The term 'Cambrian, for one' is referring to an ERA in Earth's history. The Cambrian period was the first period of the Paleozoic ERA, which lasted from 541 million years ago to 485.4 million years ago. During this time, many new species of animals appeared and the first complex organisms began to evolve. This period is known as the 'Cambrian Explosion' due to the rapid diversification of life that occurred during this time.