Where does a tree’s wood come from?
A big oak tree can weigh many tonnes. Most people guess its mass comes from the soil, but the soil under a tree hardly goes down at all. Most of it comes out of thin air! Leaves take in carbon dioxide and, using the energy in light, join it with water to make glucose, which the tree then builds into wood.
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About 400 years ago, Jan van Helmont grew a willow in a pot of weighed soil for five years. The tree gained about 74 kg; the soil lost only about 60 g. He thought it was all from the water he gave it. We now know most of it came from carbon dioxide in the air.
by calcali