I find it amusing, bordering on cute, when atheists are saddled with the need to believe in higher, extraterrestrial life forms. 
Why would an alien life form automatically qualify as "higher"?
Furthermore there is no such thing as "higher".
Also, we know life is capable of arising in the Universe and given the the billions and billons and billons of planets and stars, (more than each single grain of sand in our oceans), it is not really a leap in logic at all to surmise that life exists elsewhere and may be abundant.
You may do yourself some good to read Carl Sagan and brush up on the Drake equation.