Life is a big coincidence
Its a long story to tell actually. You need to know how the earth was a million years ago; how life sign started showing up; and how they resulted into newer ones. The story goes on. Its like an endless saga. However I found the facts interesting. But I don't think a normal person can digest the facts, so well. Try this wikipedia page for a start. Click here. Its a long article, but take time to understand it.
Now that the fact that life has no explicit purpose is evident (or thats what we can conclude from the current scenario of investigations) we live as if there is some purpose. Why? The answer to this question can only come if we are keen on learning the details about our past.
I feel as if there is a whole ocean I have yet to swim through.