Why Is All Life Carbon-Based?

Feb 16, 2013 By Sarah Charley
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You’ve probably heard the phrase “carbon based life” or “organic molecules” tossed around at some point in your life.  But what does “carbon based life” truly mean?  Are we really made out of that black charred stuff left over after a campfire, or the carbon (aka graphite) inside pencils?

The short answer is…yes!  Carbon atoms form the “backbone” of almost all the important biological molecules floating around in our bodies (except water, of course.)  Therefore, when we say life is “carbon based,” we mean that our skin, hair and cells are all made out of molecules that contain large amounts of carbon.

But what is carbon?

Carbon is an element, one of the 118 elements listed in the Periodic Table of Elements.  Everything we are familiar with -- you, me, the air, the ground, plants, animals, minerals -- are made up of atoms. 

There are 118 different types of atoms, but only a handful of these different types are actually important in our everyday lives.  In fact, about 97% of the human body is made out of only six elements — carbon, hydrogen, nitrogen, oxygen, phosphorous and sulfur, also nicknamed the “CHNOPS” elements.  The rest of the human body is an eclectic mixture of minerals and metals: calcium (in our bone and teeth), iron (in our blood), potassium, sodium, zinc etc.

But why carbon?

Let’s get to the true question here—why is life carbon based, and not based off of one of the other 118 elements?

Out of all the elements on the periodic table, carbon is arguably the best at bonding. Carbon loves bonding, and it is not picky about who it bonds with.  Carbon will bond with any of the “CHNOPS” elements, and it will bond with other weirder atoms, like zinc and iron. 

Oxygen and some of the other CHNOPS elements can form bonds as well. But what makes carbon unique is that it can bond with other carbon atoms to create long carbon chains and rings. No other element is capable of forming molecules as large and complex as carbon based molecules (think about it—without carbon chains and rings, there could be no DNA!)

Also, most carbon-based molecules are very stable and will not spontaneously fall apart. But they can also react to make new molecules. Our bodies need to be able to digest the compounds we consume (aka food) into small and simple tidbits, so that biological processes can then “click” and “snap” these tidbit back together into useful molecules. Carbon based molecules are strong enough that these small and simple tidbits will stay intact, allowing our body can arrange and rearrange them into useful molecules.

It is no wonder then that carbon-based molecules are the best suited to sustain life.  Life is complex; therefore, life molecules need to have the capability to be complex as well!

For more information, see my blog post on Inside NOVA: “Finding Life Beyond…Carbon?”