faint young Sun paradox

The "faint young Sun paradox" addresses the apparent contradiction between the Sun's lower luminosity in its early history and the evidence of liquid water on early Earth. Astrophysical studies suggest the Sun was significantly dimmer, which should have resulted in a frozen planet. However, geological evidence indicates liquid water existed, implying a warmer early Earth.12

The solution likely lies in higher concentrations of greenhouse gases, such as methane and carbon dioxide, in Earth's early atmosphere. These gases would have trapped more heat, counteracting the Sun's weaker output. As the Sun's luminosity increased over time, these greenhouse gas concentrations must have decreased proportionally, suggesting a feedback mechanism regulated them. Rock weathering and biological processes are considered potential regulators that removed carbon dioxide from the atmosphere.13