It is Possible that intelligent life existed on Earth before and we just don't know it. Maybe some dinosaurs were sentient and went extinct via some dinosaur-caused disaster?
Seriously? Life exists because it exists, I think. Certain conditions occurred and one thing led to another. To ponder "why" creates all the sturm und drang of religion and questioning "the meaning", and all the rest.
I don't wonder "why" much, myself, since I am sorta convinced there is no answer. I do wonder HOW, though.
And I am fairly sure that life exists elsewhere, since in the vastness of the universe there must be other objects where life can begin. Will it be "intelligent" life? Or just a huge pile of algae? Who knows?
All my life I've been hoping for "contact", but I am beginning to accept that is unlikely. The obstacles are huge. Notice I said "unlikely", not impossible.
For some time I have been mulling over a story about "first contact" but I haven't got very far yet. What an interesting day it will be, though! Whenever and wherever it takes place...............