energy loss spectroscopy. Magnesium-rich lizardite and clinochlore, antigorite, chrysotile, gahnite, Fe- and Fe-Cr spinels, and vernadite were the primary minerals with amorphous phases interspersed with the minerals. The Mn-oxide vernadite had a mixed Mn⁴⁺/Mn³⁺ oxidation state, with Mn⁴⁺ > Mn³⁺ and Ni > Fe.

End of 21st‐century hydroclimate projections suggest an expansion of subtropical dry zones, with Mediterranean and Sahel regions becoming much drier. However, paleobotanical assemblage evidence from the middle Miocene (17‐12 Ma), suggests both regions were instead humid environments. Here we show that by modifying regional sea surface temperatures (SST) in an Earth System Model (CESM1.2) simulation of the middle Miocene, the increased ocean evaporation and integrated water vapor flux overrides any drying effects associated with warming‐induced land‐surface evaporation driven by atmospheric CO₂ concentrations. These modifications markedly reduce the bias in the model‐data comparison for this period. A vegetation model (BIOME4) forced with simulated climatologies predicts both regions were dominated by mixed forest, which is largely consistent with the paleobotanical record. This study unveils the potential for wetter subtropical Mediterranean climates associated with warming, presenting an alternative scenario from future drying projections with localized SST warming governing regional climate change.

Franz et al. (2023) report a diverse and three-dimensionally preserved suite of mid-Proterozoic microfossils from miarolitic cavities within the granitic Volyn pegmatite field, a major granitic plutonic complex in NW Ukraine. The biota is dated at between ∼ 1.76 and ∼ 1.5 Ga and includes fungus-like objects. This biota is reported as evidence of organisms living within the continental lithosphere, illuminating part of a ∼ 1.8–0.8-billion-year interval of the Proterozoic Eon characterised by relatively low climatic variability and slow biological evolution. We show that at least some of this putative diversity represents modern contamination including plant hairs, a distinctive pollen grain assignable to the extant conifer genus Pinus, and likely later fungal growth. Comparable diversity is shown to exist in modern museum dust, presented as an example of potential airborne contamination and calling into question whether any part of the Volyn “biota” is biological in origin. We emphasise the need for scrupulous care in collecting, analysing, and identifying Precambrian microfossils.

Franz et. al. (Biogeosciences 20, 1901–1924, 2023) report a diverse and three-dimensionally preserved suite of mid-Proterozoic microfossils from miarolotic cavities within the granitic Volyn pegmatite field, a major granitic plutonic complex in NW Ukraine. The biota is dated at between ~1.76 Ga and ~1.5 Ga and includes fungus-like objects. This biota is reported as evidence of organisms living within the continental lithosphere, illuminating part of a ~1.8–0.8 billion year interval of the Proterozoic Eon characterised by relatively low climatic variability and slow biological evolution. We show that at least some of this putative diversity represents modern contamination including plant hairs, a distinctive pollen grain assignable to the extant conifer genus Pinus, and likely later fungal growth. Comparable diversity is shown to exist in modern museum dust, this calling into question whether any part of the Volyn ‘biota’ is biological in origin while emphasising the need for scrupulous care in collecting, analysing, and identifying Precambrian microfossils.

Franz et. al. (Biogeosciences 20, 1901–1924, 2023) report a diverse and three-dimensionally preserved suite of mid-Proterozoic microfossils from miarolotic cavities within the granitic Volyn pegmatite field, a major granitic plutonic complex in NW Ukraine. The biota is dated at between ~1.76 Ga and ~1.5 Ga and includes fungus-like objects. This biota is reported as evidence of organisms living within the continental lithosphere, illuminating part of a ~1.8–0.8 billion year interval of the Proterozoic Eon characterised by relatively low climatic variability and slow biological evolution. We show that at least some of this putative diversity represents modern contamination including plant hairs, a distinctive pollen grain assignable to the extant conifer genus Pinus, and likely later fungal growth. Comparable diversity is shown to exist in modern museum dust, this calling into question whether any part of the Volyn ‘biota’ is biological in origin while emphasising the need for scrupulous care in collecting, analysing, and identifying Precambrian microfossils.

Franz et. al. (Biogeosciences 20, 1901–1924, 2023) report a diverse and three-dimensionally preserved suite of mid-Proterozoic microfossils from miarolotic cavities within the granitic Volyn pegmatite field, a major granitic plutonic complex in NW Ukraine. The biota is dated at between ~1.76 Ga and ~1.5 Ga and includes fungus-like objects. This biota is reported as evidence of organisms living within the continental lithosphere, illuminating part of a ~1.8–0.8 billion year interval of the Proterozoic Eon characterised by relatively low climatic variability and slow biological evolution. We show that at least some of this putative diversity represents modern contamination including plant hairs, a distinctive pollen grain assignable to the extant conifer genus Pinus, and likely later fungal growth. Comparable diversity is shown to exist in modern museum dust, this calling into question whether any part of the Volyn ‘biota’ is biological in origin while emphasising the need for scrupulous care in collecting, analysing, and identifying Precambrian microfossils.

Franz et. al. (Biogeosciences 20, 1901–1924, 2023) report a diverse and three-dimensionally preserved suite of mid-Proterozoic microfossils from miarolotic cavities within the granitic Volyn pegmatite field, a major granitic plutonic complex in NW Ukraine. The biota is dated at between ~1.76 Ga and ~1.5 Ga and includes fungus-like objects. This biota is reported as evidence of organisms living within the continental lithosphere, illuminating part of a ~1.8–0.8 billion year interval of the Proterozoic Eon characterised by relatively low climatic variability and slow biological evolution. We show that at least some of this putative diversity represents modern contamination including plant hairs, a distinctive pollen grain assignable to the extant conifer genus Pinus, and likely later fungal growth. Comparable diversity is shown to exist in modern museum dust, this calling into question whether any part of the Volyn ‘biota’ is biological in origin while emphasising the need for scrupulous care in collecting, analysing, and identifying Precambrian microfossils.