Ancient Environmental Conditions Research Articles

Contemporary and ancient environmental conditions in the area of the AARI meteorological station Khastyr on Khatanga Bay on Hara-Tumus Peninsular

The aim of the article is to characterize the current and ancient environmental conditions in the area around a new AARI meteorological station, located in the west of the Khara-Tumus Peninsula (73° 49' 39,5'' N 109° 39' 13,5'' E) on the Khatanga Bay of the Laptev Sea. The Khastyr meteorological station was organized in 2016, and for the moment a 6-year (2017–2022) series of hydrometeorological observations has been performed. The average annual temperature at the station is –11.7 °C. The maximum temperature is 31.8 °C, the minimum temperature is –47.3 °C. The annual amount of atmospheric precipitation is 238 mm. The wind blows from west to east or from east to west during most of the year. The maximum wind speed is 28 m/sec, the average wind speed is 5,4 m/sec. The ice cover in the Khatanga Bay disappears in the second part of July and forms again in September-October. The winter lasts here for 9 months of the year.The geological, geomorphological and permafrost structure along the shoreline near the station is investigated.The cliff consists of marine sediments of the Middle and Late Pleistocene. The IR-OSL dating of the sands from the cliff’s basement shows that the sediments are 206 000 year old. The marine sediments, including Karginsky deposits with wood and amber, dated by the radiocarbon method and shown to be 42 000 year old (45 000 calendar year old), are covered by Ice Complex sediments, the mammal bones from which have a radiocarbon age of 32 thousand years (36 thousand calendar years). The saiga (Saiga tatarica) bones found near the Taimyr Peninsula for the first time have a radiocarbon age of 17 thousand 14C years (22 thousand calendar years).Permafrost processes are very active in this area of typical tundra. Therefore, a testing plot for investigating permafrost processes was organized on the territory of the station. Also, this place is very convenient for investigating coastal erosion processes. The Khastyr station can be used as a point for organizing complex studies of the natural environment in a typical tundra on the shore of Khatanga Bay.

Role of Taxa Age and Geologic Range: Survival Analysis of Marine Biota over the Last 538 Million Years

Understanding past extinction processes is an important and current matter, and regression methods in the domain of survival analysis can be applied to fossil data. The chief goal of this study is to relate genus-level lifetimes to ancient environmental conditions (e.g., sea level and surface temperatures or carbon dioxide concentration). The Cox proportional hazards model was used to characterize the extinction risks of marine genera, enabling quantitative and graphical comparisons between selected taxonomic groups over geologic time. The environment was confirmed to be a significant factor, and both age-dependent coefficients and time-dependent covariates were required to accommodate the data. The Cox model analyzed in this study provides new insights into the extinction patterns of marine biota over the past 538.8 million years (Ma). Previous works focusing on specific groups at certain geologic times suggest that the extinction risk is related to taxa age, taxonomic group, and, in some particular cases, geologic time. Here, this idea is confirmed for a larger taxonomic group, during a larger time span (ca. 530 Ma), providing a more complete and complex scenario than previous works. After applying survival analyses, conjoint effects were observed between taxa and their age, their time of existence, and the prevailing environmental conditions found at any particular moment.

