With the temperature, environmental and atmospheric requirements needed to systain life on earth falling into such narrow ranges, why do scientists believe that there may be life on other planets?

Truth is that the universe is a GIANT place to live. We (humans) live in the Milky Way galaxy, we live in a tiny solar system in the fringe of the Milky Way. We have discovered many stars that host a few planets and these planets may hold life. But to get to those planets we would need to host an expedition that is self-sustaining for hundreds of thousands of years. There are thousands of stars in our galaxy and thousands of galaxys in the universe. Some scientists believe that there are many more universes with nothing in between. Givebn these odds it sreems that there must be life SOMEWHERE else in the galaxy and indeed the universe. Unfortunatly the theory has not been proven, but we do have evidence that at one time there WAS life on another planet. The planet Mars scientists believe. A simple bacteria was found washed somewhere. Australia or Antarctica I believe.

Hope this helps.