In search of future earths: Assessing the possibility of finding earth analogues in the later stages of their habitable lifetimes

© Copyright 2015, Mary Ann Liebert, Inc. Earth will become uninhabitable within 2-3 Gyr as a result of the increasing luminosity of the Sun changing the boundaries of the habitable zone (HZ). Predictions about the future of habitable conditions on Earth include declining species diversity and habitat extent, ocean loss, and changes to geochemical cycles. Testing these predictions is difficult, but the discovery of a planet that is an analogue to future Earth could provide the means to test them. This planet would need to have an Earth-like biosphere history and to be approaching the inner edge of the HZ at present. Here, we assess the possibility of finding such a planet and discuss the benefits of analyzing older Earths. Finding an old-Earth analogue in nearby star systems would be ideal, because this would allow for atmospheric characterization. Hence, as an illustrative example, G stars within 10pc of the Sun are assessed as potential old-Earth-analog hosts. Six of these represent good potential hosts. For each system, a hypothetical Earth analogue is placed at locations within the continuously habitable zone (CHZ) that would allow enough time for Earth-like biosphere development. Surface temperature evolution over the host star's main sequence lifetime (assessed by using a simple climate model) is used to determine whether the planet would be in the right stage of its late-habitable lifetime to exhibit detectable biosignatures. The best candidate, in terms of the chances of planet formation in the CHZ and of biosignature detection, is 61 Virginis. However, planet formation studies suggest that only a small fraction (0.36%) of G stars in the solar neighborhood could host an old-Earth analogue. If the development of Earth-like biospheres is rare, requiring a sequence of low-probability events to occur, biosphere evolution models suggest they are rarer still, with only thousands being present in the Galaxy as a whole

Swansong biospheres: Refuges for life and novel microbial biospheres on terrestrial planets near the end of their habitable lifetimes

The future biosphere on Earth (as with its past) will be made up predominantly of unicellular micro-organisms. Unicellular life was probably present for at least 2.5Â Gyr before multicellular life appeared and will likely be the only form of life capable of surviving on the planet in the far future, when the ageing Sun causes environmental conditions to become more hostile to more complex forms of life. Therefore, it is statistically more likely that habitable Earth-like exoplanets we discover will be at a stage in their habitable lifetime more conducive to supporting unicellular, rather than multicellular life. The end stage of habitability on Earth is the focus of this work. A simple, latitude-based climate model incorporating eccentricity and obliquity variations is used as a guide to the temperature evolution of the Earth over the next 3Â Gyr. This allows inferences to be made about potential refuges for life, particularly in mountains and cold-trap (ice) caves and what forms of life could live in these environments. Results suggest that in high latitude regions, unicellular life could persist for up to 2.8Â Gyr from present. This begins to answer the question of how the habitability of Earth will evolve at local scales alongside the Sun's main sequence evolution and, by extension, how the habitability of Earth-like planets would evolve over time with their own host stars. Copyright © Cambridge University Press 2012

Swansong biospheres: The biosignatures of inhabited earth-like planets nearing the end of their habitable lifetimes

The biosignatures of life on Earth are not fixed, but change with time as environmental conditions change and life living within those environments adapts to the new conditions. A latitude-based climate model, incorporating orbital parameter variations, was used to simulate conditions on the far-future Earth as the Sun enters the late main sequence. Over time, conditions increasingly favour a unicellular microbial biosphere, which can persist for a maximum of 2.8 Gyr from present. The biosignature changes associated with the likely biosphere changes are evaluated using a biosphere-atmosphere gas exchange model and their detectability is discussed. As future Earth-like exoplanet discoveries could be habitable planets nearing the end of their habitable lifetimes, this helps inform the search for the signatures of life beyond Earth Copyright © 2013, International Astronomical Union

From Cytoplasm to Environment: The Inorganic Ingredients for the Origin of Life

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Early in its history, Earth's surface developed from an uninhabitable magma ocean to a place where life could emerge. The first organisms, lacking ion transporters, fixed the composition of their cradle environment in their intracellular fluid. Later, though life adapted and spread, it preserved some qualities of its initial environment within. Modern prokaryotes could thus provide insights into the conditions of early Earth and the requirements for the emergence of life. In this work, we constrain Earth's life-forming environment through detailed analysis of prokaryotic intracellular fluid. Rigorous assessment of the constraints placed on the early Earth environment by intracellular liquid will provide insight into the conditions of abiogenesis, with implications not only for our understanding of early Earth but also the formation of life elsewhere in the Universe.o TEXTO COMPLETO DESTE ARTIGO, ESTARÁ DISPONÍVEL À PARTIR DE AGOSTO DE 2015.133294302Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Universidade de Sao PauloFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

Male-Female Differences in Transitions from First Drug Opportunity to First Use: Searching for Subgroup Variation by Age, Race, Region, and Urban Status

Recent studies in the United States suggest that male-female differences in the prevalence of drug use may result from sex differences in opportunities to use drugs rather than from differences in the likelihood of making a transition into drug use once an opportunity has occurred. That is, men have more opportunities to try drugs, but women appear to be just as likely as men to initiate drug use when given the opportunity to do so. This paper examines whether this general observation holds for subgroups defined by age or birth cohort, race/ethnicity, geographic region, and urban status. We analyzed data from the 1991, 1992, and 1993 National Household Surveys on Drug Abuse. We found general consistency across the subgroups studied. Males were more likely than females to have opportunities to use drugs, but the sexes were equally likely to make a transition into drug use once an opportunity had occurred to try a drug. The implications of this evidence are discussed in relation to the epidemiology and prevention of drug use and with respect to future research on sex and gender differences in drug involvement.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/63334/1/15246090152636550.pd

Identification of 12 new susceptibility loci for different histotypes of epithelial ovarian cancer

To identify common alleles associated with different histotypes of epithelial ovarian cancer (EOC), we pooled data from multiple genome-wide genotyping projects totaling 25,509 EOC cases and 40,941 controls. We identified nine new susceptibility loci for different EOC histotypes: six for serous EOC histotypes (3q28, 4q32.3, 8q21.11, 10q24.33, 18q11.2 and 22q12.1), two for mucinous EOC (3q22.3 and 9q31.1) and one for endometrioid EOC (5q12.3). We then performed meta-analysis on the results for high-grade serous ovarian cancer with the results from analysis of 31,448 BRCA1 and BRCA2 mutation carriers, including 3,887 mutation carriers with EOC. This identified three additional susceptibility loci at 2q13, 8q24.1 and 12q24.31. Integrated analyses of genes and regulatory biofeatures at each locus predicted candidate susceptibility genes, including OBFC1, a new candidate susceptibility gene for low-grade and borderline serous EOC