The universe is billions of years old and the likelihood that two advanced civilizations meet is extremely rare in fact there's a greater likelihood that these civilizations implode on themselves (i.e. Nuclear War). If an alien species visited earth they would be here for our resources. Take a look outdoors during the summer and imagine every flicker of firefly represents 100k years of civilization floating around in the universe.
Originally Posted By: OneEyeJack
You'd think there would be something, some kind of evidence somewhere from the past few thousand years of life as we know it.