The Paleozoic and Mesozoic ERAS are two of the three major divisions of geologic time. The Paleozoic Era began about 541 million years ago and ended about 252 million years ago. It is characterized by the emergence of life in the oceans and the colonization of land by plants and animals. The Mesozoic Era followed the Paleozoic and lasted from about 252 million years ago to 66 million years ago. This era is known as the 'Age of Reptiles' and saw the rise of the dinosaurs.