Dinosaurs had to cope with dramatic swings in the climate around 120 million years ago, with ocean surface temperatures changing by as much as 6 °C. The finding suggests that natural climate variations are much more complex than previously thought.Simon Brassell from Indiana University, Bloomington, and colleagues examined telltale carbon compounds in fossilised bacteria. The proportion of these compounds varies with water temperature, and bacteria from different rock layers revealed that the ocean surface temperature went from around 30 °C to 36 °C in the space of 10,000 years (Geology, vol 34, p 833). "The changes appear step-like, as if the climate is switching from one mode to another," Brassell says.