Introduction to the Vendian Period 650 to 544 Million Years Ago When Charles Darwin wrote On the Origin of Species, he and most paleontologists believed that the oldest animal fossils were the trilobites and brachiopods of the Cambrian Period, now known to be about 540 million years old. Many paleontologists believed that simpler forms of life must have existed before this but that they left no ...

Introduction to the Proterozoic Era 2.5 billion to 544 million years ago The period of Earth's history that began 2.5 billion years ago and ended 544 million years ago is known as the Proterozoic. Many of the most exciting events in the history of the Earth and of life occurred during the Proterozoic -- stable continents first appeared and began to accrete, a long process taking about a billion ...