Paleosols and ancient societies: from early humans to the industrial revolution

Paleopedology, the study of soils developed on ancient landscapes (Yaalon, 1971), was born in Russia through the efforts of Boris B. Polynov (1927), but considering the previous work done by Vasilli V. Dokuchaev in 1883 (Dokuchaev, 1967) and later with the support of Constantin C. Nikiforoff (1943). The Commission on Paleopedology was established in 1965, in Denver, USA, by Dan Yaalon and Hans van Baren (Retallack, 2013) during the 7th Congress of the International Association for Quaternary Research (INQUA) and later, in 1968, the Commission was affiliated to the International Union of Soil Science (IUSS). After the Denver conference, the Commission published a volume with research papers focused on the recognition and classification of paleosols, methods of dating, and soil stratigraphy (Yaalon, 1971). This volume was the beginning of an extensive series of the Commission publications in different special issues of international and national scientific media. Two of these collections were published in open-access Mexican geological journals: Revista Mexicana de Ciencias Geológicas v. 20 no. 3 (2003) and v. 21 no. 1 (2004), and Boletín de la Sociedad Geológica Mexicana, v. 64 no. 1 and 64 no. 2 (2012). The current issue is a continuation of this series. There are two concepts necessary for understanding paleosols. The first is the use of the uniformitarian principle, which suggests that past geologic processes are similar to those acting today on the Earth’s surface. In other words, the basis of modern soil geography and soil genesis is used as directly analogous to reconstruct ancient environments and landscapes. This approach is more precise when applied to Quaternary paleosols and more limited to pre-Cambrian or Paleozoic paleosols, as the environmental conditions under which they were formed are pretty different from the modern ones (Retallack, 2001). The second concept is “soil memory” (Targulian and Goriachkin, 2004), related to a set of properties that can remember ancient environmental conditions. These properties result from pedogenetic processes and soil-forming factors and are time-resistant to environmental changes remaining stable during extended periods (Targulian and Goriachkin, 2004). In recent years, paleopedology has extended its applications to reconstruct past climates, establish variations in the atmospheric composition, trace the ecosystem evolution, and identify geomorphological changes (e.g., Cerling, 1991; Retallack, 1998, 2009; Goudi, 1990; Klinge et al., 2022). Some efforts have also been made to develop models to quantify pedogenetic trends associated with environmental change (e.g., Yaalon, 1975; Sheldon and Tabor, 2009). An essential application of paleopedology has been devoted to solving archaeological problems, as soils can be considered repositories of human activities: agriculture, forestry, material for construction or ceramic production, dwelling and householding (Holliday, 2009; Costa et al., 2021; Yalçın et al., 2021). The impact of past anthropogenic activities has been recorded in the soil memory through time: since the first hunter and gatherers groups to the industrial societies. However, the relationship between humans and their environment (and vice versa) is complex and demands the application of different methodologies and the study of in-site and off-site approaches (Butzer, 2008), which integrates the information directly recovered in the archaeological excavation and that from the surrounding areas. In this sense, the paleosol-archaeological investigation has a more solid interpretation. In June 2021, the Paleopedology Commission of the IUSS, the Paleopedology Working Group of the INQUA, and the Institute of Geology of the UNAM organized a three-day online meeting with scientific sessions. The meeting topics related to the link between paleosols, the history of human interactions, and the environment. This special issue was launched as a result of this meeting. The articles included here aim to improve our understanding of the materials used for ancient constructions also past human interactions with the environment.

Chemical extraction of iron from carbonate in banded iron formations for isotope analysis

The iron isotope composition of iron-bearing carbonates is commonly used to obtain insights into ancient environmental conditions. However, it is often challenging to target only Fe‑carbonates (e.g. siderite and ankerite) from samples containing a variety of other Fe-bearing minerals, such as observed in Precambrian iron formations. Chemical extraction (i.e. leaching) methods of Fe‑carbonates could be an alternative to in-situ measurements and/or micro-drilling techniques applied to isotopic studies. Yet, only a few studies have looked at the effects of leaching carbonates (e.g. partial and/or total dissolution) on their Fe isotope composition. Here, we tested several leaching protocols, using 5 to 20% acetic acid (HAc) and 0.4 M HCl, on a siderite standard and three natural samples, including an iron formation, Fe-rich and Fe-poor carbonates. We showed that carbonate mineralogy has a strong control on how much of each mineral phase was being dissolved, and that variations in HAc concentration from 5% to 20% are less likely to change how much siderite dissolves (e.g. ∼30% dissolution) under a 12 h period at room temperature. Importantly, the Fe isotope composition of partially dissolved siderite had indistinguishable values within error from the whole-rock composition (i.e. complete dissolution) as shown with HAc and HCl attacks. Carbonates from the three natural samples were almost completely dissolved under the same protocol with 5 to 20% HAc, while 0.4 M HCl attacks dissolved additional mineralogical phases, which might contribute to the Fe leachate. Moreover, the iron isotope composition of carbonate leachates was preserved without generating anomalous results. Hence, weak chemical leaches represent a reliable tool to study Fe isotopic composition of carbonate to understand how the Fe cycle was operating throughout Earth's history.

