The Faint Sun Paradox

For decades, astrophysicists and geologists have been locked in a debate over a fundamental contradiction in Earth's history known as the Faint Young Sun Paradox. Standard solar models indicate that four billion years ago, the sun was approximately 30% dimmer than it is today. Under such conditions, Earth should have been a frozen wasteland, yet geological evidence—such as ancient sedimentary rocks—proves that liquid water existed and life actually thrived. This mystery forces us to ask: how did a younger, weaker sun keep our planet warm enough for life to begin?The Faint Young Sun Paradox remains a cornerstone of astrobiology because it defines the "habitable zone" of our solar system. Understanding how Earth maintained its liquid oceans under a faint sun not only explains our own origins but also helps us identify which distant exoplanets might be capable of supporting life.