Oxygen and hydrogen isotope evidence for a temperate climate 3.42 billion years ago

The study of stable oxygen isotope ratios (δ18O) of Precambrian cherts suggests that ocean temperatures during the Archaean era (about 3.5 billion years ago) were between 55 °C and 85 °C, but uncertainty about the δ18O of the primitive ocean has led to considerable debate regarding this conclusion. Here, a combined analysis of oxygen and hydrogen istopes sampled from 3.42-billion-year-old Buck Reef Chert rocks in South Africa indicates that the ancient ocean was much cooler than previously thought.