The Mesozoic and Paleozoic Eras are two of the three major divisions of geologic time. The Mesozoic ERA, also known as the Age of Reptiles, lasted from about 252 million to 66 million years ago. It is divided into three periods: Triassic, Jurassic, and Cretaceous. The Paleozoic ERA, which lasted from about 541 million to 252 million years ago, is divided into six periods: Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian. Both eras were characterized by the emergence of life forms on land and in the oceans.