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NASAofficials harbinger March 12 that ancient Mars could have corroborate primitive liveliness . But this begs the question : What exactly constitute life ?
Merriam-Webster.com defines sprightliness as " an organismal United States Department of State characterized by electrical capacity for metamorphosis , development , reaction to stimulation and procreation . " But there ’s no individual satisfactorydefinition of life .
What is life? Defining the phenomenon is a challenge.
" I call back it is a mistake to attempt to define life , because we have only one example of life story , familiar life on Earth , and we have reason to believe that this example may be unrepresentative of animation in cosmopolitan , " Carol Cleland , a philosopher of science at the University of Colorado , Boulder , tell LiveScience in an email .
Defining life
Aristotle made the first attack at a definition , describing life as something that grow , maintains itself and reproduces . But this definition would exclude scuff , which are uninventive , while including affair like flame .
bid life sentence something that has ametabolism , the ability to take in energy to mature or move and excrete waste , is no unspoiled either ; cars do this , for example .
In 1944 , the physicist Erwin Schrödinger gave liveliness a definition based on the second law of thermodynamics , which states that the entropy , or disorder , of a closed in system increase over time . Schrödinger define animation as something that decreases or maintains its entropy . Yet this definition stops as it includes crystals , which resist entropy by forming highly structured lattices .
Trying to define life by its qualities is the awry coming , Cleland said . As an deterrent example , she cites scientist ' other attempts to delimitate pee in terms of properties like being wet , sheer and a good solution . " We did n’t ' define’water as H2O , but rather discovered , in the linguistic context of molecular hypothesis , that it is a chemical substance composed mostly of H2O molecules , " Cleland said .
Life on Earth is typically divide into two main chemical group : the cellular life flesh , which let in archaea , bacteria and eukarya ( all the industrial plant and animals ) , and non - cellular spirit forms , like viruses . Whether virus , which can replicate only inside the electric cell of a host being , count as " biography " is deliberate .
Life in the universe
Finding an airtight definition for life may not be so important , astrobiologist Chris McKay of NASA ’s Ames Research Center in California wrote in an email to LiveScience . It ’s " much better to have an idea of what life is built of , " McKay said . " life history is built of complex , constituent mote . "
Characterizing life is vital for identify it elsewhere in the universe , a possible action now beyond the kingdom of skill fabrication . McKay said that if life exists somewhere else , it would be a fabric system develop through reproduction , mutation and lifelike selection . [ 9 Exoplanets That Could Host Alien Life ]
Beyond Earth , one of the first billet humanity have seek tofind life is Mars . The Viking Mission in the seventies looked for grounds of life in the Martian grime . One experiment appeared to find grounds of metabolic reactions , but these were dismiss as fare from a non - living root ( though some still argue those results ) .
With the proclamation that NASA ’s Curiosity rover has come up evidence thatlife could have once existed on Mars , Curiosity has answer the interrogation it position out to canvas in November 2011 . The determination comes just seven month after the rover landed on the Red Planet on Aug. 5 , 2012 .
grant that Mars could have supported sprightliness , McKay said , " Now we call for to look for it . "
