There is no purpose to life. Life exists because of probability. There are infinite number of universes . Some have no life forms, some have different kind of life forms. Our universe is one which supported intelligent life forms such as you and me. And because we existed in this universe we ask this type of questions. There are multitude of other universes where no one is around to ask the question. You think this universe is special because human are able to think and ask why we exists. So I repeat, there is no purpose to life. This just my own pet theory feel free to argue it.

If you read TS opening topic carefully, he is asking the purpose of life. Whether aliens exists or not is irrelevant to the topic.