Logic Riddles

Question: People see through me, but none pass through without killing me. I can be anywhere, and can be seen double or single. What am I?

Question: Waking up I see a smile as warm as fire. Sleeping I see a gaze as cold as ice.

Question: Which triangle will have a larger perimeter : 3,4,5 or 3,4,7 ?

Question: What gets broken without being held?

Question: What is 5,000 years old and still turning?