Taphonomic phenomenon of ancient hair from Glacial Beringia: perspectives for palaeoecological reconstructions

An accumulation of mammoth hair, discovered in the Bol'shaya Chukochya River valley (northeast Yakutia, Russia), was found to contain remains of terrestrial and aquatic organisms, including plants, insects, crustaceans, birds and mammals. Radiocarbon dating indicated that this post‐mortem taphocoenosis represented multiple time periods. The mammoth hair was dated to older than 45 ka BP, the plants were dated to 12 750±50 a BP (which corresponds to a shift in the environmental conditions and landscapes during the formation of thermokarst in northeastern Russia) and the bird feathers were dated to 4115±40 a BP. A scenario of the formation of this fossil assemblage is proposed, covering the MIS 3‐1 time range. The hair also yielded various Arctic branchiopod crustaceans, which inhabit shallow temporary water bodies and therefore are important for reconstruction of palaeoenvironments. The cladoceran subgenus Daphnia (Ctenodaphnia), currently absent from the Asian part of Beringia, is reported from this region for the first time. The study demonstrates that the discovered permafrost‐preserved hair is a unique repository of Ice Age organisms.     

Formation of molecules in bright meteors

We calculated equilibrium chemical composition of a mixture of meteoritic vapor and air during fireball events, i.e. during penetration of large meteoroids into terrestrial atmosphere. Different types of fireballs were considered, and calculations were performed for wide ranges of temperatures and pressures. Chemical composition at the quenching point was estimated by comparison of hydrodynamic and chemical reaction time scales. For the typical fireball temperatures of 4000-5000 K, most elements are expected to be in the form of atoms and ions. Notable exceptions are Si and C, which are expected to be mainly in the form of SiO and CO. Other molecules abundant at these temperatures are N₂ and NO. Metal monoxides are most abundant at 2000-2500 K and are formed during the cooling phase. Conditions for formation of other molecules such as , CN, C₂ and OH were also considered. The composition of freshly ablated meteoroid material was studied using the MAGMA code.     

Another Record: Ocean Warming Continues through 2021 despite La Ni?a Conditions

The increased concentration of greenhouse gases in the atmosphere from human activities traps heat within the climate system and increases ocean heat content (O...     

39Ar‐40Ar chronology of the enstatite chondrite parent bodies

Ar‐Ar isochron ages of EL chondrites suggest closure of the K‐Ar system at 4.49 ± 0.01 Ga for EL5 and 6 chondrites, and 4.45 ± 0.01 Ga for EL3 MAC 88136. The high‐temperature release regimes contain a mixture of radiogenic ⁴⁰Ar* and trapped primordial argon (solar or Q‐type) with ⁴⁰Ar/³⁶Ar_TR ~ 0 , which does not affect the ⁴⁰Ar budget. The low‐temperature extractions show evidence of an excess ⁴⁰Ar component. The ⁴⁰Ar/³⁶Ar is 180–270; it is defined by intercept values of isochron regression. Excess ⁴⁰Ar is only detectable in petrologic types >4/5. These lost most of their primordial ³⁶Ar from low‐temperature phases during metamorphism and retrapped excess ⁴⁰Ar. The origin of this excess ⁴⁰Ar component is probably related to metamorphic Ar mobilization, homogenization of primordial and in situ radiogenic Ar, and trapping of Ar by distinct low‐temperature phases. Ar‐Ar ages of EH chondrites are more variable and show clear evidence of a major impact‐induced partial resetting at about 2.2 Ga ago or alternatively, prolonged metamorphic decomposition of major K carrier phases. EH impact melt LAP 02225 displayed the highest Ar‐Ar isochron age of 4.53 ± 0.01 Ga. This age sets a limit of about 25–45 Ma for the age bias between the K‐Ar and U‐Pb decay systems.     

Global coherence of GPS-measured high-frequency surface tremor motions

The traditional approach of GPS investigations is determining trends which are connected with the motion of tectonic plates. At the same time, a global GPS network provides the possibility of investigating statistical properties of high-frequency earth surface tremor in different parts of the world. Based on the results of coherence and correlation analysis of noise components of daily three-component GPS time series, representing measurements of earth surface displacements at 1097 stations, we have found that, during 2010–2011, there was a significant increase in the average level of noise coherence or correlation with dominant periods 7–9 days of surface tremor in nine regions of the earth, and in some of these regions, the average level of coherence or correlation is still high and does not return to the previous level. The increase of the average level of coherence and correlation could be detected on the graphs purely visually, while the middle time point of the time interval in which the ascending occurred is detected more precisely by a formal method based on the use of the Fisher’s ratio.     

