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Precambrian Time
4.5 billion to 542 million years ago. Ediacarans were the first multi-celled organisms. A global ice age caused massive extinctions. The molten outside of Earth cooled and formed the crust. The sea released oxygen as photosynthesis took place in organisms under the sea. -
Paleozoic Era
543 to 248 Million Years Ago. Organisms went through dramastic changes during this period. Trilobites and Brachiopods dominated the seas. The Permian extinction, 244 million years ago, devastated the marine biota: tabulate and rugose corals, blastoid echinoderms, graptolites, and most crinoids died out, as did the last of the trilobites. At the beginning of the Paleozoic, today's western coast of North America ran east-west along the equator, while Africa was at the South Pole. -
Mesozoic Era
Spans from 245 to 65 million years ago. Dinosaurs evolved in the Triassic period. Cycads and Bennettitaleans were among the dominant land vegetation. Except for birds, dinosaurs became extinct at the end of the Cretaceous. The Mesozoic was also a time of great change in the terrestrial vegetation. The early Mesozoic was dominated by ferns, cycads, ginkgophytes, bennettitaleans, and other unusual plants. -
Cenozoic Era
The Cenozoic spans only about 65 million years. Plants, insects, fish and birds evolved the most. During the Paleogene the climate worldwide was warm and tropical, much as it had been for most of the preceding Mesozoic. During the Cenozoic, the fragmentation of continental landmasses continued as the Earth's surface took on its present form.
