Origin and evolution of the atmospheres of early Venus, Earth and Mars
The origin and evolution of early Venus, Earth and Mars is discussed. Formation scenarios of terrestrial planets are reviewed since their protoplanets have been released from the protoplanetary disk a few million years after the Sun and the planets came into being. When protoplanets accrete a certain mass, while they are embedded in the gas disk, thin H2 envelopes are captured from the nebula. In late stage planet formation planets do not accumulate nebula gas because they accrete to larger masses after the disk disappeared. The differences between these two scenarios are discussed by investigating non-radiogenic noble gas (i.e., 20Ne, 36Ar, 84Kr, 130Xe) isotope anomalies observed in the 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. Contrary to proto-Venus and proto-Earth, on early Mars due to its low mass, no efficient nebula-based H2-envelope could be accumulated. Depending on the young Sun’s EUV flux history, Mars’ magma ocean related outgassed steam atmosphere could have been lost during the first hundred Myrs. A volcanically outgassed secondary atmosphere CO2-dominated atmosphere with a surface pressure of a few hundred mbar was most likely lost by a complex interplay of various nonthermal atmospheric escape processes, impacts, carbonate precipitation, and serpentinization during the past 3.5 - 4.0 Gyr ago. On early Earth, the complex interplay between the atmosphere-surface-interaction related CO2 carbonate-silicate cycle, surface weathering and the outgassing of nitrogen is discussed. The relevant factors related to the solar EUV flux evolution scenario during Earth’s Archean epoch, where an outgassed N2 atmosphere was most likely slightly enriched in 15N isotopes by atmospheric escape compared to the primordial mantle nitrogen, is addressed. A discussion on how Earth`s earliest life forms modified the atmosphere since the Archean. Finally, the evolution of Earth’s atmosphere in relation to the discovery of possible habitable terrestrial exoplanets finalizes the talk.