Hydrogen-Nitrogen Greenhouse Warming in Earth's Early Atmosphere

Abstract

Faint Young Sun During the first ∼billion years after the formation of Earth, the Sun was significantly less luminous than today, delivering considerably less solar energy to our planet. Nevertheless, the geological record shows that Earth harbored liquid water and was not frozen—as would be expected on the basis of the reduced solar output. The presence of liquid water on Earth during this time is referred to as the “faint young Sun” paradox. Wordsworth and Pierrehumbert (p. 64 ; see the Perspective by Kasting ) suggest a new explanation for this mystery, invoking absorption of solar radiation owing to collisions between atmospheric H 2 and N 2 as a source of heating. This mechanism could have supplied enough extra warming to keep surface temperatures above 0°C.