My son, bless his soul, believes that I am much better than I actually am at decorating. Anyhoo... he volunteered me to do a cake for his 6th grade science class showing the earth's core, continental plates and at least two continents. Someone please help me !
OMG that sounds really neat!! Check out this spectacular watermelon cake I just saw by Edibleart http://www.cakecentral.com/modules.php?name=gallery&file=displayimage&pid=1270933 for an idea about doing the earth's core: sports ball pan with a wedge cut out (like the watermelon) but then of course you need to pop a little ball-sized core in there (cake, RKT, whatever).
Continental plates, ok you've got me on that one, they are so big it will be hard to get templates to conform to a sphere (then again you might be able to find something online, you can find anything online, right?!). I'd probably try to buy/borrow a science globe showing the tectonic plates, and try to copy them by sight. Well if I could pipe that is lol.
Continents...well, if you can get those tectonics down I suppose the continents shouldn't be too hard. Choose the smallest ones haha. If you cut them out flat in fondant it would be easy to shape them onto the globe, (I would think doing this for the plates would be darn near impossible due to the curvature and the fact that the plates must fit together like puzzle pieces.) Or just pipe on the general shapes.
There are two pages of "earth" cakes in the galleries you could use as a reference. Quite a few of them are spherical in shape. Good luck!
I think a cutaway is the way to go, too. But the plates - yeah that will be tricky.