Mars, the "Great Filter," and Extraterrestrial Life
The discovery of extinct life on Mars would furnish evidence for what some pessimistic cosmologists call the "Great Filter"--a theorized congeries of conditions obtaining throughout the universe, under which the chances of life anywhere developing civilizations capable of interstellar travel are impossibly small.
This doesn't mean that life never arises elsewhere; it only means that the chance of it arriving at the stage at which it can voyage among the stars is effectively zero.
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