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The network of lava tubes is one of the most unexploited natural wonders of the Galapagos Islands. Here, we provide the first morphological, mineralogical, and biogeochemical assessment of speleothems from volcanic caves of the Galapagos to understand their structure, composition, and origin, as well as to identify organic molecules preserved in speleothems. Mineralogical analyses revealed that moonmilk and coralloid speleothems from Bellavista and Royal Palm Caves were composed of calcite, opal-A, and minor amounts of clay minerals. Extracellular polymeric substances, fossilized bacteria, silica microspheres, and cell imprints on siliceous minerals evidenced microbe-mineral interactions and biologically-mediated silica precipitation. Alternating depositional layers between siliceous and carbonate minerals and the detection of biomarkers of surface vegetation and anthropogenic stressors indicated environmental and anthropogenic changes (agriculture, human waste, and cave visits) on these unique underground resources. Stable isotope analysis and Py-GC/MS were key to robustly identify biomarkers, allowing for implementation of future protection policies.

Speleothems represent a valuable archive of paleoclimatic information. In order to identify environmental changes that occurred in the past [1] and to establish protocols for valid models in searching for signs of life in lava tubes, the TUBOLAN and MICROCENO projects study the composition of the organic matter remains preserved in siliceous speleothems in lava tubes from Lanzarote and Selvagens islands, respectively. However, the small size of the samples, their nature, and the challenges of extracting the organic components trapped in them and analyzing with conventional methods, have hindered their use for reconstructing environmental changes [2]. Lanzarote Island offers an extraordinary variety of lava tubes and siliceous speleothems formed through different post-volcanic processes. In addition, Selvagens Islands (Madeira, Portugal) constitute an isolated and undisturbed ecosystem, and consequently, its volcanic caves are a promising model system for investigating pristine biosignatures preserved in siliceous speleothems. Here we show the results of thermal analyses performed on a gypsum core collected in the Inferno Cave (Selvagen Grande Island) and on sediments sampled on the floor of Naturalistas, Las Breñas, and Pescadores caves (Lanzarote). The gypsum core showed the presence of thermostable organic compounds preserved mainly in layers H3-H5 and H7, matching the highest organic carbon contents of the whole profile. The H6 layer shows the presence of organic constituents with contrasting composition. Sediments from Lanzarote lava tubes exhibit a high abundance of organic compounds derived from micro-organisms and the remains of higher plants (leached from the soil above the cave). A complete characterization of the samples, including geochronology, is being performed to relate changes in the speleothems composition to historical episodes of environmental disturbance or/and climatic events. References: [1] Miller, A.Z., De la Rosa, JM, Jimenez-Morillo, NT, Pe

Caves in Selvagen Grande have been reported since more than a century ago, mainly because of their importance in nesting of Cory’s Seawater colonies. Before the Microceno project, only three long caves were known in the island: Furna do Inferno, Furna do Capitão Kidd and Furna do Risco. Considering the volcanic setting of the island with fonolitic and basaltic lava flows, their origin was initially attributed to lava tube genetic processes. The Microceno expedition performed a detailed study of the lithologies and speleogenetic morphologies, documenting additional 10 cavities and discovering also one new important cave, Furna do Sopro du Dragao. The main discovery is that none of these caves are related to volcanic processes. Instead, most of them are formed along sedimentary dikes constituted by bioclastic limestone belonging to Miocenic sedimentary phase intruding the fonolitic basal complex. Internal morphologies indicate that their formation could be related to flank margin speleogenetic processes, due to mixing of seawater with island aquifer along preferential fracture pathways crossing the dikes. To our notice, it is the first case described in the world of a diffuse speleogenesis due to water mixing-corrosion cycles along sedimentary dikes in a predominantly volcanic environment. This has interesting implications for potential karstic processes in volcanic environments on Mars where sedimentary dikes constituted by sulphates have been widely documented by satellite observations and ground rovers.

