The paleozoic era was a period of time 251-542 million years ago. During the paleozoic era, vertebrates (animals with backbones) began to diverge. A number of various organisms were found for the first time; tetrapods, insects, and the first vascular plants appeared around this time. An explosion of different types of animals occurred during the paleozoic -- the land was colonized by plants and invertebrates as well.
At the end of the paleozoic era a mass extinction took place.
