The Faint Young Sun Paradox and Why Trees Are Green

The article is devoted to the significantly underestimated contribution of radiation from the young Sun to the formation of physical conditions on the early Earth. A new view on the faint young Sun paradox is presented: the main role in solving the paradox is given to the impact of the increased activity of the young Sun on the Earth’s atmosphere. The role of planetary organic films is considered as a climate-forming factor involved in resolving the faint young Sun paradox. The spectrum of radiation of the young Sun and the paradox of the discrepancy between the chlorophyll absorption spectrum and the spectrum of solar radiation are discussed, and also indicated a possible connection between the faint young Sun paradox and the origin and evolution of photosynthesis on Earth.