Given that this Blog is so new and I’ve only done 4 postings prior to this, I hadn’t imagined that I would be so quickly returning to the same topic- how we define the term “life.” But that definition, if there is one that everyone can agree on,is seminal to the discussion of the search for life elsewhere in the Universe and therefore is seminal to this Blog. So that’s my rationale for repeating myself and this is an ever evolving topic 🙂
While doing some research recently, I had the good fortune to come across a video presentation by Brother Guy Consalmagno , Planetary Scientist and Director of the Vatican Observatory, which was part of a University of Arizona lecture series on the scientific definition of life. It was worth investing an hour of my time to watch and I hope that you will do the same. It’s a fascinating perspective of all of the various world views and philosophies that have informed the definition of “life” over time, and which will no doubt continue to evolve and change in the future. Here is address:
Or just do what I do- google it:) But please watch it and if you can, come and join ( or start ) the conversation and tell me what you think. Because as Brother Guy so astutely summarizes near the end of the presentation: “Our knowledge will always be incomplete. That’s why we keep looking.”
Br. Guy takes us through a brief history of how life has been defined, scientifically and philosophically, over time. At one point, he tells us that there has been some 48 definitions–some lofty and rather crusty , such as the famed biologist and writer, T. H. Huxley’s 1848 definition of the “vital forces(presumably of life ) are molecular forces” —which I have to say— I don’t even know what it means! ( by the way, did you know that he created the term agnosticism to describe his own views? The things you learn when you do research:)
Our human view of what is”alive” has obviously evolved as we learn more about the vastly diverse life forms on our own planet. Br. Guy points out that even such logical assumptions as organisms needing light and warmth to live, have been challenged by the discovery of species that survive and “live” in perpetual darkness. My favourite illustration of how we limit ourselves by our human assumptions comes in BG’s reference to Gene Rodenberry, the sci fi genius and creator of Star Trek . Mr. Rodenberry apparently said that the aliens on Start Trek could looks bizarre and outlandish and be any colour of the rainbow, but they needed to have eyes for the audience to accept that they were living creatures. Which is –as Spock would say -fascinating! We now know that there are creatures on our planet who don’t have eyes and are very much “alive.”(the “star nosed mole” is one of my favourites that came up during my research ) . And so on…
I think that Br. Guy hits it out of the ballpark when he summarizes what I think is the heart and soul of this debate with this statement: “Our sense of what is living and what is needed to live is deeply imbedded in the culture in which we live.”
I couldn’t agree more but I wonder if that, by its very definition , is limiting our understanding of what constitutes life? For example , one of the criteria for exoplanet candidates to be considered habitable is for it to be in “the Goldilocks Zone” , as in close enough t its host star to get sufficient sunlight and warmth for liquid water to flow. But we already know of species on our own planet that don’t require light and can live in the cold. I’m reminded of the affectionate “debates” that I would have with some of my colleagues from the local Astronomy Club about the potential for life in our own solar system. This was always a fun exercise as the flaky English major ( me ) debated the science nerds.
“There can’t be life on Venus, Maureen. It’s too hot and there’s no water”…to which I would respond ..” That just means that it can’t support life as we know it…” As in human life. But perhaps there is another kind of life that doesn’t need water and light? Aren’t the possibilities endless?
As Dr. Charles Cockell, Professor of Astronomy and Physics, says in my Astrobiology textbook- seeing as we are very busy right now looking for other planets and signs of life on them, ” we can at least engage in a useful debate about what might mean by the term life” Yes indeed —so we’ll know it when we find it! 🙂
As I complete this post, I am chasing some very exciting news just released by the European Science Observatory: An earth like, rocky planet has been found orbiting the Goldilocks Zone of the star Proxima Centauri . That is the star closest to our sun and our solar system– a mere 4.242 light years from Earth! Which is, in the larger cosmic picture, —practically next door. This is big! I have a feeling that this debate is about to heat up. Please join the conversation:)