The Fe–C–O–H–N system at 6.3–7.8 GPa and 1200–1400 °C: implications for deep carbon and nitrogen cycles

Interactions in a Fe–C–O–H–N system that controls the mobility of siderophile nitrogen and carbon in the Fe⁰-saturated upper mantle are investigated in experiments at 6.3–7.8 GPa and 1200–1400 °C. The results show that the γ-Fe and metal melt phases equilibrated with the fluid in a system unsaturated with carbon and nitrogen are stable at 1300 °C. The interactions of Fe₃C with an N-rich fluid in a graphite-saturated system produce the ε-Fe₃N phase (space group P6₃/mmc or P6₃22) at subsolidus conditions of 1200–1300 °C, while N-rich melts form at 1400 °C. At IW- and MMO-buffered hydrogen fugacity (fH₂), fluids vary from NH₃- to H₂O-rich compositions (NH₃/N₂?>?1 in all cases) with relatively high contents of alkanes. The fluid derived from N-poor samples contains less H₂O and more carbon which mainly reside in oxygenated hydrocarbons, i.e., alcohols and esters at MMO-buffered fH₂ and carboxylic acids at unbuffered fH₂ conditions. In unbuffered conditions, N₂ is the principal nitrogen host (NH₃/N₂?≤?0.1) in the fluid equilibrated with the metal phase. Relatively C- and N-rich fluids in equilibrium with the metal phase (γ-Fe, melt, or Fe₃N) are stable at the upper mantle pressures and temperatures. According to our estimates, the metal/fluid partition coefficient of nitrogen is higher than that of carbon. Thus, nitrogen has a greater affinity for iron than carbon. The general inference is that reduced fluids can successfully transport volatiles from the metal-saturated mantle to metal-free shallow mantle domains. However, nitrogen has a higher affinity for iron and selectively accumulates in the metal phase, while highly mobile carbon resides in the fluid phase. This may be a controlling mechanism of the deep carbon and nitrogen cycles.     

Room semantics inference using random forest and relational graph convolutional networks: A case study of research building

Semantically rich maps are the foundation of indoor location‐based services. Many map providers such as OpenStreetMap and automatic mapping solutions focus on the representation and detection of geometric information (e.g., shape of room) and a few semantics (e.g., stairs and furniture) but neglect room usage. To mitigate the issue, this work proposes a general room tagging method for public buildings, which can benefit both existing map providers and automatic mapping solutions by inferring the missing room usage based on indoor geometric maps. Two kinds of statistical learning‐based room tagging methods are adopted: traditional machine learning (e.g., random forests) and deep learning, specifically relational graph convolutional networks (R‐GCNs), based on the geometric properties (e.g., area), topological relationships (e.g., adjacency and inclusion), and spatial distribution characteristics of rooms. In the machine learning‐based approach, a bidirectional beam search strategy is proposed to deal with the issue that the tag of a room depends on the tag of its neighbors in an undirected room sequence. In the R‐GCN‐based approach, useful properties of neighboring nodes (rooms) in the graph are automatically gathered to classify the nodes. Research buildings are taken as examples to evaluate the proposed approaches based on 130 floor plans with 3,330 rooms by using fivefold cross‐validation. The experiments conducted show that the random forest‐based approach achieves a higher tagging accuracy (0.85) than R‐GCN (0.79).     

L‐chondrite asteroid breakup tied to Ordovician meteorite shower by multiple isochron 40Ar‐39 Ar dating

Abstract— Radiochronometry of L chondritic meteorites yields a rough age estimate for a major collision in the asteroid belt about 500 Myr ago. Fossil meteorites from Sweden indicate a highly increased influx of extraterrestrial matter in the Middle Ordovician ～480 Myr ago. An association with the L‐chondrite parent body event was suggested, but a definite link is precluded by the lack of more precise radiometric ages. Suggested ages range between 450 ± 30 Myr and 520 ± 60 Myr, and can neither convincingly prove a single breakup event, nor constrain the delivery times of meteorites from the asteroid belt to Earth. Here we report the discovery of multiple ⁴⁰Ar‐³⁹Ar isochrons in shocked L chondrites, particularly the regolith breccia Ghubara, that allow the separation of radiogenic argon from multiple excess argon components. This approach, applied to several L chondrites, yields an improved age value that indicates a single asteroid breakup event at 470 ± 6 Myr, fully consistent with a refined age estimate of the Middle Ordovician meteorite shower at 467.3 ± 1.6 Myr (according to A Geologic Time Scale 2004). Our results link these fossil meteorites directly to the L‐chondrite asteroid destruction, rapidly transferred from the asteroid belt. The increased terrestrial meteorite influx most likely involved larger projectiles that contributed to an increase in the terrestrial cratering rate, which implies severe environmental stress.