On Google+, Bob, K0NR posted,
Interesting question from a 10-year-old student in the ham radio class today: Why do we always talk about the D, E and F layers of the ionosphere…are there A, B or C layers? I don’t know the answer to that one.
Now, I’d always heard that the reason the lowest layer is the D layer is because when scientists first started studying the ionosphere, they found these three layers and postulated that they would find three layers below them, i.e. the A, B, and C layers. They did not find them, but never went back and relabeled ones that they did find.
I posted this as a reply, and Bob asked if I had a reference. Well, I Googled all over for one, but came up empty. Do any of you know if this explanation is true, or if this is a ham radio urban legend?