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Royston, United Kingdom

Bains W.,Massachusetts Institute of Technology | Bains W.,Rufus Scientific Ltd | Seager S.,Massachusetts Institute of Technology | Zsom A.,Massachusetts Institute of Technology

The diversity of extrasolar planets discovered in the last decade shows that we should not be constrained to look for life in environments similar to early or present-day Earth. Super-Earth exoplanets are being discovered with increasing frequency, and some will be able to retain a stable, hydrogen-dominated atmosphere. We explore the possibilities for photosynthesis on a rocky planet with a thin H2-dominated atmosphere. If a rocky, H2-dominated planet harbors life, then that life is likely to convert atmospheric carbon into methane. Outgassing may also build an atmosphere in which methane is the principal carbon species. We describe the possible chemical routes for photosynthesis starting from methane and show that less energy and lower energy photons could drive CH4-based photosynthesis as compared with CO2-based photosynthesis. We find that a by-product biosignature gas is likely to be H2, which is not distinct from the hydrogen already present in the environment. Ammonia is a potential biosignature gas of hydrogenic photosynthesis that is unlikely to be generated abiologically. We suggest that the evolution of methane-based photosynthesis is at least as likely as the evolution of anoxygenic photosynthesis on Earth and may support the evolution of complex life. © 2014 by the authors; licensee MDPI, Basel, Switzerland. Source

Palacios T.,University of Cambridge | Solari C.,University of Cambridge | Bains W.,Rufus Scientific Ltd
Rejuvenation Research

Life expectancy has increased continuously for at least 150 years, due at least in part to improving life conditions for the majority of the population. A substantial part of this historical increase is due to decreases in early life mortality. In this article, we analyze the longevity of four privileged sets of adults who have avoided childhood mortality and lived a life more similar to the modern middle class. Our analysis is focused on writers and musicians from the 17th through the 21st centuries. We show that their average age at death increased only slightly between 1600 and 1900, but in the 20th century increased at around 2 years/decade. We suggest that this confirms that modern life span extension is driven by delay of death in older life rather than avoidance of premature death. We also show that productive life span, as measured by writing and composition outputs, has increased in parallel with overall life span in these groups. Increase in age of death is confirmed in a group of the minor British aristocracy and in members of the US Congress from 1800 to 2010. We conclude that both life span and productive life span are increasing in the 20th and early 21st century, and that the modern prolongation of life is the extension of productive life and is not the addition of years of disabling illness to the end of life. © 2015, Mary Ann Liebert, Inc. Source

Seager S.,Massachusetts Institute of Technology | Schrenk M.,East Carolina University | Bains W.,Massachusetts Institute of Technology | Bains W.,Rufus Scientific Ltd

Microbial life on Earth uses a wide range of chemical and energetic resources from diverse habitats. An outcome of this microbial diversity is an extensive and varied list of metabolic byproducts. We review key points of Earth-based microbial metabolism that are useful to the astrophysical search for biosignature gases on exoplanets, including a list of primary and secondary metabolism gas byproducts. Beyond the canonical, unique-to-life biosignature gases on Earth (O 2, O 3, and N 2O), the list of metabolic byproducts includes gases that might be associated with biosignature gases in appropriate exoplanetary environments. This review aims to serve as a starting point for future astrophysical biosignature gas research. © Copyright 2012, Mary Ann Liebert, Inc. 2012. Source

Seager S.,Massachusetts Institute of Technology | Bains W.,Massachusetts Institute of Technology | Bains W.,Rufus Scientific Ltd | Hu R.,Massachusetts Institute of Technology
Astrophysical Journal

Biosignature gas detection is one of the ultimate future goals for exoplanet atmosphere studies. We have created a framework for linking biosignature gas detectability to biomass estimates, including atmospheric photochemistry and biological thermodynamics. The new framework is intended to liberate predictive atmosphere models from requiring fixed, Earth-like biosignature gas source fluxes. New biosignature gases can be considered with a check that the biomass estimate is physically plausible. We have validated the models on terrestrial production of NO, H2S, CH4, CH 3Cl, and DMS. We have applied the models to propose NH3 as a biosignature gas on a "cold Haber World," a planet with a N 2-H2 atmosphere, and to demonstrate why gases such as CH3Cl must have too large of a biomass to be a plausible biosignature gas on planets with Earth or early-Earth-like atmospheres orbiting a Sun-like star. To construct the biomass models, we developed a functional classification of biosignature gases, and found that gases (such as CH4, H 2S, and N2O) produced from life that extracts energy from chemical potential energy gradients will always have false positives because geochemistry has the same gases to work with as life does, and gases (such as DMS and CH3Cl) produced for secondary metabolic reasons are far less likely to have false positives but because of their highly specialized origin are more likely to be produced in small quantities. The biomass model estimates are valid to one or two orders of magnitude; the goal is an independent approach to testing whether a biosignature gas is plausible rather than a precise quantification of atmospheric biosignature gases and their corresponding biomasses. © 2013. The American Astronomical Society. All rights reserved.. Source

Bains W.,Massachusetts Institute of Technology | Bains W.,Rufus Scientific Ltd | Seager S.,Massachusetts Institute of Technology

Redox chemistry is central to life on Earth. It is well known that life uses redox chemistry to capture energy from environmental chemical energy gradients. Here, we propose that a second use of redox chemistry, related to building biomass from environmental carbon, is equally important to life. We apply a method based on chemical structure to evaluate the redox range of different groups of terrestrial biochemicals, and find that they are consistently of intermediate redox range. We hypothesize the common intermediate range is related to the chemical space required for the selection of a consistent set of metabolites. We apply a computational method to show that the redox range of the chemical space shows the same restricted redox range as the biochemicals that are selected from that space. By contrast, the carbon from which life is composed is available in the environment only as fully oxidized or reduced species. We therefore argue that redox chemistry is essential to life for assembling biochemicals for biomass building. This biomass-building reason for life to require redox chemistry is in addition (and in contrast) to life's use of redox chemistry to capture energy. Life's use of redox chemistry for biomass capture will generate chemical by-products-that is, biosignature gases-that are not in redox equilibrium with life's environment. These potential biosignature gases may differ from energy-capture redox biosignatures. © Mary Ann Liebert, Inc. Source

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