What am I?

I am necessary for all living things, but I can also destroy life. What am I? See answer »

My first letter is in WEAR but not in ARE. ____
My second is in PRAY but not in PRY. ____
My third is in RACKET but not in CREAK. ____
My fourth is in ALIVE but not in VIAL. ____
My fifth is in BIRDS but not in BIDS. ____