A preliminary study of early agriculture practices at the Haojiatai site in Luohe city, Henan Province

As the most fundamental economic sector of human societies, farming has played a significant role in interactions between humans and the environment. The study of crop patterns in various regions could not only clarify the economic foundations of early societies, but also greatly improve our understanding of interactions among human beings, the environment, and other creatures. In this regard, this study focuses on early agriculture practices at the Haojiatai site, situated in the cultural and natural transitional region between North and South China. Macro plant remains from this site reveal that foxtail millet was the most important staple crop here during the Longshan and Xinzhai periods (4300-3800 cal. yr BP), along with common millet and a small amount of rice and soybean. This crop pattern is in contrast to the ancient environmental conditions of this region, and cultural factors such as agriculture traditions and food preferences may have been more important in the formation process of this crop pattern.

The <i>Thermosynechococcus</i> Genus: Wide Environmental Distribution, but a Highly Conserved Genomic Core

Cyanobacteria thrive in diverse environments. However, questions remain about possible growth limitations in ancient environmental conditions. As a single genus, the Thermosynechococcus are cosmopolitan and live in chemically diverse habitats. To understand the genetic basis for this, we compared the protein coding component of Thermosynechococcus genomes. Supplementing the known genetic diversity of Thermosynechococcus, we report draft metagenome-assembled genomes of two Thermosynechococcus recovered from ferrous carbonate hot springs in Japan. We find that as a genus, Thermosynechococcus is genomically conserved, having a small pan-genome with few accessory genes per individual strain as well as few genes that are unique to the genus. Furthermore, by comparing orthologous protein groups, including an analysis of genes encoding proteins with an iron related function (uptake, storage or utilization), no clear differences in genetic content, or adaptive mechanisms could be detected between genus members, despite the range of environments they inhabit. Overall, our results highlight a seemingly innate ability for Thermosynechococcus to inhabit diverse habitats without having undergone substantial genomic adaptation to accommodate this. The finding of Thermosynechococcus in both hot and high iron environments without adaptation recognizable from the perspective of the proteome has implications for understanding the basis of thermophily within this clade, and also for understanding the possible genetic basis for high iron tolerance in cyanobacteria on early Earth. The conserved core genome may be indicative of an allopatric lifestyle—or reduced genetic complexity of hot spring habitats relative to other environments.

The global distribution of depositional rivers on early Mars

AbstractSedimentary basins are the archives of ancient environmental conditions on planetary surfaces, and on Mars they may contain the best record of surface water and habitable conditions. While erosional valley networks have been mapped, the global distribution of fluvial sedimentary deposits on Mars has been unknown. Here we generated an eight-trillion-pixel global map of Mars using data from the NASA Context Camera (CTX), aboard the Mars Reconnaissance Orbiter spacecraft, to perform the first systematic global survey of fluvial ridges—exhumed ancient deposits that have the planform shape of river channels or channel belts, but stand in positive relief due to preferential erosion of neighboring terrain. We used large fluvial ridges (>70 m width) as a conservative proxy for the occurrence of depositional rivers or river-influenced depositional areas. Results showed that fluvial ridges are as much as 100 km long, common across the southern highlands, occur primarily in networks within intercrater plains, and are not confined to impact basins. Ridges were dominantly found in Noachian through Late Hesperian units, consistent with cessation of valley network activity, and occurred downstream from valley networks, indicating regional source-to-sink transport systems. These depositional areas mark a globally distributed class of sedimentary deposits that contain a rich archive of Mars history, including fluvial activity on early Mars.

Elemental and Mineral Composition of the Barents Sea Recent and Late Pleistocene−Holocene Sediments: A Correlation with Environmental Conditions

