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.
I am a kind of coat that can only be put on when wet. What am I?
I am the thing that is used to make your weight. What am I?
I have a head tail but no arms and legs.
The more you have me the less you see. Shine a light on me and I shall flee.
Whoever made me don't want me. Whoever bought me don't need me. Whoever use me don't know me.