Life Warning: You are not logged in. Your IP address will be publicly visible if you make any edits. If you log in or create an account, your edits will be attributed to your username, along with other benefits.Anti-spam check. Do not fill this in! === Challenge === The definition of life has long been a challenge for scientists and philosophers.<ref name="Definitions 2009">{{cite journal |title=Why Is the Definition of Life So Elusive? Epistemological Considerations |journal=Astrobiology |date=May 2009 |last=Tsokolov |first=Serhiy A. |volume=9 |issue=4 |doi=10.1089/ast.2007.0201 |bibcode=2009AsBio...9..401T |pages=401β412 |pmid=19519215}}</ref><ref name=Emmeche1997>{{cite web |first1=Claus |last1=Emmeche |year=1997 |title=Defining Life, Explaining Emergence |publisher=Niels Bohr Institute |url=http://www.nbi.dk/~emmeche/cePubl/97e.defLife.v3f.html |access-date=25 May 2012 |url-status=dead |archive-url=https://web.archive.org/web/20120314095044/http://www.nbi.dk/~emmeche/cePubl/97e.defLife.v3f.html |archive-date=14 March 2012 }}</ref><ref name=McKay>{{Cite journal |title=What Is Lifeβand How Do We Search for It in Other Worlds? |journal=PLOS Biology |date=14 September 2004 |first=Chris P. |last=McKay |pmid=15367939 |volume=2 |issue=9 |pmc=516796 |page=302 |doi=10.1371/journal.pbio.0020302 |doi-access=free }}</ref> This is partially because life is a process, not a substance.<ref name="DefinitionMotivation">{{Cite journal |last=Mautner |first=Michael N. |title=Directed panspermia. 3. Strategies and motivation for seeding star-forming clouds |journal=Journal of the British Interplanetary Society |year=1997 |volume=50 |pages=93β102 |url=http://www.astro-ecology.com/PDFDirectedPanspermia3JBIS1997Paper.pdf |bibcode=1997JBIS...50...93M |url-status=live |archive-url=https://web.archive.org/web/20121102064738/http://www.astro-ecology.com/PDFDirectedPanspermia3JBIS1997Paper.pdf |archive-date=2 November 2012 }}</ref><ref name="SeedingBook">{{Cite book |last=Mautner |first=Michael N. |title=Seeding the Universe with Life: Securing Our Cosmological Future |date=2000 |isbn=978-0-476-00330-9 |url=http://www.astro-ecology.com/PDFSeedingtheUniverse2005Book.pdf |url-status=live |archive-url=https://web.archive.org/web/20121102064713/http://www.astro-ecology.com/PDFSeedingtheUniverse2005Book.pdf |archive-date=2 November 2012 }}</ref><ref>{{cite journal |title=What is life? It's a Tricky, Often Confusing Question |journal=Astrobiology Magazine |date=18 September 2014 |last=McKay |first=Chris}}</ref> This is complicated by a lack of knowledge of the characteristics of living entities, if any, that may have developed outside Earth.<ref>{{Cite journal |last1=Nealson |first1=K.H. |last2=Conrad |first2=P.G. |title=Life: past, present and future |journal=[[Philosophical Transactions of the Royal Society of London B]] |volume=354 |issue=1392 |pages=1923β1939 |date=December 1999 |pmid=10670014 |pmc=1692713 |doi=10.1098/rstb.1999.0532 |url=https://royalsociety.org/journals/|archive-date=3 January 2016 |archive-url=https://wayback.archive-it.org/all/20160103000925/https://royalsociety.org/journals/ |url-status=live }}</ref><ref name="Bioethics">{{Cite journal |last=Mautner |first=Michael N. |title=Life-centered ethics, and the human future in space |journal=Bioethics |volume=23 |pages=433β440 |year=2009 |doi=10.1111/j.1467-8519.2008.00688.x |pmid=19077128 |url=http://www.astro-ecology.com/PDFLifeCenteredBioethics2009Paper.pdf |issue=8 |s2cid=25203457 |url-status=live |archive-url=https://web.archive.org/web/20121102064743/http://www.astro-ecology.com/PDFLifeCenteredBioethics2009Paper.pdf |archive-date=2 November 2012 }}</ref> Philosophical definitions of life have also been put forward, with similar difficulties on how to distinguish living things from the non-living.<ref name=Jeuken1975>{{cite journal|title=The biological and philosophical defitions of life |author=Jeuken M |journal=Acta Biotheoretica |volume=24 |issue=1β2 |pages=14β21 |year=1975 |doi=10.1007/BF01556737|pmid=811024 |s2cid=44573374 }}</ref> [[Legal death|Legal definitions]] of life have been debated, though these generally focus on the decision to declare a human dead, and the legal ramifications of this decision.<ref name=Capron1978>{{cite journal|title=Legal definition of death |author=Capron AM |journal=Annals of the New York Academy of Sciences |year=1978 |doi=10.1111/j.1749-6632.1978.tb50352.x |pmid=284746 |volume=315 |issue=1 |pages=349β362 |bibcode=1978NYASA.315..349C |s2cid=36535062 }}</ref> At least 123 definitions of life have been compiled.<ref name="JBSD-20110317">{{cite journal |last=Trifonov |first=Edward N. |title=Vocabulary of Definitions of Life Suggests a Definition |date=17 March 2011 |journal=Journal of Biomolecular Structure and Dynamics |volume=29 |issue=2 |pages=259β266 |doi=10.1080/073911011010524992 |pmid=21875147 |doi-access=free }}</ref> Summary: Please note that all contributions to Christianpedia may be edited, altered, or removed by other contributors. 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