Having vented my fill yesterday (and everyone else's) about how hard I found it simply to get to the class at all, much less with the right chapter under my belt, I shall turn to the far more trivial matter of what actually went on in this class, and what I learned.
The class reviewed the components of good soil—minerals in various sizes (sand, silt, and clay) organic matter, air, and water. I was familiar with this, and with the importance of soil aggregates (clumps) that leave spaces within which air, water, and roots can move. For many people the shocker is that organic matter should comprise only 5-10% of the soil.
But for me it was the graph quite indicated that in an ideal soil fully half the volume is taken up by air and water. That's right: 25% each. If I'd learned that before, I'd forgotten it.