Presence of a primary solar-type atmosphere around the earth: evidence of dissolved noble gas

Abstract

Recent noble gas data of mantle-derived samples show that there are two end members: PLUME-type and MORB-type. The estimated high 3He and 22Ne abundances of the PLUME source, possibly representing the lower mantle, should reflect the remnant of dissolved solar-type atmosphere. Calculations of the structure of the primary atmosphere and the noble gas dissolution into the magma ocean of the accreting planet suggest that the high 3He and 22Ne abundances can be explained if the primary atmosphere persisted until M∼0.4–0.6 M E ( M E being the present Earth mass). The PLUME source has higher 3He/ 4He and lower 21Ne/ 22Ne than the MORB source. This is explained by assuming that the lower mantle was less degassed during magma ocean cooling. The carbon abundance in the mantle can be constrained from the estimated abundance of mantle 3He and C/ 3He data of the present mantle-derived samples. Dissolved solar-type noble gas might explain high noble gas abundance in the present Venus, if the primary atmosphere persisted until the final stage of accretion under lower dust opacity of the atmosphere.