The Faint Young Sun Paradox Revisited

Abstract

We propose a plausible solution to the long-standing paleoclimatology puzzle known as the Faint Young Sun Paradox through a combined two-fold hypothesis that involves the conservation of the radiation balance between the Earth and the Sun, alongside the concept of an Expanding Earth Hypothesis (EHH). As solar luminosity increases, the Earth could maintain stable temperatures by adjusting the height of its atmosphere. This adjustment implies two possibilities depending on whether the solid Earth’s radius is changing: 1) If the radius increases, the Earth would accrete matter from its surroundings (specifically from the solar wind), leading to an increase in the mass of its atmosphere. 2) If the radius decreases, the Earth would naturally expel matter from its atmosphere, resulting in a decrease in its effective mass. We demonstrate that if, as current ITRF observations suggest, the Earth’s landmass is expanding globally at a modest rate of approximately 0.45 ± 0.05 mm∙yr − 1 , and if the Earth’s atmosphere has a vertical height of about one-third of the Earth’s radius (approximately 2860 km from the surface), it becomes plausible to explain the presence of liquid water on the Earth’s surface around 3.20 ± 0.70 Gyr ago during the Archaean eon , when the Sun was about 75% as luminous as it is today. Additionally, this framework can account for the current radial expansion rate of the Earth. Ultimately, we view the Earth system as an auto-self-regulating incubator , where this self-regulating mechanism arises from the Earth’s atmosphere automatically adjusting its height in response to changes.