• Question: if life on other planets was sophisticated like humanity, could the aliens depend on other substances to live (e.g., not oxygen, water, ETC)?

    Asked by superkingtom to Aled, Ellie, Kev, Willem on 19 Mar 2014.
    • Photo: Kevin Arbuckle

      Kevin Arbuckle answered on 19 Mar 2014:


      The short (and probably also the long) answer is that we have no way of knowing. Because alien life is probably very different from us in many ways we can’t be certain what they need to live. We can think of what conditions life can survive on Earth and see where those exist in the solar system or further afield (and people have), but since all life on Earth evolved from one common ancestor and alien life would not be a descendent of that ancestor there are still similarities amongst all life on Earth that might not be similar to aliens.

      Hope that makes sense!

    • Photo: Aled Roberts

      Aled Roberts answered on 19 Mar 2014:


      Hey Superkingtom!

      It is my personal opinion that any life on other planets might arise from the use of “other” substances! It is quite possible for them to use something other than oxygen and water IF they have evolved to do so…

      However we should bare this in mind… There are two very good reasons why our attention is so strongly focused on water for life. First, it’s an efficient solvent for biological chemistry, allowing molecules to move around in cells, and it has properties that are friendly to life β€” a high heat capacity, the ability to remain in liquid form across a wide temperature range and a molecular density that forces molecules to organize themselves, rather than the water organizing around the molecules. Secondly, the biosignatures of a water-based chemistry are a lot easier for us to identify remotely.

      However focus has turned to the use of methane instead of water by “aliens”… On Titan, where the temperature is just minus 179 degrees Celsius, water is as solid as rock and liquid methane runs through the river valleys and into the high-latitude polar lakes. Instead of a water cycle, Titan has a methane cycle, and a complex molecular soup formed from reactions in the upper atmosphere between ultraviolet radiation from the sun and methane. It is possible that life could have evolved to use this instead of water… Therefore what we perceive as a habitable zone of life could be different depending on what we need… creating lots of new places to look for life!

      But as Kev said… We have no way of knowing… Therefore we best look in our own habitable zones as we know life evolved here! (as we are alive!) πŸ™‚

      Hope that helps πŸ™‚ Don’t forget to vote!

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