Did you know that were there no moon, or if the moon we have were not the size it is, life would not exist on the earth?
You probably knew that were there no water life would not exist, but do you know that water is necessary for life in a multitude of ways having nothing to do with hydrating our bodies?
Biochemist Michael Denton summarizes a few of the ways in which all of these factors are necessary for life and why at least some scientists think that planets that can support life might prove to be extremely rare in the cosmos in an article at Evolution News and Views. Life requires so many properties of a planet to be just right that the earth is sometimes referred to as a Goldilocks planet, because it meets all of these requirements.
The article is not long and it's very informative. Denton is the author of the book Nature's Destiny which goes into a lot more detail on the myriad ways the earth and the chemical properties of carbon, water, and oxygen are so ideally suited for life. Were the properties of these substances different from what they are in any number of very minor ways life simply could not exist.
The post at the link is good. The book is great.