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Swansong biospheres II: the final signs of life on terrestrial planets near the end of their habitable lifetimes

Published online by Cambridge University Press:  14 January 2014

Jack T. O'Malley-James
School of Physics and Astronomy, University of St. Andrews, North Haugh, St. Andrews, Fife, UK
Charles S. Cockell
UK Centre for Astrobiology, School of Physics and Astronomy, James Clerk Maxwell Building, The King's Buildings, University of Edinburgh, Edinburgh, UK
Jane S. Greaves
School of Physics and Astronomy, University of St. Andrews, North Haugh, St. Andrews, Fife, UK
John A. Raven*
Division of Plant Sciences, University of Dundee at TJHI, The James Hutton Institute, Invergowrie, Dundee, UK


The biosignatures of life on Earth do not remain static, but change considerably over the planet's habitable lifetime. Earth's future biosphere, much like that of the early Earth, will consist of predominantly unicellular microorganisms due to the increased hostility of environmental conditions caused by the Sun as it enters the late stage of its main sequence evolution. Building on previous work, the productivity of the biosphere is evaluated during different stages of biosphere decline between 1 and 2.8 Gyr from present. A simple atmosphere–biosphere interaction model is used to estimate the atmospheric biomarker gas abundances at each stage and to assess the likelihood of remotely detecting the presence of life in low-productivity, microbial biospheres, putting an upper limit on the lifetime of Earth's remotely detectable biosignatures. Other potential biosignatures such as leaf reflectance and cloud cover are discussed.

Research Article
Copyright © Cambridge University Press 2014 

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