Personally i don't think religion works well with science as it inherently sets people up against each other. The one thing really every religion has in common is that at their core, they all think the other religions must be wrong or why follow theirs? Not to go off topic but they may be somewhat related in making this point in regards to human beings collective ego.
I agree with this statement. While treading as lightly on religion as possible, in my perspective, I see two kids playing in a sand box with some toys. One kid wants to play with Hotwheels and the other wants to play with Tonka trucks. While each have their obvious differences, they also share their similarities but the two kids can't seem to agree on what to play with. This senario also applies to science and religion. Church =/= Lab; Priest =/= Professor; Bishop =/= Scientist; Bible =/= Thesis and so on. Which ever side of the sandbox you land on, you will find that you will tend to disagree with the other side on how you spend your time playing in the sand box. But what both sides, more often than not, fail to agree on is: What is outside of the sandbox? We can look and debate but neither side can say exactly what is out there.
I think one would be naive and narcisistic to think that there isn't at least something out there in the vast expance of space that would be intelligent enough to design a craft for interstelar travel. I have seen people who bring up the distance to the next possible planet to inhabit intelligent life and the time it would take to travel such a distance. They tell me that this would be near impossible to accomplish. I feel this again is a humanized narcisistic point of view being that humans only live for only so long. Traveling at near lightspeeds, one's life would surely expire before reaching the next inhabitable planet but what life spans would the aliens have. 100 years? 200 years? 1000 years? A longer life span would be an important factor in deciding if a trip to another inhabitable planet such as Earth would be possible.
If life started billions of years ago in our solar system and hypithetically, intellegence made its appearance 1 billion years ago, what if in the alien's solar system intellegence started 20,000 years (an extremely short time in the life of the universe) before it started in our system, would it be possible that the aliens would be able to use a technology 20,000 years more advanced than ours? Would it be possible that we may be able to weild the same technology in the next 20,000 years as well? I think so but, no one can say that for sure. 20,000 year head start, longer life span, all lead to the speculation of the possibility that they may have been here at one point in time. What they were here for? You'd have to ask them. They may have used our plant as a rest stop while puddle jumping to some other planet or somesort of documentry for their History channel on Omicron Percei 8. The rest stop idea would explain why they are no longer here but again, entirely speculation.
As far as the "Where's the launch pad?" question asked a few posts ago. You will be able to find chuncks of randomly formed glass in the desert in north Africa. As we all know, glass is sand heated to extreme tempratures and our planet is a dynamic one. It will change, errode, and move through time. Plants will grow, wind will blow and water will wash away trace evidence to support this hypothosis (not a theroy as it has not been tested to my knowledge).
I am not saying that there is yes or no answer to these questoins but only a definite maybe. I have not seen this show but, after reading this thread, I want to watch it now. But, what I find funny is that this type of program would find itself on the "History" Channel.