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The Paleozoic Era, the period of geologic time from 600 million to 225 million years ago. This is the first and longest era for which an abundant fossil record exists. Hence it was give this name, The Paleozoic Era, which means "ancient life" in Greek. During this time, which covers the Cambrian through the Permian periods, the continents were subjected to repeated and widespread flooding by shallow marine incursions called epicontinental seas.
The Paleozoic is bracketed by two of the most important events in the history of animal life. At its beginning, multicelled animals underwent a dramatic "explosion" in diversity, and almost all living animal life forms appeared within a few millions of years. At the later end of the Paleozoic, the first and the largest mass extinction in history wiped out approximately 90% of all marine animal species. The causes of both these events are still unknown and is the subject of much research and controversy. Roughly halfway in the era, animals, fungi, and plants alike colonized the land, the insects took to the air.
There were six major continental land masses during this Era; each of these consisted of different parts of the modern continents. For instance, 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. These Paleozoic continents experienced tremendous mountain building along their margins, and numerous incursions and retreats of shallow seas across their interiors. Large limestone outcrops are evidence of these periodic incursions of continental seas.
Many Paleozoic rocks are economically important. For example, much of the limestone quarried for building and industrial purposes, as well as the coal deposits of western Europe and the eastern United States, were formed during the Paleozoic.
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