What are the major eras of prehistoric life on earth?
The Precambrian Era was the time before life from the birth of the planet until first simple marine organisms appear in the fossil record. Because the algae and simple single and multiple-celled organisms of this time were all soft and microscopic, very few became fossils. Today we have relatively little evidence left from this time. The Paleozoic Era is the age of ancient life. It starts with early sea life such as the trilobites and cephalopods and then is followed in later periods by the insects, fishes and the early amphibians and reptiles. Algae and plants grew on the land during this period, but the plants were relatively simple ferns and mosses. As plants began to produce more and more oxygen on the planet, animal life was able to grow and flourish in the new atmosphere. The third era, the Mesozoic Era (meaning middle era of life) is the Age of the Ruling Reptiles. Three main groups of reptiles, the dinosaurs, crocodiles and pterosaurs were the dominant forms of life throughout
