Science. 1971 Mar 12;171(3975):1015-6. doi: 10.1126/science.171.3975.1015.
Sedimentary barites from the Swaziland System of South Africa (more than 3000 million years old) have sulfur-34 ratios that are enriched by only 2.5 per mil with respect to contemporary sulfides. To explain this small fractionation, it is proposed that oxygen pressure in the earth's atmosphere was very low and that local oxidation occurred in a photosynthetic layer of the ocean.
南非 Swaziland 系的沉积重晶石（已有 3 亿多年历史）的硫-34 比值相对于现代硫化物仅富集了 2.5‰。为了解释这种小分馏作用，有人提出当时地球大气中的氧分压非常低，并且局部氧化作用发生在海洋的光合层。
