Old passage:
"Space contains such a huge supply of atoms that all eternity would not be enough time to count them and count the forces which drive the atoms into various places just as they have been driven together in this world. So we must realize that there are other worlds in other parts of the universe with races of different men and different animals"
Answer (Paraphrased Passage):
Mathematically speaking, it is impossible to count the forces which distribute and regulate the activities of the atoms that make up our planet how much more the vastness of space.
Because of this we have come to a realistic assumption that on the balance of probability life must exist in other parts of the universe besides ours the form of a different kind of men and animals.
Cheers!