Answer:
I am essential to life on earth! I am split into thirds. Two thirds are the same. One of the thirds is 8. The other two are 1 each.
You cannot keep me until you have given me. What am I?
I have all the knowledge you have. But I am so small that I can fit into your hands. What am I?
Born in the ocean and white as snow. When I fall back to water I disappear without a trace.
I don't live within a house nor do I live without. Most will use me when they come in and again when they go out.
What do you purposefully put lots of in and on your body, but run away from when you encounter it outside?