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Viroids-First—A Model for Life on Earth, Mars and Exoplanets

Institute of Medical Microbiology, University of Zurich, 8006 Zurich, Switzerland
Max Planck Institute for Molecular Genetics, 14195 Berlin, Germany
Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York, NY 10029, USA
Authors to whom correspondence should be addressed.
Geosciences 2019, 9(5), 241;
Received: 13 April 2019 / Revised: 15 May 2019 / Accepted: 22 May 2019 / Published: 25 May 2019
(This article belongs to the Special Issue Planetary Evolution and Search for Life on Habitable Planets)
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The search for extraterrestrial life, recently fueled by the discovery of exoplanets, requires defined biosignatures. Current biomarkers include those of extremophilic organisms, typically archaea. Yet these cellular organisms are highly complex, which makes it unlikely that similar life forms evolved on other planets. Earlier forms of life on Earth may serve as better models for extraterrestrial life. On modern Earth, the simplest and most abundant biological entities are viroids and viruses that exert many properties of life, such as the abilities to replicate and undergo Darwinian evolution. Viroids have virus-like features, and are related to ribozymes, consisting solely of non-coding RNA, and may serve as more universal models for early life than do cellular life forms. Among the various proposed concepts, such as “proteins-first” or “metabolism-first”, we think that “viruses-first” can be specified to “viroids-first” as the most likely scenario for the emergence of life on Earth, and possibly elsewhere. With this article we intend to inspire the integration of virus research and the biosignatures of viroids and viruses into the search for extraterrestrial life. View Full-Text
Keywords: origin of life; ribozyme; RNA world; evolution; Spiegelman‘s Monster; meteorites; endosymbiosis; quasispecies; retroviruses; giant viruses origin of life; ribozyme; RNA world; evolution; Spiegelman‘s Monster; meteorites; endosymbiosis; quasispecies; retroviruses; giant viruses

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Moelling, K.; Broecker, F. Viroids-First—A Model for Life on Earth, Mars and Exoplanets. Geosciences 2019, 9, 241.

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