At the risk of embarrassing myself, I’ll share a confession.

For context, I took five years of Latin: four in high school and one in college. In addition to learning the language, all my Latin classes taught a lot about Roman history. Emperors, internal politics, Caesar, etc. I was always learning some random bag of facts about Roman history. In high school, I won the award for top Latin student in my graduating class. So I wasn’t a bad Latin student.

Here’s the confession: I somehow don’t even vaguely remember the rough timespan the Roman Empire existed. Maybe Jesus time? I know he was killed by the Romans (is that right?). Were they around for a long time after? A long time before that? When was Romulus and Remus allegedly fighting? Virgil wrote the Aeneid when? I don’t have a clue. Despite being a kind of “Latin expert” I am missing a much more important foundational fact: when all of this was happening.

When I say trees are made out of air I’m not talking about the fact that there is a lot of empty space inside a tree (or actually anything made out of atoms). I mean something more mind-blowing.

Imagine you are holding a piece of dry wood. Where did that wood come from? A tree. Okay sure, but what are you actually holding? Where did the tree get that stuff? It turns out that almost all of the mass in dry wood comes from the in the air. This follows from a simple fact about how photosynthesis works:

The carbon and the oxygen in the glucose () come from the and the hydrogen comes from the water. Since hydrogen is the lightest atom in the universe, it adds almost no mass, so nearly all the mass of glucose traces back to the . Wood is mostly built from glucose, so by mass, a dead tree^[1] is mostly the carbon and oxygen that came out of the air.

It’s kind of unintuitive. Wood is hard and stiff and air is not even close to either of those things. But if you are a biologist or know some basic chemistry you would think that this is the kind of obvious thing you would want to know. At the very least you would expect the best math and science students in the world to be familiar with such basic biology. But take a look at this video of a documentary film crew asking MIT graduates where they think wood comes from:

One student, upon being told that most of the mass in the wood comes from and not the dirt in the ground, s...

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