Key traits of living fossil Ginkgo biloba are highly variable but not influenced by climate – Implications for palaeo-pCO2 reconstructions and climate sensitivity

The Ginkgoales, including the ‘living fossil’ Ginkgo biloba, are an important group for stomata-based palaeo-pCO2 reconstructions, with long evolutionary lineages and an extensive, abundant fossil record. The stomatal proxy for palaeo-pCO2 can improve our understanding of the exact relationship between pCO2 and temperatures – Earth's climate sensitivity: a key measure of global warming by pCO2. However, pCO2 records from future climate analogues in the past, such as the mid-Miocene Climatic Optimum, seemingly underestimate pCO2 – climate models cannot simulate the past temperatures with the only moderately elevated pCO2 reconstructed by proxies. Either climate sensitivity must have been elevated, which has implications for future climate forecasts, or proxies underestimate pCO2 due to additional environmental factors. Here we tested whether climate conditions impact stomatal parameters and thus pCO2 reconstruction on a large global database of G. biloba leaves from all continents except Antarctica, spanning 12 climate zones. We reconstructed ambient pCO2 using three stomatal proxy methods (stomatal ratio, transfer functions, Franks gas exchange model) and one stomata-independent isotope-based proxy for comparison (C3 proxy). We found that the stomatal proxy methods reconstructed ambient pCO2 reasonably well and uniformly, but that the C3 proxy underestimated pCO2. All the investigated stomatal parameters displayed an unexpectedly large variability, but no significant relationship with temperature, precipitation, or seasonality. Based on these results, the stomatal proxy is not influenced by climate and specifically does not systematically underestimate pCO2 under high temperatures. Climate sensitivity was likely instead elevated during past global warming episodes, an urgent consideration in climate forecasts for our rapidly warming Earth

The fossil record of igneous rock

A growing awareness of life in deep igneous crust expands our appreciation for life's distribution in the upper geosphere through time and space, and extends the known inhabitable realm of Earth and possibly beyond. For most of life's history, until plants colonized land in the Ordovician, the deep biosphere was the largest reservoir of living biomass. This suggests that deep crustal habitats played an important role in the evolution and development of the biosphere. Paradoxically, the paleo-perspective of deep life has been largely neglected in the exploration of the deep biosphere as well as in paleontology as a whole. Here, we review the collective understanding of the fossil record in igneous crust with the aim to highlight a rising research field with great potential for substantial findings and progress in the near future. We include new results that emphasize the importance of direct or indirect dating of fossils and introduction of new techniques into the field. Currently, an incoherent record of morphological fossils- and chemofossils stretching from present to ~2.4 Ga implies the presence of an abundant and rich, yet largely unexplored, fossil record. Further investigations of deep paleo-environments will most certainly result in substantial insights into the distribution and development of biospheres throughout life's history, the early evolution of prokaryotes and eukaryotes, and Earth's early biogeochemical cycles. We emphasize the fossil record of igneous rock to give it the same status as the fossil record in sedimentary rocks, and to implement fossil investigations as standard procedures in future international drilling campaigns

Metagenomic Analysis from the Interior of a Speleothem in Tjuv-Ante's Cave, Northern Sweden

Speleothems are secondary mineral deposits normally formed by water supersaturated with calcium carbonate percolating into underground caves, and are often associated with low-nutrient and mostly non-phototrophic conditions. Tjuv-Ante’s cave is a shallow-depth cave formed by the action of waves, with granite and dolerite as major components, and opal-A and calcite as part of the speleothems, making it a rare kind of cave. We generated two DNA shotgun sequencing metagenomic datasets from the interior of a speleothem from Tjuv-Ante’s cave representing areas of old and relatively recent speleothem formation. We used these datasets to perform i) an evaluation of the use of these speleothems as past biodiversity archives, ii) functional and taxonomic profiling of the speleothem’s different formation periods, and iii) taxonomic comparison of the metagenomic results to previous microscopic analyses from a nearby speleothem of the same cave. Our analyses confirm the abundance of Actinobacteria and fungi as previously reported by microscopic analyses on this cave, however we also discovered a larger biodiversity. Interestingly, we identified photosynthetic genes, as well as genes related to iron and sulphur metabolism, suggesting the presence of chemoautotrophs. Furthermore, we identified taxa and functions related to biomineralization. However, we could not confidently establish the use of this type of speleothems as biological paleoarchives due to the potential leaching from the outside of the cave and the DNA damage that we propose has been caused by the fungal chemical etching

A historical overview of the Pavilion Lake Research Project-Analog science and exploration in an underwater environment

As humans venture back to the Moon, or onward to near-Earth objects and Mars, it is expected that the rigors of this exploration will far exceed those of Apollo. Terrestrial analogs can play a key role in our preparations for these complex voyages, since in addition to their scientifi c value, analogs afford the exploration community a means to safely prepare and test exploration strategies for future robotic and human planetary missions. Many relevant analog studies exist, and each is focused on a particular aspect of strategic development. Some analog programs such as the Pavilion Lake Research Project (PLRP) present the opportunity to investigate both real scientifi c and real exploration scenarios in tandem. The activities of this research program demand the use of techniques, tools, and strategies for underwater scientifi c exploration, and the challenges associated with the scientifi c exploration of Pavilion Lake are analogous to those human explorers will encounter on other planetary and small solar system bodies. The goal of this paper is to provide a historical synopsis of the PLRP's objectives, milestones, and contributions to both the scientifi c and exploration community. Here, we focus on detailing the development and deployment of an integrated science and exploration program with analog application to our understanding of early Earth systems and the preparation for future human space exploration. Over a decade of exploration and discovery is chronicled herein. © 2011 The Geological Society of America.link_to_subscribed_fulltex