Answer:
What has two legs but doesn't walk?
Until I am measured I am not known, Yet how you miss me when I have flown.
What zips through the sky with a tail of fire and dust. It could be an omen, its origin to discuss?
What is it which builds things up? Lays mountains low? Dries up lakes, and makes things grow? Cares not a whim about your passing? And is like few other things, because it is everlasting?
Salty water everywhere but not sea in sight.
You use it between your head and your toes, the more it works the thinner it grows.