The Paleozoic Era is the earliest of three geologic eras of the Phanerozoic Eon, spanning from 541 to 252.17 million years ago. The Paleozoic was a time of dramatic geological, climatic, and evolutionary change. The Cambrian Period witnessed the most rapid and widespread diversification of life in Earth's history in which most modern phyla first appeared. Fish, arthropods, amphibians, anapsida, synapsida, euryapsida and diapsida all evolved during the Paleozoic. Great forests of primitive plants covered the continents, many of which formed the coal beds of Europe and eastern North America. The Paleozoic Era ended with the largest mass extinction in Earth's history, the Permian-Triassic extinction event. The effects of this catastrophe were so devastating that it took life on land 30 million years into the Mesozoic Era to recover. Recovery of life in the sea may have been much faster.