The idea of ice sheets during the age of dinosaurs has always been a controversial topic. Nevertheless, McElwain and coauthors Steve Hesselbo, from the Department of Earth Sciences at the University of Oxford in England, and Jessica Wade Murphy, who was an undergraduate student in the Department of Ecology and Evolution at the University of Chicago at the time of this study, believe they have tantalizing evidence that the global temperatures were not as uniformly warm and ice free during the age of dinosaurs, as once assumed. In this study, which was funded by the Comer Foundation of Science and Education, atmospheric carbon dioxide levels were determined by counting the stomata in small fossil leaves collected from Bga Formation, Denmark, of which 126 specimens were used. Stomata are minute pores in the surface of leaves through which water vapor and gases, including carbon dioxide, pass. The fewer the stomata, the more carbon dioxide in the atmosphere, and vice versa.
"We were certainly surprised to find that our tiny fossil leaves from Denmark led us half way across the world to coalfields of the Transantarctic Mountains in Antarctica to form a new theory on how natural geological processes in the past have caused extreme global warming," McElwain said. "It's very sobering to realize that humans are currently causing global warming by similar processes, that is, by burning fossil fuels like coal and oil. The difference today is that we are causing the atmosphere and climate to change at a greatly faster rate than has ever been observed in the Earth's history."