Geologic Time Scale

Time Periods Eons Eras Periods Epochs

Precambrian Era Time Period: 4.54 billion to 544 million years ago Earth formed from planetary nebula Organisms: First cells ( 3.9 bya) Blue-green algae & stromatolites (3.6 bya) Oldest fossilized bacteria (3.25 bya) Oldest fossilized cells w/ nucleus (2.1 bya) First multi-celled organisms (1.5 bya) First marine worms & jellyfish (670 mya)

Paleozoic Era: Cambrian Period Time Period: begins 544 million years ago Organisms: Burgess Shale First animals with hard parts (trilobites)

Paleozoic Era: Ordovician Period Time Period: began 505 million years ago Organisms: First fish First fossil evidence of land plants

Paleozoic Era: Silurian Period Time Period: Began 438 million years ago Organisms: First vascular land plants Oldest lung fish fossils

Paleozoic Era: Devonian Period Time Period: Began 408 million years ago Organisms: Oldest fossil evidence of mosses (408 mya) First insects (beetles), scorpions, and centipedes (385 mya) First lobe-finned fish (380 mya) First land animals (amphibians) (375 mya) First sharks (370 mya) First seed plants (ferns) (365 mya)

Paleozoic Era: Mississippian Period Time Period : Began 360 million years ago Organisms: First possible reptiles (330 mya)

Paleozoic Era: Pennsylvanian Period Time Period: Began 320 million years ago

Paleozoic Era: Permian Period Time Period: Began 286 million years ago Organisms: Sail-backed reptiles End of Paleozoic– 96% of all life on Earth perishes

Mesozoic Era: Triassic Period Time Period: Began 245 million years ago Organisms: First crocodiles (240 mya) First dinosaurs (228 mya) Eoraptor and Saltoposuchus First mammals (shrew-like) (221 mya) First turtles (210 mya)

Mesozoic Era: Jurassic Period Time Period: Began 208 million years ago Organisms: Dilophosaurus (195 mya) First bird- Archeopteryx (155 mya) Apatosaurus and Brachiosaurus (152 mya) Allosaurus (carnivore) (150 mya) Stegosaurus (plate-backed dinosaur) (148 mya)

Mesozoic Era Cretaceous Period Time Period: Began 144 million years ago Organisms: First flowering plant (115 mya) Duck-billed dinosaurs (82 mya) Protoceratops (first dinosaur eggs discovered) (80 mya) Triceratops (75 mya) Tyrannosaurus rex & Velociraptor (70 mya) Ended Mesozoic with meteorite

End of Mesozoic Era

Cenozoic Era Tertiary Period Time Period: Began 65 million years ago Organisms: First ancestors of dogs & cats (64 mya) Grasses become widespread (60 mya) First ancestors of pigs & deer (57 mya) First horses (Eohippus) (55 mya) First ancestors of rabbits (45 mya) First monkeys (39 mya) Oldest human like ancestors (hominids) (4 mya)

Cenozoic Era Quaternary Period Time Period: Began 2 million years ago 1st of 4 ice ages (1 mya) Organisms: Oldest direct human-ancestor fossil Homo habilis (1 mya) First modern man, Homo sapiens (0.1 mya) Mammoth & mastodon bones (0.05 mya)