A comprehensive examination of the elemental (including radionuclides and heavy metals), mineral, and grain-size composition of sediments from different areas of the Barents Sea was performed. Sediment cores were sampled in the Central Deep, Cambridge Strait (Franz Josef Land Archipelago), Russkaya Gavan’ Bay (Novaya Zemlya Archipelago), and Bear Island Trough. We aim to evaluate how the modern and more ancient environmental conditions are reflected in the elemental and mineral composition, as well as to test indicative elemental ratios. The applied methods include elemental analysis using gamma-ray spectroscopy, X-ray fluorescence (XRF), Inductively Coupled Plasma-Mass Spectrometry (ICP-MS), and X-Ray Difractometry XRD analysis of minerals. Difference in sedimentation rates, grain-size composition, and sources of material, are reflected in downcore variation of Si/Al, Mn/Fe, P/Al, Ti/K, and quartz-feldspar ratios. At boundary Early Holocene/Late Deglaciation, intensive bottom currents from the West-Southern shelf areas contributed to increase of Si/Al and Zr/Ca ratios. Distinct growth of the Si/Fe ratio within the sediments deposited over Late Pleistocene to Mid Holocene may be caused by increased contents of the coarse sand material, as well as by abundant fluxes of clay-mineral-loaded glacial meltwater during the main deglaciation phase. The Mn/Fe ratio used as redox proxy, displayed peaks at different depths related to oxygen concentration growth in bottom water.

Chlorine Isotope Composition of Apatite from the >3.7 Ga Isua Supracrustal Belt, SW Greenland

The study of the oldest surviving rock suites is crucial for understanding the processes that shaped the early Earth and formed an environment suitable for life. The metasedimentary and metavolcanic rocks of the early Archean Isua supracrustal belt contain abundant apatite, the geochemical signatures of which may help decipher ancient environmental conditions. However, previous research has shown that secondary processes, including amphibolite-facies metamorphism, have reset the original hydrogen isotope composition (δD) of apatite from the Isua belt; therefore, δD values are not indicative of primary conditions in the Archean. Here, we report the first in situ chlorine isotope (δ37Cl) analyses by Secondary Ion Mass Spectrometry (SIMS) from Isua apatite, which we combine with information from transmission electron microscopy, cathodoluminescence imaging, and spectroscopy, documenting the micron-scale internal features of apatite crystals. The determined δ37ClSMOC values (chlorine isotope ratios vs. standard mean ocean chloride) fall within a range from −0.8‰ to 1.6‰, with the most extreme values recorded by two banded iron formation samples. Our results show that δ37Cl values cannot uniquely document primary signatures of apatite crystals, but the results are nonetheless helpful for assessing the extent of secondary overprint.

Testing carbonate-associated sulfate (CAS) extraction methods for sulfur isotope stratigraphy: A case study of a Lower–Middle Ordovician carbonate succession, Shingle Pass, Nevada, USA

Sulfur isotopes measured from sedimentary rocks are used to reconstruct the global sulfur cycle and chemostratigraphic correlation. Relative and absolute changes in the sulfur isotopic composition of the ocean (δ34Sseawater) are essential for estimating changes in redox conditions in ancient environments, particularly for geochemical models that utilize isotope mass balance. Thus, accurate estimates of δ34Sseawater must be measured using a laboratory protocol optimized for the extraction of primary sulfate (preserved as carbonate-associated sulfate; CAS) by removing any contaminant secondary sulfate (e.g., from diagenetic pyrite oxidation).Here we use two CAS-extraction protocols on Lower–Middle Ordovician carbonate rocks to test the degree to which similar absolute values and stratigraphic trends in δ34SCAS are produced by different CAS extraction methods. One method processes carbonate powders once with a single rinse of a 10% NaCl solution to remove sulfate minerals or weakly bonded sulfate ions, followed by a rinse in 5–6% bleach to remove organically bound sulfur before dissolution in hydrochloric acid (HCl). The second method treats carbonate powders with three rinses of NaCl, without a bleach rinse, to more aggressively remove secondary sulfate before dissolution in HCl. Isotopic results show that samples treated in three NaCl rinses produce δ34SCAS values that are on average 7‰ more positive than samples treated with a single NaCl rinse, but a similar stratigraphic trend is preserved in samples processed with either method. We interpret the difference in δ34SCAS between methods to reflect the incomplete removal of secondary sulfate derived from the oxidation of 32S-enriched pyrite when employing only a single NaCl rinse. Surprisingly, rocks with low CAS concentrations (≤10 mg/kg) using both methods show no significant difference in δ34SCAS values, as well as no significant difference in pyrite concentrations and pyrite δ34S (δ34SPY) between methods. Samples with low CAS concentrations are likely altered and secondary sulfate sourced from pyrite oxidation has likely become incorporated into recrystallized carbonate minerals or incorporated into pore-filling calcite cement, all of which is captured as CAS. Results suggest that both CAS-extraction protocols can produce broadly similar δ34SCAS trends, but a single NaCl rinse may not completely remove contaminant sulfate sorbed onto carbonate grains and thus will not yield meaningful data for reconstructing δ34Sseawater. This has clear implications for modeling studies aimed at reconstructing paleo-redox conditions using δ34S data assumed to record global δ34Sseawater trends if these δ34S data are generated using a non-optimized CAS protocol.

