Cretaceous
Overview
The Cretaceous was a geologic period and system that spanned 79 million years from the end of the Jurassic Period 145 million years ago (mya) to the beginning of the Paleogene Period 66 mya. It was the last period of the Mesozoic Era, and the longest period of the Phanerozoic Eon. The Cretaceous was characterized by a warm climate, high sea levels, and the proliferation of new types of plants and animals.
Climate
The Cretaceous was generally warm, with little or no evidence of glaciation. The poles were temperate, which allowed for a diversity of ecosystems. The climate was also very humid, with evidence of extensive tropical rainforests. The high sea levels during the period resulted in numerous shallow inland seas. These conditions are believed to have been caused by high levels of CO2 in the atmosphere.
Flora
The Cretaceous was a time of great change in the flora of the Earth. The early Cretaceous saw the spread of gymnosperms, which were gradually replaced by angiosperms (flowering plants) in the late Cretaceous. This shift in plant life had a profound impact on the herbivorous dinosaurs, which had to adapt to the new types of vegetation.
Fauna
The Cretaceous was a time of great diversification in animal life. The period saw the evolution of many new types of dinosaurs, including the first appearance of T. rex, Triceratops, and Velociraptor. It was also during this time that the first birds, such as Archaeopteryx, evolved. The Cretaceous seas were populated by large marine reptiles, such as Ichthyosaurus and Plesiosaurus, as well as the first true mammals.
Extinction Event
The end of the Cretaceous is marked by one of the most significant extinction events in Earth's history, known as the K-Pg extinction event. This event, which occurred approximately 66 million years ago, resulted in the extinction of approximately 75% of all species on Earth, including all non-avian dinosaurs. The cause of this extinction event is widely believed to be the impact of a large asteroid or comet near what is now the Yucatan Peninsula in Mexico.
