Could Aliens Be Non-Carbon Based?

Animation of the structure of a section of DNA...

Post Author: Bill Pratt

The scientists at Reasons to Believe have always argued that finding advanced life on other planets is extremely improbable, considering the hundreds of conditions that must be simultaneously met for a planet to support advanced life.  Earth is quite unique in this regard.

When I’ve mentioned this to friends and family, they sometimes express skepticism and claim that maybe there are life forms that could exist with different chemistry than the carbon-based life on earth.

In an article published last year, Dr. Fazale Rana argued that non-carbon based life forms are just not feasible.  Rana explains:

Of the 112 known chemical elements, only carbon possesses sufficiently complex chemical behavior to sustain living systems.  Carbon readily assembles into stable molecules comprised of individual and fused rings and linear and branched chains. It forms single, double, and triple bonds. Carbon also strongly bonds with itself as well as with oxygen, nitrogen, sulfur, and hydrogen.

What about silicon?  This is the most common idea I hear.  Rana  replies:

Silicon belongs to the same chemical group as carbon and should display similar chemical properties, prompting some astrobiologists to propose that life could be based on this element. But while silicon does form rings and chains, these structures lack the stability and the range of complexity found in carbon-based compounds. Silicon-silicon bonds are much weaker than the corresponding carbon-carbon bonds, and unlike carbon-carbon bonds, they are susceptible to oxidation.

Silicon won’t work.  Then what about arsenic or phosphorus?  Rana explains:

Though arsenic and phosphorus share some chemical properties, the two elements display significantly different chemistries as well. Phosphorus is a nonmetal. Arsenic is a metalloid.  Phosphorus reacts with oxygen to form chemical compounds called phosphates. These groups take part in the linkages that constitute the backbone of the DNA molecule by reacting with the sugar, deoxyribose. The sugar-phosphate linkages are described as phosphate esters. Arsenic will also form a compound called arsenate by reacting with oxygen. Arsenates and phosphates display some chemical similarities, but esters formed with arsenates are unstable. They could never be used to construct the backbone of DNA––considered indispensable for life––or another similar compound.

The bottom line is that based on all the known chemical elements, scientists are fairly confident that advanced alien life would have to be carbon-based, which places severe limitations on the kinds of environments that our E.T. friends could live in.  Don’t hold your breath for an alien visitation any time soon.

12 thoughts on “Could Aliens Be Non-Carbon Based?”

  1. I’ve never understood the argument that the Christian story must depend on the unique place of Earth as a sole location for life. The only rational I can imagine is either that the Bible says nothing about such things, but then I can’t imagine why that means anything. The bible has silent about many things, I do not remember a specific reference to squirrels, yet I am assured they actually exist. The other possibility I can imagine is that such a creature would be outside the Christian story of redemption, or even our view of man as the pinnacle of creation. But what of that?

    The Bible only tells us of our story with God. It does not follow that there can be no other stories. Perhaps life elsewhere could be sub-rational, like fungus. Or they could be unfallen, or they could be ransomed by the work and person of Jesus, even though it did not happen on that planet. There is no problem with that, anymore than the fact that the incarnation happened on another continent, among a different people.

    The Bible is silent because, true or false, it isn’t germane to the story we are to hear.

  2. Hi Eric,
    I agree that the existence of alien life is not a Christian defeater. On the other hand, I do think that there is a lot of scientific evidence that the earth is truly unique in its ability to support human life. I seriously doubt that we will ever find advanced alien life, not because I think the Bible demands it, but because of the scientific evidence.

    God bless,

  3. I quite agree, but we’ve been fooled before! Once we thought that the chain of energy for life had to be solar based, that the chain of predation all went back to plants that got their energy from the sun.

    Now we are finding organisms that pull energy from all sorts of places, deep sea thermal vents come to mind. Who can tell what there could be?

    But I also think the chances are tiny, and that they shrink the more complicated the form you are talking about.

  4. I think I probably put the issue backwards.
    It is not that presence of non-terrestial life weakens the claims of Christianity, it is that the absence of such life supports it.

    Our faith has no problem if ET shows up. But if life is truely random, it is hard to imagine that rolling the dice billions of times across billions of years, a 7 only came up once.

  5. Bill, you say “I agree that the existence of alien life is not a Christian defeater.” Then why is this post relevant on a Christian apologetics board?

  6. Marv,
    The uniqueness of the earth to support human life is evidence for the design argument for God’s existence. If we did encounter advanced alien life, then this would weaken the design argument, but it would not nullify Christianity. In other words, one of the philosophical/scientific arguments for God’s existence (the modern design argument) would weaken, but there are a couple dozen more arguments that would still work. In addition, there is no Christian doctrine that takes a position on alien life.

  7. I have no idea. I did not find it in a peer-reviewed scientific journal. You are welcome to contact the author and ask him.

  8. First I’d like to say thank you to Bill Pratt for this site. I do really LOVE it. However, I was a little taken back as to this particle post. The main reason being, is that biblically, angels and all other heavenly host are most certainly, by definition, aliens. So aliens therefore most certainly do exist and humans have already encountered them.

  9. Do you think that perhaps “alliens” could be shorthand for “non-terrestrial life, of the same order as the organic life found here”?

    I think that would fit the popular understanding of the word, and would not violate the the sensible objections you raise.
    At least, that’s what I took him to mean.

  10. Hi Ariadne,
    This post was referring to physical life, not spiritual life. Angels are non-physical and so the laws of chemistry and physics do not apply to them.

    Merry Christmas!

Comments are closed.