The Paleozoic's starting line is a burrow in Newfoundland
The Paleozoic, the era of 'ancient life', began 538.8 million years ago and closed with the worst extinction in the history of complex life. Its official start is pinned not to a skeleton but to a trace: the burrows of an unknown creature called Treptichnus pedum, preserved in rock at Fortune Head, Newfoundland.
Adam Sedgwick coined the name in the 1830s for the Cambrian and Ordovician, and John Phillips stretched it in 1840 to cover everything through the Permian. It comes from Greek words for old and life. The era's six periods run from the Cambrian to the Permian, ending 251.9 million years ago when the Mesozoic began.
Pinning down its base proved tricky. Sedgwick drew the line at the first trilobites, but older complex life kept turning up. Small shelly fossils were used for a while, yet most rocks of that age are sandstones and mudstones that rarely preserve skeletons. So the International Commission on Stratigraphy turned to trace fossils, which grow more complex as their makers do, and after two decades of debate chose the Newfoundland site. The top boundary sits near Meishan in southern China, marked by the first appearance of a tiny conodont, Hindeodus parvus, and dated with remarkable precision.
Life changed beyond recognition. The Cambrian explosion produced almost all modern animal body plans, including molluscs, brachiopods and trilobites, while land remained bare. In the Ordovician, arthropods first ventured onto the empty continent of Gondwana, and fish, cephalopods and corals appeared. Glaciation then drove the Ordovician-Silurian extinction, which killed about 60 percent of marine invertebrates. By the late Paleozoic, forests of primitive plants covered continents, later becoming the coal of Europe and eastern North America, and large synapsids and the first conifers had arrived.
The continents staged their own drama. The era opened with the supercontinent Pannotia breaking up, and early on central Africa probably lay near the pole. Gondwana assembled about 510 million years ago, and later collisions built Pangaea, raising the Appalachians and the Urals. The end-Permian catastrophe was so severe that land life took some 30 million years to recover, though the seas may have bounced back sooner.
Source: Paleozoic
