This category is for time periods not explicitly defined by years.
“The Cretaceous Period was a period in Earth's history when large dinosaurs dominated the...Cretaceous Period
“The Pleistocene era, more commonly known as the Ice Age, lasted from about 2586000 B.C. to 9700...Pleistocene
“The Ice Age was a time period visited by Biff Tannen while he stole one of the Institute of...The Ice Age