Fractal organic hazes provided an ultraviolet shield for early Earth.

The Archean Earth (3.8 to 2.5 billion years ago) was probably enshrouded by a photochemical haze composed of fractal aggregate hydrocarbon aerosols. The fractal structure of the aerosols would have had a strong effect on the radiative properties of the haze. In this study, a fractal aggregate haze was found to be optically thick in the ultraviolet wavelengths while remaining relatively transparent in the mid-visible wavelengths. At an annual production rate of 10(14) grams per year and an average monomer radius of 50 nanometers, the haze would have provided a strong shield against ultraviolet light while causing only minimal antigreenhouse cooling.