That was a bit of a revelation too in that the top 100 km or so of the mantle is just as strong as the crust and is joined to the crust to make a single 'mechanical layer'. Interesting stuff!
Third eye opener concerned the next layer down, that of the lower mantle. This layer it turns out while not rigid, is neverhteless solid and yet slowly circulates at a rate of a few centimetres per year. Now this is a difficult concept to grasp but a good analogy is to compare the rock of the lower mantle with say, a slab of Devon toffee! Okay, a bit bizarre, but stay with me okay? Now, put the slab in the fridge for a while and it will be hard enough to shatter if whalloped with a hammer. Go on try it if you've got a spare slab lying around! However, if you leave another slab in the fridge with slightly less than half its length overhanging the fridge shelf and leave it for a few months, it will eventually bend over the shelf. Okay, I've not actually tried this myself - there's little or no chance for a slab of toffee surviving for long enough in my house antway, but I'm told it does work! Anyway, my point is that, yes the toffee is obviously solid, but will still bend if given sufficient time. So it is with the rock that makes up the lower mantle which is subject to what is called 'solid state convection'.
And all this is even before the course (or 'module' as the OU now like to call them) officially starts on Saturday 13th! And I haven't even mentioned 'cowpat bombs' yet!?! Maybe next time dear friends!
Cheers for now!