Shadow life is a hypothesis proposed by cosmologist Paul Davies, chair of the SETI: Post-Detection Science and Technology Taskgroup of the International Academy of Astronautics. The theory suggests that if life has evolved on Earth more than once, microorganisms may exist on Earth which have no evolutionary connection with any other known form of life. He thinks that if scientists discover an alternate form of microbial life on Earth, the odds are good that life is also common elsewhere in the universe. He suggests that possible indicators could be alternate biochemistries such as right-handed amino acids, or a different genetic code, or even another kind of chemical for its genetic material that are not nucleic acids (DNA nor RNA) chains or biopolymers. The hypothesis speculates that the descendants of any "second genesis" may have survived until today in a shadow biosphere.
- Biological dark matter – An informal term for genetic material or microorganisms that are unclassified or poorly understood
- Hypothetical types of biochemistry
- Shadow biosphere – A hypothetical microbial biosphere of Earth that uses radically different biochemical and molecular processes than currently known life
- The Eerie Silence
- Migneault, Ashley (2009-02-15). "Short Sharp Science: How to hunt for shadow life". Newscientist.com. Retrieved 2010-05-15.
- Morgan, James (2009-02-16). "Alien life 'may exist among us'". BBC News. Retrieved 2015-09-08.
- "Cosmologist Explores Notion Of 'Alien' Life On Earth". Sciencedaily.com. 2009-02-26. Retrieved 2010-05-15.
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