Landforms influence the development of ancient agriculture in the Songshan area, central China

The environment exerts a strong influence on the development of ancient agricultural systems, however ancient environmental conditions are often poorly understood in comparison to the development of ancient agricultural systems. In this study, we investigated the temporal patterns of crop distributions from the Neolithic to Bronze Age (9000-2300 yr BP) in the Songshan Mountain area of Henan Province, China in relation to the landforms. Our results show that broomcorn and foxtail were widely distributed across all landforms, regardless of the time period, but more sites are located on hills and mesas and less on the plains. Rice remains dating to the Peiligang period (9000-7000 yr BP) are only found in the plains. While some rice sites are distributed in the hill and mesa areas during the Yangshao period (7000-5000 yr BP), the plains are still the major area where rice sites are found. During the Longshan period (5000-4000 yr BP), soybeans are found at sites located on both mesas and plains. Wheat first appeared during the Erlitou periods (3900-3600 yr BP or 1900–1600 BC) in the region, but the evidence is too limited to determine its landform preference. In the following Shang (3600-3046 yr BP or 1600–1046 BC) and Zhou (3046-2256 yr BP or 1046–256 BC) dynasties, this crop was widely distributed at sites in hills, mesas and plains. Our study reveals that different landforms provide preferred ecological conditions for certain types of agricultural development and played a key role in determining farming styles: dry-farming or rice-farming.

Geomorphic changes along the Yiluo River influenced the emergence of the first urban center at the Erlitou Site, Central Plains of China

Geomorphological research at archaeological sites has shown that ancient environmental conditions have significant implications for understanding changes in archaeological site distribution and layout. The Luoyang Basin in Central China was a center for early urbanism including several large cities in antiquity, but the geomorphic environments that supported these ancient cities have remained uninvestigated. From 2006 to 2011, a field project was conducted in the Luoyang Basin in attempt to understand the relationship between environmental changes and the development of urbanism. Forty-nine profiles were sampled on the alluvial terraces of the Luoyang Basin to examine the geomorphological evolutionary history of the Yi River and Luo River. Our study indicates that the T1 Terrace formed around 7000 cal yr BP and provided a stable landform for Yangshao (7000-5000 yr BP) and Longshan (5000-3900 yr BP) settlements. However, massive floods around 4000-3800 yr BP destroyed some of these late Longshan settlements and caused the Luo River to change its course to southern part of the Luoyang Basin. Those floods significantly altered the landforms and laid a solid foundation for the succeeding development of the urban center at Erlitou.

The paleolimnologist's guide to compound-specific stable isotope analysis – An introduction to principles and applications of CSIA for Quaternary lake sediments

The stable isotope composition of key chemical elements for life on Earth (e.g., carbon, hydrogen, nitrogen, oxygen, sulfur) tracks changes in fluxes and turnover of these elements in the biogeosphere. Over the past 15–20 years, the potential to measure these isotopic compositions for individual, source-specific organic molecules (biomarkers) and to link them to a range of environmental conditions and processes has been unlocked and amplified by increasingly sensitive, affordable and wide-spread analytical technology. Paleoenvironmental research has seen enormous step-changes in our understanding of past ecosystem dynamics. Vital to these paradigm shifts is the need for well-constrained modern and recent analogues. Through increased understanding of these environments and their biological pathways we can successfully unravel past climatic changes and associated ecosystem adaption.With this review, we aim to introduce scientists working in the field of Quaternary paleolimnology to the tools that compound-specific isotope analysis (CSIA) provides for the gain of information on biogeochemical conditions in ancient environments. We provide information on fundamental principles and applications of novel and established CSIA applications based on the carbon, hydrogen, nitrogen, oxygen and sulfur isotopic composition of biomarkers. While biosynthesis, sources and associated isotope fractionation patterns of compounds such as n-alkanes are relatively well-constrained, new applications emerge from the increasing use of functionalized alkyl lipids, steroids, hopanoids, isoprenoids, GDGTs, pigments or cellulose. Biosynthesis and fractionation are not always fully understood. However, although analytical challenges remain, the future potential of deeper insights into ecosystem dynamics from the study of these compounds is also emerging.

