I can be traced back to 3000bc, often go unnoticed, can be overhead, under feet or somewhere in between, evolution has changed me, am lighter than I used to be, and can protect your investment.

Answer 1

I would ask for another science teacher, this is not science. You deserve a quality education if you are paying for it. Teachers who give these to you as course work are wasting your time, in my opinion.

Answer 2

Helium