Similarly, it blows my mind that all trees are made of air, specifically the carbon in it. I used to think that the biomass must come from the soil, but reality is more interesting.
It's also kind of weird to think that soil, really, is just ground up "stuff" that used to be trees, plants, rocks, etc.
Kind of like how the vast majority of weight loss in animals happens via exhaling.
Weirder still is the realization that all the air is just trapped light.