Answer:
I am the greatest teacher out of them all, but alas in the end I kill my pupils.
This thing all things devours: Birds, beasts, trees, flowers; Gnaws iron, bites steel; Grinds hard stones to meal; Slays king, ruins town, And beats high mountains down.
What has wings, but can not fly. Is enclosed, but can outside also lie. Can open itself up, or close itself away. Is the place of kings and queens and doggerel of every means. What is it upon which I stand? Which can lead us to different lands.
In many years, not much has happened. In many minutes, a lot has happened. In one second, everything has happened.
What turns everything around but does not move?
I have two eyes in the front and a lot of eyes on my tail