Together with the Canary and Madeira archipelagos, the Selvagens islands belong to the east North Atlantic volcanic province which insists on the slow moving African plate. They are constituted by two groups of islands and islets pertaining to two central volcanic edifices separated by a NE-SW ridge produced by fissural activity [1]. Thought to be part of the Canary hot spot track, the Selvagens islands are characterized by a very long lived magmatic activity with vigorous stages of volcanism interleaved by long periods of quiescence [2]. In particular, the subaerial part of the NE volcano, corresponding to Selvagem Grande island, records most of the geological evolution of the group which is subdivided into several phases [2]. The shield stage, dated back to the Oligocene (24-26Ma), gave rise to the entire basal complex. It is constituted by phonolites emplaced as lava flows, lava domes, peperites and minor pyroclastic sequence. At 80 m from the sea level a continuous bank of fossiliferous limestones testifies a submarine sedimentation in the early Miocene (13-24 Ma) during a volcanic stasis which was most probably accompanied by an active subsidence proven by numerous sedimentary dykes. A second volcanic pulse is testified by basaltic dykes of the Late Miocene (12-8Ma) crosscutting the calcareous horizon on both islands and often exploiting the sedimentary ones in the Selvagem Grande. In the same island a second magmatic stasis was accompanied by a conglomerates unconformly lying over the previous sequence and was followed by the last volcanic activity at 3.4 Ma which formed the upper volcanic complex characterized by basaltic lavas and breccia erupted from at least three volcanic centers. Caves on Selvagem Grande were developed through the alteration of the peperites of the basal complex and karst action on the sedimentary dykes formed during the early Miocene magmatic stasis. Overall the geological analogies with other planetary contexts, a part for the volcanic

Future human missions to the Moon and Mars will require astronauts to perform science-focused surface exploration in complex geological environments. However, the scientific expertise required for these activities is uncommon in the astronaut corps. PANGAEA (Planetary ANalogue Geological and Astrobiological Exercise for Astronauts) is a field training course designed by the European Space Agency (ESA) that addresses the topics of geological and astrobiological planetary exploration. The course intends to impart the essential basic theoretical and practical knowledge of geology and astrobiology, in order to prepare astronauts for advanced mission specific training. Significant focus is given to skills in areas relevant to future missions, such as scientific decision-making, working with a remotely located science team, and efficient documentation. For this reason, although portions of the course are taught in classrooms, developing independent field skills in analogue geological environments is a key part of the training. Classroom and field lessons are tightly interwoven in the course structure with a time separation often of only hours between being introduced to a concept in the classroom and seeing it in the field. The course forms part of the basic and pre-assignment training for European astronauts and is open to trainees from all other agencies. PANGAEA has been running since 2016, with participants including ESA and NASA astronauts, and Roscosmos cosmonauts, as well as mission designers, operations personnel and engineers. The primary field sites selected for the course are Permo-Triassic sedimentary sequences in the Italian Dolomites, impact lithologies in the Ries Crater, Germany, a comprehensive suite of volcanic deposits in Lanzarote, Spain, and anorthosite outcrops in Lofoten, Norway. Each is used as a base to deliver the main learning sessions, respectively: 1) Earth geology, rock recognition and sedimentology on Earth and Mars, 2) Lunar geology and imp

Volcanic eruptions are geological events spewing large amounts of magma-derived products such as hot lava, volcanic ash, water, and gases. Among the most iconic features of effusive eruptions are lava tubes, which have also been detected on the Moon and Mars. On Earth, these cavities are rapidly colonized by specialized microorganisms, whose growth is fueled by surface-derived organic matter transported via percolation water or by CO2 fixed in situ by chemolithoautotrophic organisms. The likelihood presence of essential life-supporting molecules on Mars, coupled with the interconnection between the origin of life and volcanic eruptions, leads to an intriguing possibility: the existence of specialized chemoautotrophic life within planetary caves. This notion fuels excitement regarding the potential preservation of microbial life within the lava tubes of Mars. Combining microbiological, mineralogical, and organic geochemistry tools, an in-depth characterization of speleothems and associated microbial communities in lava tubes of Lanzarote (Canary Islands, Spain) is provided. The aim is to untangle the underlying factors influencing microbial colonization in Earth’s subsurface in order to gain insight into the possibility of similar subsurface microbial habitats on Mars and to unequivocally identify biosignatures preserved in lava tubes. In this sense, analytical pyrolysis, stable isotope analysis and chemometrics were conducted to characterize the complex organic fraction preserved in speleothems from Lanzarote lava tubes, one of the best terrestrial analogues to Martian volcanology. Our data show that bacterial communities are important contributors to biomarker records in volcanic-hosted speleothems. Within them, the lipid fraction primarily consists of low molecular weight n-alkanes, α-alkenes, and branched-alkenes, providing further evidence that microorganisms serve as the origin of organic matter in these formations. Thus, our research will lay the foundation

