Ever wondered where a huge tree gets its weight from? Just like we grow from the food we eat, trees also have a source for their mass. But where does it come from? Is it the soil, the water, or maybe the air?

Long ago, people thought plants got their weight by taking in minerals from the soil. But in the 1630s, a scientist named Jan Baptist van Helmont did an experiment to find out.

He planted a small tree in a pot of soil and took care of it for five years, only giving it water. When he weighed the tree at the end, it had gained a lot of weight, but the soil had hardly changed. This showed that most of the tree’s weight didn’t come from the soil.

Van Helmont thought the tree got heavier by drinking water, but the real answer is something called photosynthesis – how plants make their food.

Plants use sunlight to mix carbon dioxide and water, making sugars and giving off oxygen. Leaves take in carbon dioxide and water, and the oxygen goes out. The carbon stays in the plant and becomes sugars.

Most of the stuff that makes plants big and strong comes from the carbon dioxide in the air. This process turns the carbon dioxide into a substance called cellulose, which builds a plant’s structure, like its trunk and stems.

So, almost all of a tree’s weight – around 95% – comes from the air. They grow using sunlight and carbon dioxide, making themselves out of the air around them. It’s pretty amazing how they turn something invisible into something as solid as a tree!