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On the origin and evolution of life in the Galaxy

Published online by Cambridge University Press:  01 October 2010

Michael McCabe  and
Holly Lucas
Michael McCabe*
Affiliation:
Department of Mathematics, University of Portsmouth, Lion Terrace, Portsmouth, Hants P041 3HF, UK
Holly Lucas
Affiliation:
Department of Mathematics, University of Portsmouth, Lion Terrace, Portsmouth, Hants P041 3HF, UK
*
e-mail: michael.mccabe@port.ac.uk
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Abstract

A simple stochastic model for evolution, based upon the need to pass a sequence of n critical steps is applied to both terrestrial and extraterrestrial origins of life. In the former case, the time at which humans have emerged during the habitable period of Earth suggests a value of n=4. Progressively adding earlier evolutionary transitions gives an optimum fit when n=5, implying either that their initial transitions are not critical or that habitability began around 6 Ga ago. The origin of life on Mars or elsewhere within the Solar System is excluded by the latter case and the simple anthropic argument is that extraterrestrial life is scarce in the Universe because it does not have time to evolve. Alternatively, the timescale can be extended if the migration of basic progenotic material to Earth is possible. If extra transitions are included in the model to allow for Earth migration, then the start of habitability needs to be even earlier than 6 Ga ago. Our present understanding of Galactic habitability and dynamics does not exclude this possibility. We conclude that Galactic punctuated equilibrium, proposed as a way round the anthropic problem, is not the only way of making life more common in the Galaxy.

Keywords

critical evolutionary transitionsEarth migrationevolutionGalactic Habitable ZoneGalaxyhabitabilityorigin of lifestochasticmathematical model
Type
Research Article
Information
International Journal of Astrobiology , Volume 9 , Special Issue 4: Special issue Papers from the Astrobiology Society of Britain Conference 2010 , October 2010 , pp. 217 - 226
Copyright
Copyright © Cambridge University Press 2010

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