The foundations for animal life had now been laid down, and following the appearance of mouths and mobility, evolution took off. Attenborough explores the Burgess Shale in Canada’s Rocky Mountains, where there is fossil evidence of an event 542 million years ago which saw animals increase in number, diversity and size as never before. These ancient rocks reveal the world’s first large predator, the first defences and the emergence of an animal group that would conquer the oceans: the hard-shelled arthropods.
With bodies completely covered in a hard skeleton, arthropods resisted predation and diversified beyond comparison. Attenborough examines fossils from the deserts of Morocco and beaches of Scotland which document how this group would proliferate to conquer the oceans and make the pioneering first steps onto land. Some grew large and ponderous, and others developed wings and took to the air for the first time.
It wasn’t just the arthropods that made the move onto land. A tiny, almost insignificant fossil reveals a worm-like animal which could be the ancestor of us all. From such creatures evolved the first fish, some of which would evolve lungs and slither onto land, giving rise to the amphibians. From these terrestrial beginnings the reptiles would evolve, and eventually, much later, the birds and mammals.
During the course of the history of life, not all groups were successful. Many of the earliest animals died out, leaving no living descendents. But from the earliest life, a few groups of animals endured and evolved into the wondrous diversity of life we see on Earth today. As Attenborough concludes, the first animals may seem to us very remote and strange, but all of us alive today owe our very existence to them.