How cellulose textiles undergo fossilization
Mineralized textile fragment on the surface of a thin copper-based plate from the Nausharo site (Kachi-Bolan region, Balochistan, Pakistan), dated to the first half of the 3rd millennium BCE.
How textiles fossilize in archeological settings remains poorly understood. Cellulose textiles found buried next to metallic objects can undergo a mineralization process that facilitates preservation, but the precise mechanisms are unclear. Corentin Reynaud et al. (pp. 19670–19676) used a combination of analytical techniques to examine the preservation of textiles dating to the 3rd–2nd millennium BCE that were found buried near copper artifacts and sourced from excavations in the Near East and archaeological collections of the Louvre Museum. The techniques included second harmonic generation microscopy, semi-quantitative synchrotron X-ray microtomography, and nanoscale infrared imaging. The analysis uncovered three main stages of preservation through mineralization: water transports soil solutes and antimicrobial cations released by the corrosion of nearby metal to the textile fibers; the fibers absorb the cations and solutes, swell, and form an inorganic crust, resulting in cellulose degradation; and, finally, the fibers undergo silicification, which involves condensation of siliceous compounds. The findings provide insight into the process of mineralization at the nanoscale and how it aids the preservation of textiles that are millennia old. Additionally, the study demonstrates how imaging techniques, including second harmonic generation microscopy, can be used to investigate fossilization of materials, according to the authors. — H.J.
How viruses protect their DNA in extreme environments
Several filamentous viruses that infect hyperthermophilic archaea were isolated from the nearly boiling sulfurous fields of the Campi Flegrei volcano in Pozzuoli, Italy.
Most living organisms use a variety of mechanisms to protect their DNA from degradation, but viruses use only passive means to shield their DNA. To elucidate how viruses might maintain their DNA in extreme environments, Fengbin Wang, Diana Baquero, et al. (pp. 19643–19652) used cryoelectron microscopy to determine the atomic structure of two filamentous viruses—Saccharolobus solfataricus rod-shaped virus 1 and Sulfolobus islandicus filamentous virus—that infect archaeal hosts living in nearly boiling acid springs. The authors found that the capsid proteins in both viruses wrap around the DNA and maintain it in an A-form, which is considered more resistant to degradation than the more common B-form. When the authors compared the structures with those of four other archaeal filamentous viruses, they found structural homology in the capsid proteins—with a relatively conserved fold that wrapped around the A-form DNA—despite having no detectable similarity in sequences, suggesting that all the viruses shared a common ancestry. Similarities between enveloped and nonenveloped archaeal filamentous viruses also suggested that nonenveloped archaeal viruses may have evolved from enveloped viruses by shedding the membrane. The findings shed light on the evolution of viruses. According to the authors, understanding viral structures could aid a variety of biotechnological applications, such as drug delivery and medical imaging. — S.R.
Characterizing snow droughts
Seasonal snowmelt provides freshwater to populations around the world.
Snow is globally important for food, water, and energy security, and snow droughts can have severe social, economic, and environmental consequences. Yet snow droughts remain poorly characterized, with no consistent global framework for monitoring snow droughts. Laurie Huning and Amir AghaKouchak (pp. 19753–19759) developed a standardized approach for assessing deficits in snow water equivalent—the amount of water stored in snow—and characterizing droughts across regions of varying climates and snow regimes around the world. Using this framework, the authors found that in eastern Russia, Europe, and the western United States, snow droughts were longer and more intense during the second half of the period 1980–2018 than during the first half of the same period. The Hindu Kush, Himalayas, extratropical Andes, and Patagonia exhibited the opposite pattern, with shorter and less intense droughts in the latter half of the same period compared with the prior half. The authors note that these changes likely result from a combination of natural and human-induced factors, including Arctic warming, declining sea ice, and shifting of the polar vortex. According to the authors, the framework could be useful for drought monitoring and uncovering physical drivers of snow drought. — B.D.
Rise and fall of Negev viticulture
Wine was an important trade commodity in the Negev desert during the first millennium CE, bringing this peripheral region into an international trade network. Examining the rise and fall of Negev viticulture can offer insight into the development, sustainability, and vulnerability of modern globalized trade networks. Daniel Fuks et al. (pp. 19780–19791) explored three trash mound sites in the Negev, dating to between the 2nd and 8th centuries CE, and used the contents of the mounds as proxies for social and economic conditions. Multiple lines of evidence, including the changing ratio of grape to cereal seeds and of certain types of pottery sherds, charted the rise and fall of viticulture during the Byzantine period. Local viticulture and involvement in Mediterranean trade grew from the 4th to the 6th centuries before peaking and declining in the mid-6th century. The decline was likely attributable to contracting markets, possibly triggered by climate change, plague, or other sociopolitical changes. The authors note that the decline was not a result of the Islamic conquest, which occurred a century later. According to the authors, the economic success of the Byzantine Negev was unsustainable and was an anomaly amid an extended period of seminomadic pastoralism and subsistence farming in the region. — P.G.
Putative early sponge fossil
3D model showing the thicknesses of Namapoikia partitions. This reconstruction was built using serial grinding and neural-network-based image processing.
Skeleton-building animals are crucial to biological and geochemical cycles. Hence, researchers look to the oldest known putative fossilized skeletal animals to determine how and when such an evolutionary development occurred. One genus of such fossils from the Ediacaran period is Namapoikia, hypothesized to be a calcifying sponge. Using serial grinding and neural-network-based image processing, Akshay Mehra et al. (pp. 19760–19766) built and examined 3D reconstructions of two Namapoikia fossils from Namibia. Voids in both samples were large and irregularly distributed, and both partitions and voids varied in thickness between the samples. In contrast, sponges and animals typically build regularly spaced structures. Whereas sponges typically construct canal systems to transport fluid and nutrients throughout the skeleton, no such structures were observed in Namapoikia. Instead, partitions were sheet-like and lacking in chambers. The results suggest that the organism would have resembled meandering and branching ridges emerging from infilling seafloor cement or sediment. This structure is reminiscent of thrombolites and other incrementally growing microbial mats, which, unlike animals, vary in structure and form in response to environmental conditions. According to the authors, the results challenge existing ideas about life before the rise of modern animals. — P.G.
Dietary protein and socioeconomic status
Animal-feeding operations have increased the mass production and availability of animal protein in the United States. To determine whether socioeconomic status (SES) is related to dietary divergence in the United States, James Ehleringer et al. (pp. 20044–20051) collected discarded hair found in trash bins from barbershops and salons across 20 US states and analyzed the carbon and nitrogen isotope ratios in the hair. The authors determined that the collected hair represented samples from 684 individuals. The two primary sources of dietary protein in the samples were identified as animal-derived proteins and plant-derived proteins. Next, the authors correlated the isotope information in the hair samples with US census SES data. Compared with plant-derived proteins, corn-fed animal-derived proteins were more common in the diets of individuals from low SES populations. Animal-derived proteins accounted for 57% of diets on average, and in areas with low SES, they accounted for as much as 75% of diets. The findings suggest that consumption of corn-fed animal proteins is more common among low SES populations than high SES populations, putting low SES populations at a potentially heightened risk of illness, according to the authors. — M.S.