Searching for an alternative form of life on Earth

Research output: Chapter in Book/Report/Conference proceedingConference contribution


Biologists tacitly assume that all life on Earth descended from a common origin. This assumption is based on biochemical similarities and gene sequencing, which enables organisms to be positioned on a common tree of life. However, most terrestrial organisms are microbes, and it is impossible to deduce their biochemical nature from morphology alone. The vast majority of microbes remain unclassified, leaving open the possibility that some of them might be an alternative form of life, arising either from an independent origin, or representing a hitherto overlooked very ancient branch of the known tree. Thus there may exist an extinct, or even extant, shadow biosphere. I discuss various research proposals for locating and identifying "alien" organisms on Earth, both ecologically separate and ecologically integrated.

Original languageEnglish (US)
Title of host publicationInstruments, Methods, and Missions for Astrobiology X
StatePublished - 2007
EventInstruments, Methods, and Missions for Astrobiology X - San Diego, CA, United States
Duration: Aug 28 2007Aug 30 2007

Publication series

NameProceedings of SPIE - The International Society for Optical Engineering
ISSN (Print)0277-786X


OtherInstruments, Methods, and Missions for Astrobiology X
Country/TerritoryUnited States
CitySan Diego, CA


  • Arsenate
  • Biogenesis
  • Impact reseeding
  • Shadow biosphere

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Computer Science Applications
  • Applied Mathematics
  • Electrical and Electronic Engineering


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