The Veritasium YouTube video was fascinating.
In the video, people interviewed on the street were asked to say where trees get the stuff what makes the massive trunks and branches.
Trees can be enormous: according to livescience.com, the heaviest living tree on the planet, a giant sequoia named “General Sherman,” weighs 2.7 million pounds and has a volume of 52,500 cubic feet.
That’s a lot of material.
Where do you think all that material comes from?
The people interviewed had guesses -- mainly “from the soil” and “from the water,” and “from the sun.” Quite understandable, since the tree has roots that grow into the soil, and trees need water and sunlight to grow.
However, if the tree took enough stuff from the ground to build the tree, wouldn’t there be a tree-sized hole in the ground? And how could liquid water become solid tree? …how could energy become matter?
Soil, water, and sun are part of the story, but not all of it.
In grade school most of us learned plants harness sunlight energy to combine carbon, oxygen, and hydrogen -- “photosynthesis.”
The oxygen and hydrogen atoms are separated from water molecules that were drawn up from the soil through the roots and vessels to the plant’s factories -- the leaves. Some necessary trace parts, such as nitrogen, is carried up to the factories with the water.
There’s the soil and water.
Here’s the sun: During photosynthesis the plant uses the energy from the sun to combine the carbon, oxygen, and hydrogen to make carbohydrates -- food/building material. That process gives off a little leftover oxygen as well.
(It’s not quite that simple, of course: plants also use oxygen and they give off carbon dioxide, though mostly when they’re not photosynthesizing. But when photosynthesis is underway, they need more carbon dioxide than they produce and they give off more oxygen than they use.)
That system is all important to us animals: carbon dioxide is a waste material we breathe out, and we need to breathe in oxygen. The ultimate sweet trade.
So, back to the question of where the stuff trees are made of comes from.
In general, living plants are mostly water -- about 50% water for many trees, but up to 95% water in some plants. Take out the fluid water, as in dry wood, and most of what’s left of a plant is carbon.
What might be overlooked is that the carbon comes from carbon dioxide in the air, entering the plant’s leaves through special pores.
Turns out, the stuff that makes plants is mostly air and water, with essential nutrients from the soil helping the process.
Trees build wood to grow tall to lift their food factories (the leaves) high in the sunshine -- the ultimate energy source. In the end, according to the University of Illinois Extension Service, about half the mass of a living tree is derived from the air and about half the mass of a living tree is derived from the water, plus traces of soil.
Snagging carbon out of thin air is why plants sequester (take in and store) airborne carbon; trees are particularly good at sequestering carbon because they’re big and they live a long time. The Center for Urban Forest Research (a branch of the U.S. Forest Service), estimates the average tree can sequester about 88 pounds of atmospheric carbon each year, turning airborne carbon into wood and other parts of the tree.
Using sunshine to build yourself out of air and water, and not much more, is pretty remarkable.