A bibliography or a list of references can provide other researchers with a list of sources used for more information. This allows others to locate and verify the sources you have consulted in your research.

within the past six months or so, the Vatican acknowledged the probable existence of extraterrestial occupants of UFO"s but that is as far as it goes.

a UFO See http://grammar.ccc.commnet.edu/grammar/abbreviations.htm (all the way to the bottom) for help determining when to use a or an before an abbreviation.

Ufo's do exist because a Ufo is a thing in the sky that you can not explain.

They usually see UFO's at a UFO sighting