What Am I Riddles

Question: My thickness is no more than a few centimeters, yet my depth can span to infinity. Although mundane, I intimidate most animals. When in my presence, you will inevitably follow me. What am I?

Question: What is big, has 4 feet, and can fly?

Question: Tear one off and scratch my head. What once was red is black instead. What am I?

Question: What cannot be seen or felt, but can only be broken by voice?

Question: I am around everything, everything that lives because of me. What am I?