On Earth life has six fundamental building blocks for life with them being Hydrogen, Carbon, Nitrogen, Oxygen, Phosphorus, and Sulfur. (1) Those elements of help make up more complex life through amino acids, proteins, nucleic acids / DNA, along with a lot of other things. (2) (3)

Though when it comes to the possibility of extraterrestrial life and xenobiology some individuals like to explore the idea that not all life has to use the exact same forms of life found on Earth. Most popular of which seems to be finding alternatives for Carbon and solvents. (4) (5) (6)

Now when I looked through this all it seemed like the possible forms of alternate life had little bounds for having something in common. Carbon based could be replaced with Silicon or Boron-Nitrogen, Phosphorus replaced by Arsenic, water replaced with ammonia, and so on with varying degrees of possibility. The only thing that cannot be replaced it seems is the need for Nitrogen.

At first I foolishly thought that like Carbon being replaced with Silicon or Phosphorus being replaced with Arsenic one could just use the same idea with Nitrogen. The problem is below Nitrogen is Phosphorus, already being used for the building blocks of life. I tried to think of a way that Phosphorus could just replace Nitrogen completely somehow and do the almost same job, though learning from the objections to Silicon based life just because elements share the same family does not mean they can replace each other.

So that left me rather stuck, as we understand how life works right now, is all life in the universe bound to have to use Nitrogen in some way or another? Or have I completely messed up, missed something, and dealing with a case of Nitrogen chauvinism?

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    $\begingroup$ From chemical standpoint, it's not too difficult to imagine a set of organic molecules that don't include nitrogen. However, from what we know about planets, it's difficult to imagine a planet where all other elements are present, but nitrogen is very rare. $\endgroup$
    – Alexander
    Commented Oct 11, 2017 at 17:54
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    $\begingroup$ Consider that your "nitrogen chauvinism" may simply be part of a 'bell curve' representation that describes both prevalence of an element and its ability to react with other elements. While helium is very common, its is essentially inert. Phosphorus on the other hand is far less common, but highly reactive, and at a wide variety of temperatures and conditions. I suggest that Nitrogen is a kind of 'crossroads' of the elements, light enough to be common, reactive enough to be in thousands (or more) molecules. $\endgroup$
    – Joe
    Commented Oct 11, 2017 at 18:23
  • $\begingroup$ @Alexander Yeah, I suppose my question should have been more along the lines of what could possibly replace Nitrogen. I understand the problem that Nitrogen is just the best. Though would you know what that set of organic molecules would use in place of Nitrogen if environmental factors were not limiting? $\endgroup$ Commented Oct 11, 2017 at 18:59
  • $\begingroup$ I don't think you are messing up as this is not a simple subject but I think a clearer understanding of the distinction of elements and molecular componds would help. It is hard to get away from nitrogen because it probably one of the top 10 most common elements but is possible to have amino acid analog without an amino (N-containing) group. ref: en.wikipedia.org/wiki/Abundance_of_the_chemical_elements $\endgroup$
    – P Chapman
    Commented Oct 11, 2017 at 20:10
  • $\begingroup$ "is all life in the universe bound to have to use Nitrogen in some way or another?" This is probably true for life as we know it. But there are much more exotic processes in the universe that could be alive and we'd never know because we don't have any frame of reference for them. $\endgroup$ Commented Oct 11, 2017 at 21:53

2 Answers 2


First, There are no known organisms whose DNA are composed with silicon or boron-Nitrogen or arsenic. These are theoretical possibilities based on the assumption that these elements/compounds can be substituted for their equivalent in the DNA Model. We don't know for sure that these substitutions can even work, because as you mentioned, just because two elements share the same family and ionic charge does not mean that resulting compounds will share the same properties.

Currently, Arsenic can end up in our DNA, when this happens it actually causes damage. This is how arsenic kills.

What the previous approaches all have in common is they all try to modify the current DNA Model.

All DNA is, is a means to store information that governs the construction and operation of a cell.

So to start answering your question:

Create an alternative DNA model that has 4 non-nitrogen compounds (in place of the amino acids), that can be used to organically synthesize proteins(or compounds similar to).

Obviously, this is a much greater effort than picking similar ions to swap out in the current DNA Model but its more realistic as you avoid the unproven property deficit.

Further rationality:

All life as we know it uses DNA, but all life as we know it exists on Earth. If we found extraterrestrial life on an extra-solar planet that used DNA that would lend credibility to Panspermia. Conversely, if we didn't that would mean life as we know it potentially did evolve independently on Earth. This is why it is foolish to assume that extra-terrestrial life will conform to the same genetic model we do.

  • $\begingroup$ Its sort of a cop out answer, however you are trying to change a variable of a complex and elegant equation, I'm just saying, change the equation. $\endgroup$
    – anon
    Commented Oct 12, 2017 at 13:59
  • $\begingroup$ Well I would rather have a nice cop out answer than no answer at all. Least it lets me know that there was no easy to find paper or something on the internet about theoretically replacing Nitrogen like Carbon. Though now I guess I will have to start stop thinking narrowly. $\endgroup$ Commented Oct 12, 2017 at 18:12

The honest answer is we don’t know because we have only one example biosphere to go on, that being Earth's. But we can make some educated guesses.

Firstly a few points should be noted. Nitrogen is one of the lighter elements, its more easily formed in stars than the heavier elements and it’s believed to be a relatively common element. So it’s unlikely that a world would exist without any.

Although it’s true that chemicals within the same column of the periodic table show many similarities, as you have already pointed out one element is not replaceable by another as increasing atomic weight (among other things) has a very profound effect on properties. Silicon does form many complex compounds showing properties in some ways similar to carbon, but its abilities are a pale shadow of the enormous multitude of compounds possible with carbon.

Also compare the relatively benign ammonia with its nightmarish brother borane (or more strictly diborane as borane molecules unlike ammonia have a tendency to dimerise to form B2H6) which is spontaneously flammable on contact with air and contains unusual B-H-B triple atom bonds.

So to answer your question I would suggest yes other life in the universe probably does use Nitrogen because it is so abundant. However if nitrogen was not present for any reason I would think that there is sufficient reactivity and complexity to be had with the other elements to create an alternative biosphere without it. In this case the many different nitrogen compounds in nature would be replaced by an array of different chemicals, not necessarily by those of a single element.

  • $\begingroup$ An array of different chemicals, huh. Thank you for that idea, gives me some more things to look up now. $\endgroup$ Commented Oct 12, 2017 at 18:17

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