Fig. 4: Relationship between TiO₂ contents and ⁴He/³⁶Ar and ²⁰Ne/³⁶Ar ratios of the lunar soils.

The number in the brackets indicates the soil grain size(the unit of the grain size is μm). The data of the Apollo and the Luna soils are from ref. ^{17,50,51,52,53,54,55,56}.