48 million years ago, Messel was dominated by a tropical climate. The lake was surrounded by a dense jungle that was home to a wide variety of animals and plants. The air was warm and humid and the ground was swampy. At that time, dinosaurs had already been extinct for 18 million years. During the Eocene, the mean annual temperature was about 10 degrees higher than today. The ice of the polar caps had melted, and large parts of Europe were covered by a shallow sea. Tropical-type forests like the one in Messel were found across all of Germany.