Is a big tree made mostly out of air?

Have you ever pressed your hand against the bark of a big old tree? It feels rough, hard and solid under your fingers. A trunk like that can weigh as much as a few cars.

Yet that giant trunk started as a tiny seed you could hold on your fingertip. So where did all that wood come from? Could a big tree really be made mostly out of air?

The air all around you holds an invisible gas called carbon dioxide, which is a gas you breathe out too. A tree needs this gas, because it makes its food from it.

Each leaf has tiny holes on its underside, far too small for your eyes to see. The leaf opens these holes so carbon dioxide can drift right inside. A big tree has thousands and thousands of leaves, all catching air at once.

A leaf needs one more thing to build with, and that is water. The roots drink water from the ground. Then the tree pulls it up through the trunk and branches, all the way to the leaves.

Now the leaf holds carbon dioxide and water, and the sun shines down on it. Sunlight gives the leaf the power to join them together into sugar, a sweet food for the tree. What do you think the tree builds with all that sugar?

The tree sends the sugar down through its branches and trunk and turns it into new wood. Each year it adds a fresh layer of wood just under the bark. That is how the trunk grows wider and wider.

When you add it all up, most of the wood itself was built from carbon dioxide that floated in through the leaves. Water adds a smaller part, and the soil gives only a tiny pinch. So the hard wood under your hand is built mostly from air.

Carbon dioxide. Yes, the wood of a big tree is made mostly out of air, because its leaves catch carbon dioxide from the air and use sunlight and water to build it into wood.

Next time you touch a tall tree, you can smile, knowing you are touching air that its leaves turned into wood.