• Question: Carbon is the element that underpins the majority of life's essential molecules, but why couldn't silicon do the job instead?

    Asked by to Aimee, Chris, Dave, Greig, Laurence on 19 Jun 2014. This question was also asked by .
    • Photo: Greig Cowan

      Greig Cowan answered on 19 Jun 2014:

      Good question! Silicon could maybe do the job, but it is a bit tricky for a few reasons:

      1. Silicon is much less abundant (by a factor 10) than carbon in the Universe. This makes it less likely to be available to be used for bio-molecules.

      2. Silicon is a larger atom than carbon. This makes it more difficult to form bonds with other atoms. Forming different types of bonds (single, double, triple) is one of the characteristic features of carbon and are what give it unique properties to be used for life.

      3. Silicon doesn’t make molecules with as many different types of other elements as carbon. This means the range of molecules that can be made is far fewer.

      All that being said, if the conditions were right on another planet, silicon could be used, as could other elements such as boron, or even metals!

      There are some good science-fiction books that discuss these sorts of issues.

    • Photo: Laurence Perreault Levasseur

      Laurence Perreault Levasseur answered on 19 Jun 2014:

      great question!!
      Greig is absolutely right! I’d just like to add a few reasons:

      – even when silicon does bind with other atoms to make molecules, those are usually very unstable and strongly react with water. It’s possible to make some stable molecules, but they look very different than just taking the carbon atoms out of a molecule and replacing it by silicon

      – long chains, which are essential to make things like protein, are even less stable (or, at least, we don’t understand how to make stable ones)

      So even if on Earth there is a LOT more silicone than there is carbon (by a ratio of 925:1), it was still easier for life to start out based on carbon. It’s possible, however, that in environment with very different conditions, like different pressures and temperatures, silicon plays a more important role in extra-terrestrial forms of life.

    • Photo: Aimee Hopper

      Aimee Hopper answered on 20 Jun 2014:

      If the conditions were right then I suppose it could – many people studying exoplanets look at silicon rich planets as possibilities for harbouring life.

      Just as a thought, if we completely replaced all carbon with silicon, then we would breathe out silicon dioxide, SiO2 instead of CO2. This is sand! :S

    • Photo: Dave Jones

      Dave Jones answered on 20 Jun 2014:

      Silicon could do the job! Just like all the other guys have said, Silicon is pretty similar to Carbon in that it is capable of forming very similar molecules and very similar bonds. There are some fundamental differences which would make it a little “worse” than Carbon which Greig and Laurence did a great job of explaining. But, still none of those reasons is so big that we don’t believe silicon-based life could exist, that’s why it’s not just something that you read about in sci-fi books but something which is actively discussed in the search for aliens and the study of planets around other stars!

Comments