"Paleozoic" literally translates as the "time of ancient life" and the Era started with a remarkable increase in the complexity of animal life.

During the beginning of the Early Paleozoic continents were flooded by shallow seas and life was entirely confined to the oceans. It was a profound period for life on Earth, when almost all major animal phyla appeared within an interval of as little as 10 million years. This sudden appearance of a spectacular diversity of life forms has been termed the "Cambrian Explosion of Life".