Illustration of pterosaurs over a Cretaceous landscape, in a time when Earth was warmer than today MasPix / Alamy During the past 500 million years – the time when animals and land plants evolved – the average surface temperature of the planet varied more widely and got even hotter than previously thought. The mean global surface temperature over this time was 24°C (75°F) and sometimes reached 36°C (97°F), compared with around 14°C or 15°C (57-59°F) at present. The lowest it got was around 11°C (52°F) according to the most rigorous study so far.
“Our research suggests that temperatures during greenhouse intervals [when CO2 levels are high] can get warmer than is indicated by previous [studies],” says Emily Judd of the Smithsonian National Museum of Natural History in Washington DC. In fact, during the hottest periods, average surface temperatures in the tropics reached 42°C (108°F), according to the study, meaning some land areas could have been too hot for plants and animals to survive . Even polar regions were warm during these times , with average temperatures exceeding 20°C (68°F).
“There were likely a few times over the last half billion years where certain regions were uninhabitable, or where the biodiversity in those regions was extremely low,” Judd says. Her team also found a stronger link between carbon dioxide levels in the atmosphere and average global temperature than expected. Over such a long time span, the team had expected the relation.