Surface and Temporal Biosignatures

Recent discoveries of potentially habitable exoplanets have ignited the prospect of spectroscopic investigations of exoplanet surfaces and atmospheres for signs of life. This chapter provides an overview of potential surface and temporal exoplanet biosignatures, reviewing Earth analogues and proposed applications based on observations and models. The vegetation red-edge (VRE) remains the most well-studied surface biosignature. Extensions of the VRE, spectral "edges" produced in part by photosynthetic or nonphotosynthetic pigments, may likewise present potential evidence of life. Polarization signatures have the capacity to discriminate between biotic and abiotic "edge" features in the face of false positives from band-gap generating material. Temporal biosignatures -- modulations in measurable quantities such as gas abundances (e.g., CO2), surface features, or emission of light (e.g., fluorescence, bioluminescence) that can be directly linked to the actions of a biosphere -- are in general less well studied than surface or gaseous biosignatures. However, remote observations of Earth's biosphere nonetheless provide proofs of concept for these techniques and are reviewed here. Surface and temporal biosignatures provide complementary information to gaseous biosignatures, and while likely more challenging to observe, would contribute information inaccessible from study of the time-averaged atmospheric composition alone.Comment: 26 pages, 9 figures, review to appear in Handbook of Exoplanets. Fixed figure conversion error

Chromite oxidation by manganese oxides in subseafloor basalts and the presence of putative fossilized microorganisms

Chromite is a mineral with low solubility and is thus resistant to dissolution. The exception is when manganese oxides are available, since they are the only known naturally occurring oxidants for chromite. In the presence of Mn(IV) oxides, Cr(III) will oxidise to Cr(VI), which is more soluble than Cr(III), and thus easier to be removed. Here we report of chromite phenocrysts that are replaced by rhodochrosite (Mn(II) carbonate) in subseafloor basalts from the Koko Seamount, Pacific Ocean, that were drilled and collected during the Ocean Drilling Program (ODP) Leg 197. The mineral succession chromite-rhodochrosite-saponite in the phenocrysts is interpreted as the result of chromite oxidation by manganese oxides. Putative fossilized microorganisms are abundant in the rhodochrosite and we suggest that the oxidation of chromite has been mediated by microbial activity. It has previously been shown in soils and in laboratory experiments that chromium oxidation is indirectly mediated by microbial formation of manganese oxides. Here we suggest a similar process in subseafloor basalts

Earth: Atmospheric Evolution of a Habitable Planet

Our present-day atmosphere is often used as an analog for potentially habitable exoplanets, but Earth's atmosphere has changed dramatically throughout its 4.5 billion year history. For example, molecular oxygen is abundant in the atmosphere today but was absent on the early Earth. Meanwhile, the physical and chemical evolution of Earth's atmosphere has also resulted in major swings in surface temperature, at times resulting in extreme glaciation or warm greenhouse climates. Despite this dynamic and occasionally dramatic history, the Earth has been persistently habitable--and, in fact, inhabited--for roughly 4 billion years. Understanding Earth's momentous changes and its enduring habitability is essential as a guide to the diversity of habitable planetary environments that may exist beyond our solar system and for ultimately recognizing spectroscopic fingerprints of life elsewhere in the Universe. Here, we review long-term trends in the composition of Earth's atmosphere as it relates to both planetary habitability and inhabitation. We focus on gases that may serve as habitability markers (CO2, N2) or biosignatures (CH4, O2), especially as related to the redox evolution of the atmosphere and the coupled evolution of Earth's climate system. We emphasize that in the search for Earth-like planets we must be mindful that the example provided by the modern atmosphere merely represents a single snapshot of Earth's long-term evolution. In exploring the many former states of our own planet, we emphasize Earth's atmospheric evolution during the Archean, Proterozoic, and Phanerozoic eons, but we conclude with a brief discussion of potential atmospheric trajectories into the distant future, many millions to billions of years from now. All of these 'Alternative Earth' scenarios provide insight to the potential diversity of Earth-like, habitable, and inhabited worlds.Comment: 34 pages, 4 figures, 4 tables. Review chapter to appear in Handbook of Exoplanet

Luxury without guilt: service innovation in the all-inclusive hotel industry

Services, Hotels, All-inclusive, Non-technological innovation, Business model,

Investigation of Hydrogen Sulfide Exposure and Lung Function, Asthma and Chronic Obstructive Pulmonary Disease in a Geothermal Area of New Zealand

BackgroundResults have been conflicting whether long-term ambient hydrogen sulfide (H2S) affects lung function or is a risk factor for asthma or chronic obstructive pulmonary disease (COPD). Rotorua city, New Zealand, has the world's largest population exposed to ambient H2S-from geothermal sources.ObjectivesWe investigated associations of H2S with lung function, COPD and asthma in this population.Methods1,204 of 1,639 study participants, aged 18-65 years during 2008-2010, provided satisfactory spirometry results. Residences, workplaces and schools over the last 30 years were geocoded. Exposures were estimated from data collected by summer and winter H2S monitoring networks across Rotorua. Four metrics for H2S exposure, representing both current and long-term (last 30 years) exposure, and also time-weighted average and peak exposures, were calculated. Departures from expected values for pre-bronchodilator lung function, calculated from prediction equations, were outcomes for linear regression models using quartiles of the H2S exposure metrics. Separate models examined participants with and without evidence of asthma or COPD, and never- and ever-smokers. Logistic regression was used to investigate associations of COPD (a post-bronchodilator FEV1/FVC ResultsNone of the exposure metrics produced evidence of lung function decrement. The logistic regression analysis showed no evidence that long-term H2S exposure at Rotorua levels was associated with either increased COPD or asthma risk. Some results suggested that recent ambient H2S exposures were beneficially associated with lung function parameters.ConclusionsThe study found no evidence of reductions in lung function, or increased risk of COPD or asthma, from recent or long-term H2S exposure at the relatively high ambient concentrations found in Rotorua. Suggestions of improved lung function associated with recent ambient H2S exposures require confirmation in other studies

Isotopic evidence for biological nitrogen fixation by molybdenum-nitrogenase from 3.2 Gyr

Nitrogen is an essential nutrient for all organisms that must have been available since the origin of life. Abiotic processes including hydrothermal reduction1, photochemical reactions2, or lightning discharge3 could have converted atmospheric N2 into assimilable NH4+, HCN, or NOx species, collectively termed fixed nitrogen. But these sources may have been small on the early Earth, severely limiting the size of the primordial biosphere4. The evolution of the nitrogen-fixing enzyme nitrogenase, which reduces atmospheric N2 to organic NH4+, thus represented a major breakthrough in the radiation of life, but its timing is uncertain5,6. Here we present nitrogen isotope ratios with a mean of 0.0 ± 1.2‰ from marine and fluvial sedimentary rocks of prehnite–pumpellyite to greenschist metamorphic grade between 3.2 and 2.75 billion years ago. These data cannot readily be explained by abiotic processes and therefore suggest biological nitrogen fixation, most probably using molybdenum-based nitrogenase as opposed to other variants that impart significant negative fractionations7. Our data place a minimum age constraint of 3.2 billion years on the origin of biological nitrogen fixation and suggest that molybdenum was bioavailable in the mid-Archaean ocean long before the Great Oxidation Event