The Earth's surface was much cooler at 3.42 billion years ago than previously thought---perhaps even temperate. Working with collaborators at Yale and Stanford, we examined the hydrogen and oxygen isotopic compositions of rocks from the Buck Reef Chert in South Africa (picured above). These compositions are determined by the composition and temperature of the water from which the rocks originally precipitated. By analyzing both isotopic systems, we were able to estimate possible ranges of both early ocean composition and temperature and suggest that the Buck Reef Chert ocean was no hotter than 40 degrees Celcius. Previous studies examining oxygen alone had suggested temperatures between 55 and 85 degrees Celcius. The range implied by those hotter temperatures straddles the thermal upper limit for modern photosynthetic organisms, but our new estimate suggests a world more amenable to photosynthetic bacteria.

This study is reported in the journal Nature. For more information, see the Texas A&M press release.