Evolution of Atmospheric Oxygen Escape from Earth During the Last 2.45 Billion Years

Understanding atmospheric escape over geological timescales is essential for constraining a planet's capacity to retain its atmosphere and sustain life. Earth’s atmosphere has drastically changed in composition, with a significant increase in oxygen occurring during the Great Oxidation Event (GOE) 2.45 Gyr ago. Atmospheric oxygen can be ionized and energized by solar radiation and plasma interactions involving the solar wind, the magnetosphere, and ionosphere, eventually leading to its escape into space either as a neutral or as an O+ ion.

 

For Earth, the main challenge of this work lies in estimating past escape rates from the extrapolation of present-day observations to the younger solar system environment, since the GOE, when an increase of atmospheric oxygen is observed in the geological record.

To achieve this, we developed a semi-empirical model, that considers seven different escape mechanisms to estimate the time evolution of the average oxygen escape rate. We consider the evolution of the solar wind and solar radiation, the Earth’s magnetic moment, and the Earth’s exosphere while assuming a constant atmospheric composition. The escape rate of each escape mechanism is calculated considering analytical formulas, a physical scaling and/or empirical formulas.

 

During the last 2.45 Gyr., oxygen escape from Earth was dominated by the escape of oxygen ions through the polar wind and polar cusp escape. We estimate that the past oxygen escape rate was more than one order of magnitude higher than now, reaching a total escape rate above 10²⁷ s^-1 at the time of the GOE, and that the total oxygen loss during the last 2.45 Gyr corresponds to 63% of the current atmospheric oxygen content. We discuss the role of key parameters that determine atmospheric escape for a magnetized planet, as Earth.