when did the cambrian era begin?
Trilobites were the dominant species during the Cambrian Period, 540 to 490 million years ago. Credit: Bill Frische | Shutterstock. View full size image. The Cambrian Period is the first geological time period of the Paleozoic Era (the âtime of ancient lifeâ). This period lasted about 53 million years and marked a dramatic burst of evolutionary changes in life on Earth, known as the Cambrian Explosion..