Could Aliens Really Exist?

Hello! As the title suggests, I am doing an investigation about life on other planets, extremophile for instance. I might need to talk about how life can survive on earth but not the others; even if life does exist on other planets, what kind of conditions do they need etc. My question are:

  1. How can I structure this report and show the link between my explanations?

  2. Where can I get those resources? Can someone please suggest me a few sites to start with?

Much appreciated