600 million years ago: The emergence of the first multicellular organisms.
542–488 million years ago: Cambrian period. Evolution of external skeletons leads to a great diversity of animal body plans, among them trilobites and brachiopods. First vertebrates, equipped with a notochord, precursor of the spinal column.
488–444 million years ago: Ordovician period. Great diversification of trilobites, lamp shells, gastropods and graptolites. Emergence of sea urchins, starfishes and ammonites. The end of the period sees the first evidence of land plants, and a mass extinction of many species.
444–416 million years ago: Silurian period. New forms of marine life follow the mass extinction, including scorpion-like animals and jawed fishes (at first cartilaginous, latterly bony). The first invertebrates, scorpions and wingless insects, appear on land, as do vascular plants such as club mosses.
416–359 million years ago: Devonian period. Huge coral reefs. First ferns. Emergence of primitive amphibians, the first four-legged animals, which begin to colonize land.
359–299 million years ago: Carboniferous period. First flying insects and first reptiles. Great proliferation of land plants, including conifers, which over time form extensive coal deposits.
299–251 million years ago: Permian period. Reptiles diversify. Period ends with mass extinction of many groups of marine animals, including trilobites. Many terrestrial groups also wiped out, making way for dinosaurs.
251–200 million years ago: Triassic period. Emergence of the dinosaurs on land. The first small mammals also appear.
200–145 million years ago: Jurassic period. Great diversification of the dinosaurs, turtles and crocodiles. Tropical forests. One of the first bird fossils, Archaeopteryx , appears towards the end of the period.
145–66 million years ago: Cretaceous period. Flowering plants emerge and begin to dominate on land. Grasses appear. The end of the period witnesses the sudden mass extinction not only of the dinosaurs, but also of the ammonites, ichthyosaurs and pterosaurs. Birds (descended from one group of dinosaurs) and mammals survive.
66–56 million years ago: Palaeocene epoch. Many new groups of mammals appear, including the first primates.
56–34 million years ago: Eocene epoch. Spread of mammals, including elephants, whales, rodents, carnivores and hoofed mammals.
34–23 million years ago: Oligocene epoch. Spread of grasslands, and first appearance of monkeys.
23–5.3 million years ago: Miocene epoch. Spread of horses, first appearance of apes. Many animals, such as frogs, snakes and rats, are very similar to those of today.
7 million years ago: Split between our ancestors and the ancestors of chimps and bonobos.
6 million years ago: Early humans begin to walk some of the time on their hind legs.
5.3–2.6 million years ago: Pliocene epoch. Origin of mammoths. Walking upright becomes the norm for early humans.
2.6 million years ago: Earliest evidence of human tool use.
2.6 million–11,700 years ago: Pleistocene epoch. Period of ice ages and warmer interglacial periods.
2.4 million years ago: Appearance of Homo habilis .
1.9 million–143,000 years ago: Dominance of Homo erectus .
200,000 years ago: Emergence of Homo sapiens (modern humans) in Africa, where they remain for another 100,000 or more years.
11,700 years ago–present: Holocene epoch. After the end of the last ice age, many large land animals such as mammoths become extinct. Humans come to dominate the planet.