Part 2/10:

Around four billion years ago, Earth teetered on the edge of life's emergence, yet paradoxically, the conditions suggested it should have been inhospitable. The Sun's luminosity was approximately 30% weaker, suggesting our young planet was a lifeless icy desert, far beyond the habitable zone. Highly advanced hypothetical alien civilizations, observing Earth with powerful telescopes, would have dismissed it as unsuitable for life.

However, that's where the mystery begins—scientists are confident that life did indeed arise at this seemingly unsuitable time, indicating an anomaly known as the "Faint Young Sun Paradox." Pioneering astronomer Carl Sagan, along with his colleague George Mullen, identified this inconsistency in the 1970s, igniting a quest for understanding.