Cretaceous–Paleogene extinction event Cretaceous–Paleogene extinction event The Cretaceous–Paleogene (K–Pg) extinction event, also known as the Cretaceous–Tertiary (K–T) extinction, was a sudden mass extinction of some three-quarters of the plant and animal species on Earth, approximately 66 million years ago. With the exception of some ectothermic species such as the leatherback sea turtle and crocodiles, no tetrapods weighing more than survived. It marked the end of the Cretaceous period and with it, the entire Mesozoic Era, opening the Cenozoic Era that continues today. In the geologic record, the K–Pg event is marked by a thin layer of sediment called the K–Pg boundary, which can
Geology of Arizona The subduction of the Farallon Plate beneath western North America remains a poorly understood event, although new seismic and computer tomography modeling is shedding light on the event. As the oceanic plate subsided under North America, it generated partial melting conditions that formed volcanoes on the surface in California and Arizona. Volcanic activity commenced in western Arizona around 205 million years ago, kicking off the Nevadan orogeny, which lasted until 145 million years ago, spanning the Triassic into the Jurassic. Granite intrusions 190 million years ago enriched many veins with minerals and generated copper porphyry gold deposits. Bisbee, Arizona, 92