What Am I Riddles

Question: I am a cave full of bones,
and the house of a worm.

What am I?

Question: You will see me every night sometimes i am scary and sometimes not What am I

Question: We have what we did not find; what we did find we left behind.

[What do we have?]

Question: Occurring once in a hundred years and once in thousands. But never in a day or a year or a century.

Question: Name two different words using following words only... 1. Without me 60% living beinga cant survive.. 2. Without me none ( living+non-living cant survive... 3. Both have five letters each but both r anagrams of each other..