Water Formation in the Upper Atmosphere of the Early Earth

Abstract

The water concentration and distribution in the early Earthʼs atmosphere are important parameters that contribute to the chemistry and the radiative budget of the atmosphere. If the atmosphere above the troposphere is generally considered as dry, photochemistry is known to be responsible for the production of numerous minor species. Here we used an experimental setup to study the production of water in conditions simulating the chemistry above the troposphere of the early Earth with an atmospheric composition based on three major molecules: N 2 , CO 2 , and H 2. The formation of gaseous products was monitored using infrared spectroscopy. Water was found as the major product, with approximately 10% of the gas products detected. This important water formation is discussed in the context of the early Earth.

Organic chemistry in a CO2 rich early Earth atmosphere

“…because of the saturation of the chromatographic column. This detection of water is in agreement with its previous detection (Fleury et al 2015).…”

“…Indeed, as discussed in Fleury et al 2015, water formed above the troposphere leads to the formation of high altitude clouds analogues to the present PSC and PMC. These clouds are composed of water ice, which would play the role of nucleus cores, promoting a heterogeneous nucleation of organic molecules at the surface of ice grains.…”

“…In (Fleury et al, 2015), the CO 2 consumption efficiency e CO2 is defined according to the following equation (1): Similarly we defined the hydrogen consumption efficiency e H2 with:…”

Molecular hydrogen in oxidized atmospheres of terrestrial exoplanets : Implications for water and oxygen formation

“…The formation of water using a N 2 -CO 2 -H 2 mixture was identified in a previous experimental study focusing on the early Earth with nitrogen as a dominant gas and an initial H 2 mixing ratio fixed at 4% [2]. We now explore various amounts of hydrogen in the mixture to cover the unknown parameters regarding surface emission and to highlight the role played by hydrogen in the chemistry of these exoplanetary atmospheres.…”

CHAPTER 4. Unveiling Early Earth Photochemistry Through Experimental Simulations of Planetary Atmospheres

“…H and H 2 are light molecules that diffused vertically more rapidly than CO 2 and N 2 , so that the upper atmosphere was progressively enriched in H 2 with altitude. Then at high altitude, the coupled photochemistry of CO 2 and H 2 led to a reformation of water at high altitude through the following mechanism 52 :…”