Introduction: Secondary minerals identified within lava tubes account for up to 40% of the total number of minerals documented from caves worldwide [1]. Sulfates are by far the most abundant group, but other mineral classes (oxides, hydroxides, etc.) are also present in lava tubes. Key minerals (e.g., gypsum, opal, ice) are used increasingly in answering questions regarding: 1) the source of elemental calcium, sulfur, and oxygen, 2) genetic mechanism including interaction with water of microbial life, and 3) paleoenvironmental information. All these topic could be extremely relevant to planetary cave science [2], and specific cave minerals could be also provide important information on potential biogenetic processes. In this work we present a dataset of secondary minerals from lava tubes belonging to three different volcanic regions of the World.

[Introduction]: Caves are exceptional habitats for highly specialized microorganisms that can interact with minerals, allowing us to better understand the role of microorganisms in biogeochemical cycles and biomineralization processes. These priceless subterranean resources can be found all over the world, but they are one of the least explored habitats on Earth. Yet, lava caves have recently received special attention due to the discovery of numerous volcanic cave entrances on the Moon and Mars [1]. Such subsurface geological settings, characterized by stable physicochemical conditions, may support microbial activity over geological timescales, resulting in the preservation of traces of life in the rock record, recognized as biosignatures. These subterranean environments and the microbial life within thus provide a unique opportunity to study extremely specialized microorganisms, novel metabolic strategies, and interactions with igneous rocks relevant to astrobiology and planetary sciences., [Methods]: The diversity and function of microbial communities dwelling on speleothems from volcanic caves of Selvagens Islands (Madeira, Portugal), La Palma and Lanzarote (Canary Islands, Spain) have been investigated using portable cutting-edge DNAbased analysis, complemented by in-depth metagenomics and field emission scanning electron microscopy (FESEM), to understand which microorganisms grow in these extreme ecosystems, which functional properties they have, and their role in constructive and/or destructive mineral processes. In addition, advanced chromatography, and mass spectrometry techniques, such as GC/MS, PyrolysisGC/Q-TOF and Pyrolysis-compound specific isotope analysis (Py-CSIA) have been employed for an indepth biogeochemical characterization of the siliceous speleothems and for the assessment of biosignatures preserved in the samples, as described in Miller et al. [2,3]., [Results and Discussion]: Bacterial communities showed heterogeneity in composition among lava tubes, with the Actinomycetota, Bacillota and Bacteroidota phyla as the most abundant, exceeding 50% for most of the sampling sites. Using FESEM, we described the morphology of microbial cells and their interactions with the mineral substrate. FESEM images showed abundant actinobacteria-like cells and other morphotypes, resembling those reported by Riquelme et al. [4] in lava tubes from USA, Canada, Portugal and Spain, and in Etna lava tubes [5]. Observations conducted on microbial mat samples from a lava tube in Lanzarote revealed the presence of Ca-rich spheroids closely associated with filamentous cells of Crossiella sp.. The functional profile of microbial communities predicted by PICRUSt showed the presence of urease enzyme, that has been identified as responsible for the microbial precipitation of CaCO3 via urea hydrolysis [6], suggesting that this genus could promote speleothem formation. Similar biogenic-like CaCO3 microspheres were reported in colored microbial mats from Kipuka Kanohina lava cave in Hawaii, USA [4]. The presence of short-chain n-alkanes (C<20) and methylated fatty acids identified in the organic fraction of the siliceous speleothems are recognized as biosignatures of microbial origin (membrane lipids and/or microbial metabolites). High molecular weight lipid compounds (e.g., sterols and long-chain nalkanes) are indicative of vegetation biomarkers derived from lixiviation processes of the soil overlying caves