Part three: the rise of animals

420 million years ago to 7 million years ago

The third section in our 14-part summary of the story of our planet and its inhabitants begins at the stage in pre-history when two great families of animals emerged from the seas and adapted to life on land.

Arthropods (eg, insects, spiders and crustaceans) and vertebrates (creatures descended from fish) combined to complete the terrestrial ecosystem. Then reptiles evolved a technique for reproducing away from the water's edge by using hard-shelled amniotic eggs. So powerful was this technology that these creatures became the dominant force of life on land, ushering in a 170-million-year era of dinosaurs – monsters that have fascinated scientists ever since their fossils were first discovered in the early 19th century.

Another group, the mammals, evolved in the shadows of the dinosaurs – before rising themselves to dominance after a terrible asteroid impact wiped out 75 per cent of all land life, including the dinosaurs, 65.5 million years ago. Meanwhile, as the Earth's crusts shifted across the globe, the climate cooled and mammals radiated to all corners of the land. Some migrated back into the seas (whales, dolphins, sea cows) while others took to the trees (monkeys) and then, by about 11 million years ago, came back down to live in the world's ever-expanding grasslands (gorillas).

This booklet, in other words, takes us to the moment when the stage is set for the entrance of the main protagonist in our two-week series: humans – whose evolution, achievements, follies and fluctuating fortunes form the subject matter of the remaining instalments (available with The Independent and The Independent on Sunday over the next 11 days and online at independent.co.uk/historyoftheworld).