Maybe the reason we haven’t found Extraterrestrial Alien Civilizations is because they were already here. This is the Silurian Hypothesis. Named after a Dr. Who episode. Did an intelligent race of reptilian humanoids rule the earth 350 million years ago? After 50 million years how could you tell? What trace evidence would remain and where? What can we use from human history and geology to provide clues where to look? This will be an open discussion, but we will stick to the main premise and what we can reasonably extrapolate from our knowledge of science as we examine the evidence of what is currently known. So that means inter-dimensional aliens who live in the sun are off the table. That’s for another panel.