The origin and evolution of the atmospheres of Earth, Venus and Mars are reviewed from the time when their protoplanets were released from the protoplanetary disk a few million years after the Sun came into being. The early disk-embedded phase of the evolution of protoplanetary cores that can accumulate gas from the disk and form thin planetary H 2-envelopes is also discussed. This scenario is compared to cases of late stage planet formation, where terrestrial planets accrete from large planetary embryos after the protoplanetary disk already disappeared. The differences between these two scenarios are discussed by investigating non-radiogenic noble gas isotope anomalies observed in the present atmospheres of the three planets. The role of the efficiency of the young Sun's EUV radiation and solar wind to the escape of early atmospheres is also discussed. The catastrophic outgassing of volatiles and the formation and cooling of steam atmospheres after the solidification of magma oceans is addressed together with the geochemical evidence of additional delivery of volatile-rich chondritic materials during the main stages of planetary formation. Unlike early Venus and Earth, no nebula-based H 2-envelope could be accumulated on early Mars due to its low planetary mass. According to the young Sun's luminosity and EUV flux history, Mars' magma ocean related outgassed steam atmosphere could have been lost during the first hundred Myrs. Depending on the young Sun's EUV flux, the presence of greenhouse gases, impacts, and the amount of greenhouse gases outgassed additional to that from the magma ocean, Mars could have developed episodically standing bodies of liquid water

The magma ocean (MO) is a crucial stage in the build-up of terrestrial planets. Its solidification and the accompanying outgassing of volatiles set the conditions for important processes occurring later or even simultaneously, such as solid-state mantle convection and atmospheric escape. To constrain the duration of a global-scale Earth MO we have built and applied a 1D interior model coupled alternatively with a grey H 2 O/CO 2 atmosphere or with a pure H 2 O atmosphere treated with a line-by-line model described in a companion paper by Katyal et al. (2019). We study in detail the effects of several factors affecting the MO lifetime, such as the initial abundance of H 2 O and CO 2 , the convection regime, the viscosity, the mantle melting temperature, and the longwave radiation absorption from the atmosphere. In this specifically multi-variable system we assess the impact of each factor with respect to a reference setting commonly assumed in the literature. We find that the MO stage can last from a few thousand to several million years. By coupling the interior model with the line-by-line atmosphere model, we identify the conditions that determine whether the planet experiences a transient magma ocean or it ceases to cool and maintains a continuous magma ocean. We find a dependence of this distinction simultaneously on the mass of the outgassed H 2 O atmosphere and on the MO surface melting temperature. We discuss their combined impact on the MO's lifetime in addition to the known dependence on albedo, orbital distance and stellar luminosity and we note observational degeneracies that arise thereby for target exoplanets.

Context. Plate tectonics is considered a fundamental component for the habitability of the Earth. Yet whether it is a recurrent feature of terrestrial bodies orbiting other stars or unique to the Earth is unknown. The stagnant lid may rather be the most common tectonic expression on such bodies. Aims. To understand whether a stagnant-lid planet can be habitable, i.e. host liquid water at its surface, we model the thermal evolution of the mantle, volcanic outgassing of H 2 O and CO 2 , and resulting climate of an Earth-like planet lacking plate tectonics. Methods. We used a 1D model of parameterized convection to simulate the evolution of melt generation and the build-up of an atmosphere of H 2 O and CO 2 over 4.5 Gyr. We then employed a 1D radiative-convective atmosphere model to calculate the global mean atmospheric temperature and the boundaries of the habitable zone (HZ).Results. The evolution of the interior is characterized by the initial production of a large amount of partial melt accompanied by a rapid outgassing of H 2 O and CO 2 . The maximal partial pressure of H 2 O is limited to a few tens of bars by the high solubility of water in basaltic melts. The low solubility of CO 2 instead causes most of the carbon to be outgassed, with partial pressures that vary from 1 bar or less if reducing conditions are assumed for the mantle to 100-200 bar for oxidizing conditions. At 1 au, the obtained temperatures generally allow for liquid water on the surface nearly over the entire evolution. While the outer edge of the HZ is mostly influenced by the amount of outgassed CO 2 , the inner edge presents a more complex behaviour that is dependent on the partial pressures of both gases. Conclusions. At 1 au, the stagnant-lid planet considered would be regarded as habitable. The width of the HZ at the end of the evolution, albeit influenced by the amount of outgassed CO 2 , can vary in a non-monotonic way depending on the extent of the outgassed H 2 O reservoir. Our results suggest that stagnant-lid planets can be habitable over geological timescales and that joint modelling of interior evolution, volcanic outgassing, and accompanying climate is necessary to robustly characterize planetary habitability.