A century ago or so, it was popularly thought that Mars was covered with irrigation canals, obviously created by some advanced form of life. That was debunked

A century ago or so, it was popularly thought that Mars was covered with irrigation canals, obviously created by some advanced form of life. That was debunked and the hope shifted to maybe there being some fungus or plants... Such were not found so it shifted to microscopic bacteria. There is perhaps some evidence of those, but nothing conclusive, so now people are talking about cracking open rocks to find the fossils of bacteria... This all has an uncanny resemblance to the "god of the gaps" phenomenon. As science explains more of our world, the religious cram their gods into smaller and smaller gaps in our scientific understanding. And as science shines light on the apparent sterility of Mars, alien life enthusiasts cram their proposed aliens into the ever smaller gaps in our knowledge of Mars.