Why Are We Here

I've been doing a lot of thinking lately and I don't know why humans are here on Earth...  Thoughts like, are we the only ones?  Who created us?  If God created us where did he come from?  Why is Earth the only known planet that can inhabit humans? Consume my mind day and night.  It may not seem like a very important thought, but really, it is our entire being.  What's more important than that?  I don't know...  Maybe it doesn't matter and I should just not worry about it.  Maybe it is just a nagging thought that won't escape my trembling thoughts.  Maybe I should just leave it be and live.  Maybe...