The Cambrian (/ˈkæmbriən/ or /ˈkeɪmbriən/) is the first geological period of the Paleozoic Era, lasting from 541.0 ± 1.0 to 485.4 ± 1.9 million years ago (mya) and is succeeded by the Ordovician. Its subdivisions, and indeed its base, are somewhat in flux. The period was established (as “Cambrian series”) by Adam Sedgwick, who named it after Cambria, the Latinised form of Cymru, the Welsh name for Wales, where Britain's Cambrian rocks are best exposed.