What Am I Riddles

Question: You put me on a table and cut me, but you don't eat me.

What am I?

Question: The more of me you have, the longer your life.
The more of me you have, the less you have left.

What am I?

Question: What goes up when the rain goes down?

Question: What always eats but is always hungry?

Question: What is as ancient as the earth but new every month?