Why On Earth?

Why on earth?  Oh boy! Another existential question from me.  I was watching a Nova show on PBS about planets and stars.  Really not many updates from what has been known for awhile except the fantastic images and data from Mars.

Blue Marble 2012 - NASA image

But that thought - why on earth? - occurred to me.  We have life because of water.  Scientists are looking for existence of water on other planets, and think they found that Mars used to have it. 

But that doesn’t mean that their life forms were like ours.  Why on earth (oh there it is again!) is our planet the only one with us on it?  Why human beings?  And supposedly we’re evolving, getting smarter, making huge advances in technology, science, money-making, etc.  And over-populating while we’re at it.  Crowding out animals from their habitats, depleting people of basic needs: air, food, water.  Water.

More water flows as the polar caps melt, but not more in a good way.  Oceans rising, average climate temperatures increasing, creating more problems.  And the water - will it just evaporate from the increasing heat - dissipate?  Despite the melting will we have a shortage of water that isn’t sea-water, isn’t potable?

earth's atmospheric layers - image NASA-JSC

Will there be a turning point hundreds of years from now (or sooner) where this planet has had enough of us human beings and finally gets rid of us?  Life on earth will be fine without humans.  Really.  Why on earth are we needed here to begin with?  To each his/her own answer is within.
Theresa M