Answer:
I am the word that is always spelled correctly by everyone.
I am black and white and full of fuzz
I am lighter than air but a hundred people cannot lift me. Careful! I am fragile!
I am longer than a decade and shorter than a millennium
I help you carry your books.
You can always see it, but it's too far away to touch. Mountains rest on it, and at sea it surrounds you. What is it?