In the galaxy carbon is on 4th place (after hydrogen, helium and oxygen) In Earth crust it has respectable 15th place. Hydrogen, helium, neon - they are on to the top galaxy popularity list, but are too light to be kept by our planet in proportional amount. Quite a few elements in earth crust (oxygen, silica, iron) have roughly the place that one would expect from their galaxy prevalence. However, carbon does not follow this logic. Why it is so rare on Earth comparing its prevalence in other places?