Mesozoic the Phanerozoic Eon, preceded by the Paleozoic ("ancient life") and succeeded by the Cenozoic ("new life"). The era is subdivided into three major periods: the Triassic, Jurassic, and Cretaceous, which are further subdivided into a number of epochs and stages. The era began in the wake of the Permian–Triassic extinction event, the largest well-documented mass extinction in Earth's history, and ended with the Cretaceous–Paleogene extinction event, another mass extinction whose victims included the non-avian dinosaurs. The Mesozoic was a time of significant tectonic, climate and evolutionary activity. The era witnessed the gradual rifting of the supercontinent Pangaea into separate landmasses
Intermontane Islands Intermontane Islands The Intermontane Islands were a giant chain of active volcanic islands somewhere in the Pacific Ocean during the Triassic time beginning around 245 million years ago. They were 600 to long and rode atop a microplate known as the Intermontane Plate. Over early Jurassic time the Intermontane Islands and the Pacific Northwest drew closer together as the continent moved west and the Intermontane Plate subducted. About 180 million years ago in the Mid-Jurassic time the last of the Intermontane Plate subducted and the Intermontane Islands collided with the Pacific Northwest, forming parts of British Columbia, Canada. The Intermontane