ELI5: Explain Like I'm 5

Rare Earth hypothesis

The Rare Earth hypothesis is a scientific idea that suggests complex life (like animals, plants, and humans) can only exist on planets that have a particular set of rare conditions. This means that planets like Earth, with its perfect mix of temperature, gases, liquid water, and just the right amount of light and dark, are very rare in the universe. Working with this idea, scientists try to explain how and why life is so uncommon in the universe and why we haven't found other forms of life outside of Earth.