when was the cambrian period
The Cambrian Period (543 to 505 million years ago) is the first time period of the Paleozoic Era. It is preceded by the Precambrian. The Cambrian Period opened in the aftermath of a mass extinction.During the last 100 million years of the Precambrian, a unique fauna had developed.arly in the Cambrian Period the first bivalves and arthropods appeared followed by the first mollusks, brachiopods, and trilobites. During the Cambrian Period, all but one of the major groups of animals evolved during a period of 40 million years.