Recent years have seen rapid developments in the understanding of diagenetic changes to archaeological bones. In particular, the degradation or preservation of proteins and other biomolecules has ...been explored using an increasingly sophisticated battery of analytical techniques. Problems remain, however, in correlating these parameters with physical changes to bone that may be observed microscopically. This is due, in part, to the problems in reproducibly quantifying histological changes to archaeological bone. This paper introduces a novel method for the accurate quantification of these changes employing image analysis of SEM images. Self–consistency of results was tested using measurements of total calcium content at different magnifications. The term ‘bioerosion index’ is suggested for the measured parameter.
An expanded sedimentary section provides an opportunity to elucidate conditions in the nascent Chicxulub crater during the hours to millennia after the Cretaceous‐Paleogene (K‐Pg) boundary impact. ...The sediments were deposited by tsunami followed by seiche waves as energy in the crater declined, culminating in a thin hemipelagic marlstone unit that contains atmospheric fallout. Seiche deposits are predominantly composed of calcite formed by decarbonation of the target limestone during impact followed by carbonation in the water column. Temperatures recorded by clumped isotopes of these carbonates are in excess of 70°C, with heat likely derived from the central impact melt pool. Yet, despite the turbidity and heat, waters within the nascent crater basin soon became a viable habitat for a remarkably diverse cross section of the food chain. The earliest seiche layers deposited with days or weeks of the impact contain earliest Danian nannoplankton and dinocyst survivors. The hemipelagic marlstone representing the subsequent years to a few millennia contains a nearly monogeneric calcareous dinoflagellate resting cyst assemblage suggesting deteriorating environmental conditions, with one interpretation involving low light levels in the impact aftermath. At the same horizon, microbial fossils indicate a thriving bacterial community and unique phosphatic fossils including appendages of pelagic crustaceans, coprolites and bacteria‐tunneled fish bone, suggesting that this rapid recovery of the base of the food chain may have supported the survival of larger, higher trophic‐level organisms. The extraordinarily diverse fossil assemblage indicates that the crater was a unique habitat in the immediate impact aftermath, possibly as a result of heat and nutrients supplied by hydrothermal activity.
Plain Language Summary
The newly formed Chicxulub crater was rapidly filled by seawater then disturbed by tsunami and seiche waves. Sedimentary layers deposited as wave energy declined provide a unique window into the environment of the nascent crater in the months and years to millennia after the impact. Geochemical data show temperatures in hotter regions of the crater in excess of 70°C for the first few years with heat derived from the underlying melt sheet via hydrothermal circulation. Cooler regions of the crater became habitats soon after impact with a suite of fossils indicating diverse life on the seafloor and sea surface, ranging from microbes to marine arthropods, and possibly fish. We suggest that this community was sustained by nutrients and heat from the hydrothermal system. The rapid early recovery in the Chicxulub crater and ocean above demonstrates the resiliency of life under extraordinarily harsh conditions, which has important ramifications for early life on Earth and life on other planets.
Key Points
Sediments derived from decarbonation of the Chicxulub impact target were deposited by tsunami and seiche waves over months to years followed by a layer with atmospheric fallout
Temperatures in the ocean above the hotter regions of the crater were in excess of 70°C, with heat likely derived from the central impact melt pool
Cooler regions within the crater basin became habitats soon after impact with diverse life ranging from microbes to marine arthropods, and possibly fish
Recent years have seen rapid advances in the understanding of diagenetic changes to bone tissues and how these influence the chemistry, microstructure and histological appearance of ancient bone. It ...is now possible to recognise many characteristic features of diagenetically modified bone and this has led to the potential use of these parameters in estimating the potential survival of biogenic signals such as DNA, lipids, proteins and stable isotopes. These characteristic features also hold the potential for preserving a record of different post-mortem environments in individual bones or assemblages of bones from the same site. In sites where the burial conditions have changed over archaeological or geological timescales, histological analyses can shed light on these different burial environments and permit the reconstruction of taphonomic histories of some bones. Examination of polished sections of bone using BSE-SEM has been used to identify characteristic features attributed to aerobic soil bacteria, cyanobacteria, and sulphate reducing bacteria. The approach shows promise for providing supplementary evidence when phasing complex sites, such as graveyards, which developed over several hundred years.
There are several hundred documented finds of “bog bodies” from all over Europe, exhibiting a range of preservation states and spanning nearly all archaeological eras — from Neolithic to Medieval. ...Although these have caught the imagination of both public and academics alike, there is still little consensus on the diagenetic processes that lead to their formation. This work presents early results of an ongoing eight-year project to model some of the processes that lead to the formation of a bog body. The project covers two wetland sites, Rørmyra in Mid-Norway and Lejre in Denmark. Preliminary results show rapid demineralisation of bovine bone and spectacular preservation of pig skin within a raised sphagnum bog in Norway, compared with no detectable demineralisation and poor preservation of skin in a fenland bog in Denmark. Rates of demineralisation at Rørmyra show a linear relationship with time and lead us to predict that a human skeleton may become completely decalcified in approximately 300 years. Electron microscopy of histological sections shows that decalcification proceeds via the natural canalicular network in bone, ultimately leaving a naked collagen matrix that shrinks and cracks on drying.
Human populations have been shaped by catastrophes that may have left long-lasting signatures in their genomes. One notable example is the second plague pandemic that entered Europe in ca. 1,347 CE ...and repeatedly returned for over 300 years, with typical village and town mortality estimated at 10%–40%.1 It is assumed that this high mortality affected the gene pools of these populations. First, local population crashes reduced genetic diversity. Second, a change in frequency is expected for sequence variants that may have affected survival or susceptibility to the etiologic agent (Yersinia pestis).2 Third, mass mortality might alter the local gene pools through its impact on subsequent migration patterns. We explored these factors using the Norwegian city of Trondheim as a model, by sequencing 54 genomes spanning three time periods: (1) prior to the plague striking Trondheim in 1,349 CE, (2) the 17th–19th century, and (3) the present. We find that the pandemic period shaped the gene pool by reducing long distance immigration, in particular from the British Isles, and inducing a bottleneck that reduced genetic diversity. Although we also observe an excess of large FST values at multiple loci in the genome, these are shaped by reference biases introduced by mapping our relatively low genome coverage degraded DNA to the reference genome. This implies that attempts to detect selection using ancient DNA (aDNA) datasets that vary by read length and depth of sequencing coverage may be particularly challenging until methods have been developed to account for the impact of differential reference bias on test statistics.
•The second plague pandemic homogenized ancestry in Trondheim•Gaelic ancestry is sharply reduced in post-pandemic Trondheim•Pervasive reference bias taints frequency differences observed between populations
Gopalakrishnan et al. investigate the genomic signatures of the second plague pandemic on the residents of Trondheim in Norway. They find that the pandemic resulted in a sharp reduction in Gaelic ancestry and also find evidence of differential reference bias among their ancient samples, which reduces the reliability of selection analyses.
PDF
