Pliocene Epoch, the geologic epoch that began about 6,000,000 years ago and lasted about 4,000,000 years. It is a subdivision of the Tertiary Period of the Cenozoic Era. Great uplifting occurred in the mountains of the northwestern United States during the Pliocene Epoch. Pliocene formations in California are sources of petroleum.
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?