DOLOMITE FORMATION BY NANOCRYSTAL AGGREGATION IN THE DOLOMIA PRINCIPALE OF THE BRENTA DOLOMITES (NORTHERN ITALY)

Upper intra- to supratidal laminites in the Norian Dolomia Principale of the Brenta Dolomites (Northern Italy) commonly consist of aphanitic and partially peloidal dolomite previously interpreted as very early diagenetic or penecontemporaneous. Re-examination of a sample prepared by focused ion beam milling through high-resolution transmission electron microscopy (TEM) revealed that dolomicrite crystals may consist of ca. 5-nm-sized nanocrystals characterized by imperfectly aligned orientation. A similar type of dolomite was found in clay-rich Carnian laminites of the Travenanzes Formation (Venetian Alps, Northern Italy) and was interpreted as indication of primary precipitation. The observation of nanocrystals in both the Dolomia Principale and the Travenanzes Formation allows hypothesizing that dolomite mud formed directly from solution via a non-classical pathway involving nucleation and aggregation of nano-particles. Domains of nanocrystalline dolomite in the Dolomia Principale are embedded within, or cemented by, calcian dolomite showing coherent lattice at the micrometre scale and a modulated structure under the TEM. This new finding provides the first evidence that one of the largest dolomite bodies occurring in the geological record, the Dolomia Principale, commenced with deposition of sediment, consisting of dolomite mud formed from solution via non-classical crystallization, and was partially affected by later pervasive diagenetic dolomitization. Based on these new observations we propose that further nano-scale studies are necessary to substantiate the hypothesis that the formation of large dolomite bodies characterized by abundant dolomicrite may have commenced by non-classical nucleation and growth processes. This approach may provide insight on non-actualistic conditions in ancient environments that may have differed, in their boundary conditions, from their modern analogues.

Mineralogical constraints on the thermal history of martian regolith breccia Northwest Africa 8114

Martian meteorite Northwest Africa (NWA) 8114 – a paired stone to NWA 7034 – provides an opportunity to examine the thermal history of a martian regolith and study near-surface processes and ancient environmental conditions near an impact crater on Mars. Our study reports petrographic and alteration textures and focuses on pyroxene and iron oxide grains. Some of the pyroxene clasts show exsolution lamellae, indicating a high temperature magmatic origin and slow cooling. However, transmission electron microscopy reveals that other predominantly pyroxene clasts are porous and have partially re-crystallised to form magnetite and a K-bearing feldspathic glassy material, together with relict pyroxene. This breakdown event was associated with oxidation, with up to 25% Fe3+/ΣFe in the relict pyroxene measured using Fe-K XANES. By comparison with previous studies, this breakdown and oxidation of pyroxene is most likely to be a result of impact shock heating, being held at a temperature above 700 °C for at least 7 days in an oxidising regolith environment.We report an approximate 40Ar-39Ar maximum age of 1.13–1.25 Ga for an individual, separated, augite clast. The disturbed nature of the spectra precludes precise age determination. In section, this clast is porous and contains iron oxide grains. This shows that it has undergone the high temperature partial breakdown seen in other relict pyroxene clasts, and has up to 25% Fe3+/ΣFe. We infer that the age corresponds to the impact shock heating event that led to the high temperature breakdown of many of the pyroxenes, after consolidation of the impact ejecta blanket.High temperatures, above 700 °C, may have been maintained for long enough to remobilise and congruently partially melt some of the alkali feldspar clasts to produce the feldspar veins and aureoles that crosscut, and in some cases surround, the oxidised pyroxene. However, the veins could alternatively be the result of a hydrothermal event in the impact regolith. A simple Fourier cooling model suggests that a regolith of at least five metres depth would be sufficient to maintain temperatures associated with the pyroxene breakdown for over seven days.Low temperature hydrous alteration took place forming goethite, identified via XRD, XANES and FTIR. Comparing with previous studies, the goethite is likely to be terrestrial alteration pseudomorphing martian pyrite.

