Geology: Laurasia and Gondwanaland were finally separated in the early Cretaceous. Later, South America separated from Africa and Australia from Antarctica. Evolution took a twist there. In the Cenozoic, "toothless" mammals and marsupials evolved in those separate places. India also detached from Gondwanaland about 100 million years ago, establishing its 8000-km long journey to the rest of Asia. The Cretaceous climate was very warm and wet. Rainfall levels were similar to that of today. Animal Life: Dinosaur species were at their peak in the Cretaceous. In the seas, large ammonites (rather like a rolled-up squid in a shell) and reptiles such as Plesiosaurs and Ichthyosaurs thrived. The skies were abundant with pterosaurs and newly evolved birds. All seemed well in the world, but 65 million years ago, most creatures in the land, sea, and sky became extinct. Even the gigantic dinosaurs all died out. Although no one knows yet why this happened, the general scientific populace supports the theory that there was a climate change on earth that the creatures could not adapt to. It is a mystery, though, how this occurred. The most supported theory is that of a large comet hitting the earth and spewing dust and debris into the air. An event like this would have blocked sunlight, causing a cooling in the earth's climate. In turn, cold-blooded animals would die out. In recent years, scientists have found a possible crash site off the Yucatan Peninsula in Mexico. Another climatic change theory is one where volcanoes spit out a lot of dust, also blocking the sun's rays. Other explanations exist: A tremendous increase in solar radiation. A reversal of the earth's magnetic field. Plants turned alkaline, and dinosaurs could not survive on them. A "Black Death" swept the land. Egg-eating mammals swiped the dinosaur's eggs. These theories though, have not been proven, and some do not account for reductions in the waters and skies. And why didn't mammals, crocodiles, and birds die out? This extinction remains in large part a mystery. Plant Life: The Mesozoic pants like ferns, horsetails, ginkgoes, and cycads, all flourished in this period. But there was also an increase in flowering plants called angiosperms (read about those in the Cenozoic). That includes grass, and fruits and vegetables. It would become a major evolutionary effect in the coming years. In the extinction, most of the warm, moist-loving plants were replaced by the flowering ones.	Dinosaurs flourished in the Cretaceous.
	The major theory of extinction is a comet.

Mesozoic Era: Cretaceous Period