ocr: Back 12 10 (8)/(7) X 6) - - 700: - 600m years ago 500m years ago 550m years ago 900 million 700 million 550 million 500 million 475 million 450 million 425 million 800m years ago 550m years ago 480m years ago 600m years ago 440m years ago Paleozoic 570myal to 248imyal Cambrian Urdovician Silurian 570/myal to 492imya) 492/myal to 435(mya) 435(myal to 412imyal