Resurrecting ancestral genes in bacteria to interpret ancient biosignatures.

Two datasets, the geologic record and the genetic content of extant organisms, provide complementary insights into the history of how key molecular components have shaped or driven global environmental and macroevolutionary trends. Changes in global physico-chemical modes over time are thought to be a consistent feature of this relationship between Earth and life, as life is thought to have been optimizing protein functions for the entirety of its approximately 3.8 billion years of history on the Earth. Organismal survival depends on how well critical genetic and metabolic components can adapt to their environments, reflecting an ability to optimize efficiently to changing conditions. The geologic record provides an array of biologically independent indicators of macroscale atmospheric and oceanic composition, but provides little in the way of the exact behaviour of the molecular components that influenced the compositions of these reservoirs. By reconstructing sequences of proteins that might have been present in ancient organisms, we can downselect to a subset of possible sequences that may have been optimized to these ancient environmental conditions. How can one use modern life to reconstruct ancestral behaviours? Configurations of ancient sequences can be inferred from the diversity of extant sequences, and then resurrected in the laboratory to ascertain their biochemical attributes. One way to augment sequence-based, single-gene methods to obtain a richer and more reliable picture of the deep past, is to resurrect inferred ancestral protein sequences in living organisms, where their phenotypes can be exposed in a complex molecular-systems context, and then to link consequences of those phenotypes to biosignatures that were preserved in the independent historical repository of the geological record. As a first step beyond single-molecule reconstruction to the study of functional molecular systems, we present here the ancestral sequence reconstruction of the beta-carbonic anhydrase protein. We assess how carbonic anhydrase proteins meet our selection criteria for reconstructing ancient biosignatures in the laboratory, which we term palaeophenotype reconstruction.This article is part of the themed issue ‘Reconceptualizing the origins of life’.

Mycology in palaeoecology and forensic science

Palynology (including mycology) is widely used in palaeoecological and bioarchaeological studies. Lake and mire sediments, soils, and the deposits accumulating in archaeological features, invariably contain plant and fungal remains, particularly pollen and spores. These serve as proxy indicators of ancient environmental conditions and events. Forensic palynology has been successfully employed in criminal investigations for more than two decades. In recent years, it has included fungal palynomorphs in profiling samples from crime scenes, and from exhibits obtained from suspects and victims. This contribution outlines the main features of palynology, and gives examples of case studies where fungal spores, pollen, and plant spores, have enhanced the interpretation of ancient landscapes and land-use, and provided pivotal intelligence, and probative evidence, in criminal investigations.

Paleoenvironmental proxies in echinoid spines (Eucidaris galapagensis, Döderlein 1887) along a natural water temperature gradient

The use of paleoenvironmental proxies such as oxygen isotopes in echinoderm skeletons has been a matter of controversial debate. Many previous studies showed a variety of environmental as well as biological processes causing deviations from equilibrium incorporation of geochemical proxies during the formation of echinoderm skeletons. However, given the global distribution of echinoids, their fast spine growth and their occurrence throughout the entire Phanerozoic, species-specific calibrations of geochemical proxies in echinoid spines can disclose a valuable bio-archive for reconstructing ancient environmental conditions throughout Earth's history if samples are adequately preserved in the sedimentary record.Here we present data on oxygen isotopes (δ18O), carbon isotopes (δ13C), and Mg/Ca ratios measured in Eucidaris galapagensis (Döderlein, 1887) spines, which were sampled along the natural water temperature gradient of the Galápagos archipelago. We found a negative correlation of δ18OCalcite with ambient water temperature following the equation 1000ln(α)=23.03(103T−1[K])−47.90. We also found δ13CCalcite be positively correlated with water temperature following the equation δ13CCalcite(VPDB)=−47.585+(0.164∗T[K]. Mg/Ca ratios also showed a significant correlation with water temperature, however, with a low correlation coefficient. The large scatter of δ18OCalcite values within the upwelling region indicates higher growth rates during seasons of colder water temperatures. Considering this and the observed steeper slope in the temperature-δ18OCalcite relationship, our data suggest that the common assumption of respiration affecting oxygen isotope fractionation does not apply for the tropical species E. galapagensis. Overall, our data show that E. galapagensis spines represent valuable paleoenvironmental archives which might have the potential to provide sub-annually resolved water temperature records if spine architecture and growth pattern are well constrained.

