Dont' ask me why the writing has to be centered. Getting to the point now, humanity has lived through the stone age(which really went from like four million years ago with the Australopithacines) to the bronz age of what three thousand B.C.? Then there was the iron age around a thousand B.C. Each period took less time to get to the next I think. This is interesting in the light of the nanotube era we are in now(the video above is proof of this); how long till the next materials revolution? Think decades if not years! As soon as nanomanufacturing gets going, we'll take the next step beyond the nanotube era!