Cambrian Period, the first geologic period of the Paleozoic Era. It began 570,000,000 years ago and lasted 70,000,000 years. It is named for Wales (which the Romans called Cambria), where sedimentary rocks of the period were first recognized.
Many scientists believe that the impact from a massive asteroid was what killed off the dinosaurs. It's what started the Age of Mammals. But what if the asteroid had missed?
Every time a new fossil is found, one of the first things scientists determine is how old that fossil really is. But how do they determine it, and how can they be completely accurate?