Analyses of ancient sulfide minerals and the modern organisms that create sulfides are giving scientists a better idea of what Earth's atmosphere and oceans may have been like billions of years ago. The findings may also explain a paradox that has long puzzled solar astronomers.
In one of the new studies, scientists looked at the ratio of isotopes in sulfide particles trapped in diamonds unearthed from a mine in Botswana. Radioactive dating shows that those gems formed about 2.9 billion years ago, says Mark H. Thiemens, a chemist at the University of California, San Diego.
In the Dec. 20, 2002 Science, Thiemens and his colleagues argue that their data–in particular, a higher-than-normal proportion of sulfur-33 in the inclusions–can only be explained by certain atmospheric chemical reactions that are stimulated by specific wavelengths of ultraviolet light. Today, those wavelengths are screened from most of Earth's atmosphere by ozone (O3) and oxygen