δ18O and δ13C Variability In Brachiopods From Modern Shelf Sediments and Its Utility For Understanding Complex Oceanography, Southern Australian Shelf

Abstract The δ18O and δ13C values of brachiopod shell calcite are commonly used as proxies for ancient environmental marine conditions and secular changes in ancient ocean chemistry. The variability of δ18O and δ13C across modern shelf settings is, however, not well documented. This study presents δ18O and δ13C data from 407 Holocene (< 5000 yr BP) and living brachiopods collected from 220 sites across ∼ 3000 km along Australia’s southern shelf, the largest cool-water carbonate shelf in the modern world. Significant isotopic variability is present in separate specimens, at individual sites, and across the entire region. Individual specimens analyzed at multiple shell positions have an isotopic range of values up to 1.3‰ and 1.9‰ for δ18O and δ13C respectively. Multiple brachiopods at a single site have values that vary as much as 2.1‰ for δ18O and 1.8‰ for δ13C. Regional variability ranges on the order of 3.6‰ and 3.4‰, for δ18O and δ13C respectively. The distribution of intrasite variability can be divided into areas of high and low variability. Areas characterized by low variability occur in zones of relatively consistent shelf water conditions. High-variability zones usually correspond to areas of seasonal upwelling onto the shelf, and this aspect is interpreted to be the main cause of isotopic variability. Upwelling waters are cold, leading to higher δ18O values, and are commonly rich in respired dissolved inorganic carbon (DIC) and nutrients, promoting active phytoplankton growth and leading to variable δ13C values. The extensive spatial coverage across this vast latitude-parallel region provides a valuable baseline illustrating the isotopic range that could occur in a single layer in the rock record. Furthermore, changes in isotopic signatures measured across stratigraphy might not necessarily reflect secular changes in ocean chemistry but, instead, could be recording local changes in shelf circulation and upwelling intensity.

Modern Black Sea oceanography applied to the end-Permian extinction event

The modern Black Sea has a mixed upper layer in the top 150–200 m of the water column, below which the water is anoxic, separated from the mixed layer by a redox boundary. There is limited vertical movement of water. Pyrite framboids form in the water column of the anoxic zone, then have been traditionally interpreted to sink immediately and accumulate in the sediments of the Black Sea. Thus the occurrence of framboids in sediments in the rock record is widely interpreted to indicate poorly oxygenated to anoxic conditions in ancient environments. However, in the Permian–Triassic boundary (PTB) microbialites of South China, which formed in shallow marine conditions in contact with the atmosphere, the published occurrence of framboids is inconsistent with abundant gastropod and ostracod shells in the microbialite. Furthermore, in the modern Black Sea, (a) framboids may be suspended, attached to organic matter in the water column, thus not settle to the sea floor immediately after formation; and (b) the redox zone is an unstable complex area subject to rapid vertical water movement including occasional upwelling. The model presented here supposes that upwelling through the redox zone can lead to upward transport of suspended pyrite framboids into the mixed layer. Advective circulation could then draw suspended framboids onto the shelf to be deposited in oxygenated sediments. In the Permian–Triassic transition, if framboids were up-welled from below the redox boundary and mixed with oxygenated waters, sediment deposited in these conditions could provide a mixed signal for potentially misleading interpretations of low oxygen conditions. However, stratigraphic sampling resolution of post-extinction microbialites is currently insufficient to demonstrate possible separation of framboid-bearing layers from those where framboids are absent.Profound differences between microbialite constructors and sequences between the western and eastern Tethys demonstrate barriers to migration of microbial organisms. However, framboid occurrences in both areas indicate upwelling and emphasize vertical movement of water from the lower to upper ocean, yet the mixed layer advective motion may not have been as effective as in modern oceans. In the modern Black Sea, such advection is highly effective in water mixing, and provides an interesting contrast with the PTB times.