Rare Earth

DrNoGods wrote:This, combined with the fact that we do have one planet that supports life, suggests a high likelihood that life exists elsewhere in the universe. Statistically, the probability is very high.

Just because we are on a planet with life does not necessarily lead to a high probability life exists elsewhere. As we understand more about our planet and it’s uniqueness, the odds of an exoplanet being able just to support life progresses lower.

The Rare Earth hypothesis argues that the evolution of biological complexity requires a host of fortuitous circumstances, such as a galactic habitable zone, a central star and planetary system having the requisite character, the circumstellar habitable zone, a right-sized terrestrial planet, the advantage of a gas giant guardian like Jupiter and a large natural satellite, conditions needed to ensure the planet has a magnetosphere and plate tectonics, the chemistry of the lithosphere, atmosphere, and oceans, the role of “evolutionary pumps” such as massive glaciation and rare bolide impacts …


And the above conditions are just to have the environment that is necessary for life to begin. Once you factor in life actually trying to evolve, the odds become much smaller of any other life existing.