As I understand it, plate tectonics wasn't really confirmed until the early 60s. Biggest obstacle was that Wegener didn't have a good proposal for how the plates moved (another obstacle was the act of ignoring the hypothesis). He thought the continents kind of moved like icebreakers plowing through the oceanic crust. Granted, the rest of his evidence was fairly spot-on.
Anyhow, it was explained to me in elementary school, but I was born in 87.
So I'm listening to the interview. And it seems that Niel is saying that long ago, when the planet formed, lighter density rocks floated to the surface.
Which, of course, is true. But this means that there would be an essentially even distribution of granitic rock across the surface of the earth. The earth certainly does not have that today, with mountainous regions having a crust at least twice as thick as that of continental crust on average (itself thicker on average than oceanic crust).
Now why would that be? How could that happen? Oh, gee, I don't know, maybe collision? Since granitic rock doesn't really subduct, it crumples and a divergent zone is produced elsewhere. This produces oceanic crust.
What's so difficult about that? Granted, I have quite the simple model, but still.
The mid-atlantic ridge is a divergent plate boundary. No subduction occurs there.
If you want to see subduction, I recommend looking at the Juan de Fuca plate. It is currently being subducted underneath the Cascades and should eventually vanish if plate tectonics is right. Of course, we'll have to wait a very long time for it to completely vanish, but in the meantime it should be possible to measure how much it is shrinking.
And yeah, video of it happening isn't exactly possible.
[abe: adminmoose was putting up his warning as I posted this. sorry about that.]