 Faint young Sun paradox

The Faint Young Sun Paradox refers to an apparent contradiction in our understanding of the early Earth's climate and the evolution of life. According to astrophysical models of the Sun's evolution, the Sun was significantly less luminous during its early years—about 30% dimmer—as it was a younger star in the process of fusing hydrogen into helium. If the Sun was indeed fainter, it raises questions about how early Earth maintained liquid water on its surface and supported life.