The Paleozoic

The Paleozoic is the earliest era of the Phanerozoic. It started around 550 million years ago and lasted approximately 300 million years. The name Paleozoic means "ancient life", since it was during this era that Earth's environment became conducive to the spread of new, complex life forms. The era consists of six periods; the Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian. During the Cambrian period, a vast majority of Earth's crust was submerged under water and new nutrients were being added to the atmosphere. These were the conditions in which new species evolved. Organisms, the best known being the trilobites, filled the seas. The transition to the Ordovician period was marked by lower sea levels and the evolution of new predators and prey that were more specialized and complex. At the end of this period the first land plants evolved. During the Silurian and the Devonian the expansion of marine life continued. Early land animals and the first true forests, consisting of mosses and ferns, were also manifested during these two periods. Primitive insects and arachnids have been dated back to the Silurian; and in the late Devonian, amphibians evolved as species of fish made their way out of the water and on to land. During the late Paleozoic, the slow, constant movement of continents against one another created the supercontinent Pangea. During the Carboniferous the first land vertebrates evolved. Some of these animals were the predecessors to the dinosaurs that roamed Earth in the Mesozoic. In the Permian the forests spread and seed-bearing trees and other plants evolved. The end of the Permian, which is the last period of the Paleozoic, was marked by a mass extinction brought about by a combination of events. The extinction was not sudden, it is hypothesized to have lasted approximately 8 million years. By the end of it, over 95 percent of Permian marine species had become extinct.