This reminds me of my favorite "thought experiment" to poke at intuition: with no other information that what most people learn in elementary/middle school science (or what I would assume is taught, i.e. the water and respiration cycles), where does the majority of a tree's mass come from?<p>First we might look at dirt, but that doesn't quite pan out; where does the mass come from, and how would it be replenished? We don't see gaps slowly start forming around roots, and dirt doesn't just build up in other places, so that's probably not it.<p>Next we might look at water, but water is only made of hydrogen and oxygen, and the oxygen is released. The water also brings in nutrients, but there's no way it brings in enough to generate the majority of a trees mass.<p>So there's only one place left, which is never anyone's first guess and almost never crosses anyone's mind at first glance: <i>air</i>. It's around this point that most people realize that a majority of a tree is <i>carbon</i>, which all comes in from the air as carbon dioxide.