Primordial helium and neon in the Earth - A speculation on early degassing

Abstract

Primordial helium-neon abundance ratios in the Earth have been accurately determined, based on helium and neon isotopic systematics observed in mid-ocean ridge basalts (MORBs) and Hawaiian ocean island basalt (OIB) samples. The mean primordial 3He/22Ne ratios for the MORB and Hawaiian OIB samples are 10.2 ± 1.6 and 6.0 ± 1.4, respectively. The gross average of all values is 7.7 ± 2.6, about twice the solar 3He/22Ne ratio of 3.8. Thus, primordial helium and neon in the Earth are elementally fractionated from the solar composition, noting, however, that the Earth's primordial helium and neon are isotopically solar in composition. This elemental fractionation between helium and neon was probably caused by solubility-controlled degassing processes at an early stage of the Earth's evolution.