What evidence could you use to support that the organisms you observed under the microscope today were living organisms?

Here is the question: What was the likely source of the raw material incorporated into the first life forms? I believe it is carbon, but I don't know why it is carbon. What I mean is, why is carbon considered the thing that makes something alive? Why are eukaryotes and prokaryotes simply considered alive just because they have carbon. Would that mean that carbon is alive because carbon has carbon? I would appreciate an anwser because I'm really trying to understand everything I run across. I love educating myself and I'm on a quest for knowledge. Thanks guys!

All the organism on your campus make up?

For a long time, it was believed that life originated from decaying matter. What is this theory known as? Name the scientist who experimentally disproved this theory.