This has got to be the end! I just write these in regurgitated lumps and send them off right away, tear them off the typewriter and throw them at the copy boy. :)
The thing that is missing from the continent collision picture is the whole context. This is happening when continents are lumping together, and the super-continental mass becomes a big thermal insulator. There is a conjecture (that I like) that the inner core is a big fission reactor, and that heat has to go out. Anyway, there's lots of heat from something. These collisions find themselves in the middle of the super-lump, and really heat up. It's also where they split again.
It's at the middle of these super-lumps that the Large Carbon Cycle comes back at us to some degree. If we have a really big lump, we get the Mesozoic, when all that co2 and water vapour was injected into the air.
Did I mention how great an insulator water vapour is? That's because it totally breaks up the atmospheric convection cells. Remember, three ways to get rid of heat - conduction (not applicable to air), radiation, and convection. The last is orders of magnitude more effective. You don't leave a big lump of air in your attic to act as an insulator, it's useless because of convection. You put in fiberglass, which has cells of air too tiny for convection.
So water vapour in the air rises until it starts to condense and fall. This kills the convection, as you can tell when you fly over a perfectly flat cloud bank and sip your full coffee cup. To punch through, that takes a monster thunderstorm (don't drink coffee in that).
So in the Mesozoic, water vapour made it warm, and an incredible amount of co2 made the plants go ballistic. Dinosaurs loved it, large mammals died because of heat stroke. We'd only visit in an air-conditioned time machine. Giant carbon beds were laid down (coal).
But thank goodness only a teeny bit of that carbon was released. The rest stayed down below, got super-hot and floated us until the next big collision. What is really down there? Like the mythical nuclear reactor, we may never know. But I think there is an incredible amount of hot, pressurized carbon. We're floating on a bed of diamonds!
That's all folks!
ps. whoops, I was so proud that my sudden conclusion was better than a nuclear reactor at the core, that I forget the question of how plants existed before Man came along. There is always some co2 leaking out along the rift valleys and such, and the volcanic subduction zones. This causes a net plant growth which is good for sediments.