The early evolution of Venus and Earth
The atmospheric noble gas isotope and elemental bulk ratios on Venus and Earth provide important information on their origin and evolution. While they were still accumulating mass, these planets captured significant hydrogen dominated atmospheres by capturing gas from the disk, which was then lost by hydrodynamic escape after the disk dissipated. After a short but efficient boil-off phase the EUV-driven hydrodynamic flow of H atoms dragged heavier elements with it at different rates, leading to changes in their ratios. The results that allow the reproduction of present day elemental observations, reveal the early activity/rotation history of the young Sun, the protoplanetary masses of early Venus and Earth at the time when the disk dissipated. Finally the results indicate a fast accretion of thermally-processed disk material into asteroidal bodies and/or planetary embryos, and are in agreement with 182Hf-182W chronometric fast accretion scenarios of the proto-Earth, and a noble gas origin based on a mixture of primitive meteoroids and a small remnant of the proto-solar nebula.