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Photosynthesis

August 12, 2009

I remember reading an article last year about how most kids don’t every accurately understand how photosynthesis works, and how these kids grow into adults, and how these adults end up being the ones that make human society churn ever forward.

PhotosynthesisThe process is obviously quite complex, but the idea isn’t all that hard to grasp.  Everyone remembers that plants take in carbon dioxide and release oxygen, even if they don’t remember how.  The trouble comes when people are asked what else the process does.

How do plants grow?  Well, they root themselves into the soil, which they take nutrients from, and they need water and sunlight.  Then photosynthesis occurs.  One of the byproducts is oxygen, but how do the plants grow? The obvious, yet always overlooked answer, is that the gases are turned to solids.  When photosynthesis was explained to kids and then they were asked, Where does most of the mass in this tree come from?, they didn’t know—most of them said water and dirt, because these were the only things that would make sense.  Air to wood?  Impossible.

So the misunderstanding is in chemistry in physics, in the changing of states of matter.  People know that carbon in solid form can be black crap we burn as fuel, but to think that the same compound can be part of a gas—something that’s invisible, that might not even be there, ether—isn’t doable.  There is a cognitive block.

I find it helpful to think about the opposite; instead of thinking about how a tree is formed, think about how it is destroyed—or, more specifically, what happens when a tree is burned.  One of the most fascinating things about fire to me, beyond its simply mysterious nature, is that it is the very act of sublimation in front of our eyes.  And I don’t think most people realize this.  We know that if the wood gets hot enough it burns, there is smoke, and that there is ash and coal at the end of it all.

But ask someone, Is the mass of the ash and coal equal to that of the wood burned?, and it is very likely that their answer will be wrong.  “Uh, sure.  That’s weird.  I’ve never thought of that” is wrong.  More right is “Huh, no.  I’ve never thought of that,” but when asked to explain what accounts for the difference most people will not.

The answer is staring them right in the face: The remainder of the mass—that is, what isn’t left as ash and charcoal—is gas.  They saw it happening the whole time they watched the fire.  It was the flame.  It was the smoke.  It was the warmth.  It was the very air around them.

The misunderstanding is problematic.  If people never understand that what they destroy is not really destroyed, whether they are familiar with the Law of Conservation of Matter or not, they will never understand the impact they have simply by being alive.  I think this is why so many people have trouble understanding climate change; it’s not necessarily that they don’t believe as much as they don’t understand the processes that cause it. Large forests are called carbon sinks because they convert gaseous carbon into solids, matter that doesn’t trap heat in the atmosphere, matter that is incapable of contributing to the greenhouse effect.

And most people don’t understand this.  The forests are being cut down.  Cutting them down alone doesn’t always release considerable amounts of greenhouse gases into the atmosphere, because wood takes quite a while to decompose and in most societies the forests aren’t cut down simply to burn the trees anymore, but they won’t be sucking up excess carbon dioxide anymore.  No siry.

I like to think about what would happen if massive deforestation stopped.  Currently there is less forested land on the planet than there has been in a long, long time—maybe less than ever (ever not including the time before there were trees).  There is also more carbon dioxide in the atmosphere than there has been in a long, long time.  I like to think about leaving the forests alone, and then watching hundreds of millions of trees sprout up all around us, all over the world, and I like to think about all of that carbon being solidified.  It’s a nice thought.

I’ll just leave this here: The Man Who Planted Trees.

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