The evolution of Venus’ early water inventory

One can separate the atmospheric evolution of Venus into two epochs. The first epoch lasts from the final accreted planet 4.5 Gyr ago to the "last" resurfacing that occurred about 200-1000 Myr ago. The second epoch lasts from this resurfacing event until today. The evolution of Venus’ atmosphere during the beginning of the first epoch was exposed by very high solar EUV flux values, probably, water that was produced from the interaction between a primordial atmosphere and a magma ocean, water that was incorporated into the planet’s accretion from carbonaceous chondrites or a mixture of both sources. The different water sources have different initial D to H ratios, which could have been fractionated due to atmospheric escape. Here we will investigate how thermal escape processes may have affected or modified water-based initial D/H ratios after the planet’s origin to the last resurfacing a few hundred Myr ago.  By knowing the loss rates of H₂O from the planet’s origin to the time when the "last" resurfacing occurred, including the corresponding D/H ratio, allows us to make statements about the planet's water balance, since the ratio evolution during the above-mentioned second epoch is dominated by photochemical non-thermal H and D loss processes.