Abstract
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.
Highlights
The search for extraterrestrial life, recently fueled by the discovery of exoplanets, requires defined biosignatures
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
There are viruses of plants and fungi including Turnip Yellow Mosaic Virus, Brome Mosaic Virus or Narnaviruses that contain a transfer RNAs (tRNAs)-like structure linked to an amino acid such as valine, histidine, or tyrosine
Summary
Exoplanets orbit around central stars distinct from our Sun. The number of detected exoplanets is increasing rapidly; 3800 have been discovered by 2018, 2300 of them by the Kepler telescope that recently stopped transmitting signals. There are an estimated 1010 exoplanets in our galaxy, and 1025 in the entire Universe [2] This enormous number makes it likely that some form of life exists somewhere else. Robots may collect samples on planets within our galaxy, perform experiments and transmit data. Sequencing instruments such as Oxford Nanopore may be used to detect and sequence nucleic acids. Earth ~4.5 Bya. The elements that originate from star dust, and are initial building blocks for life on. It was initially closer to Earth and drifts away by 3.8 cm per year It is at a distance of 384,000 km (238606 miles), close enough for manned missions. Oxygen may be an indicator of life on other planets [11]
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