Sea surface temperatures during the early Cretaceous period, about 142-128 million years ago, were warmer than previously thought, and at least five degrees Celsius warmer than today, according to a paper published online this week in Nature Geoscience.

Kate Littler and colleagues used organic compounds preserved in marine sediments to reconstruct sea surface temperatures from sites in the North Atlantic and Indian oceans. They found that temperatures were generally warm and stable throughout the 14-million-year period. Moreover, the temperature difference between the mid- and low-latitudes was minimal, relative to that found today. This was mostly the result of unusual warmth recorded at the mid-latitude Indian Ocean site, with temperatures about 16 degrees Celsius warmer than at present.