The fact that you think that the alien theory is ridiculous. Out of the all the vast universes and mass amounts of other planets, why does Earth have to be the only planet that can sustain life? Satellites sent into space have brought back picture and recordings of planets that very closely resemble Earth. It showed signs of vegetation and water, two key things needed to sustain life on a planet. There has not been proof yet of the existence of an atmosphere quite yet but once technology advances forward, we shall know for sure. Take a look at this http://www.mnn.com.... This is just one of the many resources that I will be using in my argument about this topic.
while yes there are other shall we call them (duplicate earths) the closet planet to us is mars and scientist and NASA both thought that it could sustain life and it cannot. now these duplicate earths have not shown any signs of life and nor has any other planet. now thats not to say that a planet has to be just like earth to sustain life but we have not had any contact with any other life forms.
I realize this but that does not disprove the theory of other life forms that could possibly be out there. To have all these other planets that could have a possibility not to mention just how many galaxies and stars that could have the potential of our sun to hold this life, is very intriguing. The possibilities are endless for this theory. Who's to say that they have not already been here? We do not know for sure but it could always remain positive. Such structures here like the Easter Island Heads and Stonehenge. Back in these days, we clearly know that we did not have the machines we do today to move these stones that are thousands of pounds in weight. No, I am not saying that this means extraterrestrial life had anything to do with this, but it always remains a possibility until for sure, proven differently.
My opponent brought us the huge arguments such as the easter island heads, and stonehenge. While these are very good things to point out in a debate such as this, i would like to point out that for many years people believed that aliens also built the great pyramids because people thought that humans couldn't lift such heavy objects. this theory however has been disproved.... so while yes stonehenge and the easter island heads are good points i feel as if they are in the same boat as the great pyramids.
I would now like to bring up February 25, 1942. it was on this day that a so called UFO attempted to attack an american air base. the American soldiers unleashed a barrage of AAA (Anti-aircraft artillery) upon the said object but it never was shot down nor was there any debris from this UFO. now over the next couple of days reports of crashed japanese fighter planes that had been shot down were coming in from everywhere. This attack became known as the "Battle of Las Angles" http://mysteriousuniverse.org... this is a link you can go to if you wish to read the story of the "Battle of Las Angles".