# Evolution and Spectral Response of a Steam Atmosphere for Early Earth with a coupled climate-interior model

## TL;DR

This study models Earth's early steam atmosphere during the magma ocean phase, analyzing its spectral response and the effects of thermal dissociation, to better understand early planetary conditions and potential observational signatures.

## Contribution

It introduces a coupled climate-interior model with detailed radiative transfer and chemical equilibrium calculations for early Earth's steam atmosphere, including spectral features of dissociation products.

## Key findings

- Magma ocean duration extends by several million years with a pure water atmosphere.
- Thermal dissociation reduces outgoing longwave radiation by 1-6%.
- Spectral features of H₂, O₂, and H₂O vary with altitude and can inform exoplanet observations.

## Abstract

The evolution of Earth's early atmosphere and the emergence of habitable conditions on our planet are intricately coupled with the development and duration of the magma ocean phase during the early Hadean period (4 to 4.5 Ga). In this paper, we deal with the evolution of the steam atmosphere during the magma ocean period. We obtain the outgoing longwave radiation using a line-by-line radiative transfer code GARLIC. Our study suggests that an atmosphere consisting of pure H$_{2}$O, built as a result of outgassing extends the magma ocean lifetime to several million years. The thermal emission as a function of solidification timescale of magma ocean is shown. We study the effect of thermal dissociation of H$_{2}$O at higher temperatures by applying atmospheric chemical equilibrium which results in the formation of H$_{2}$ and O$_{2}$ during the early phase of the magma ocean. A 1-6\% reduction in the OLR is seen. We also obtain the effective height of the atmosphere by calculating the transmission spectra for the whole duration of the magma ocean. An atmosphere of depth ~100 km is seen for pure water atmospheres. The effect of thermal dissociation on the effective height of the atmosphere is also shown. Due to the difference in the absorption behavior at different altitudes, the spectral features of H$_{2}$ and O$_{2}$ are seen at different altitudes of the atmosphere. Therefore, these species along with H$_{2}$O have a significant contribution to the transmission spectra and could be useful for placing observational constraints upon magma ocean exoplanets.