The mass extinction brought about at the end of the 50-million-year-long Permian period, brought about the end the entire Paleozoic era, in progress since the dawn of animal life. The Paleozoic, with its ancient seas filled with trilobites, brachiopods, and strange reefs, was as starkly different from the age to come as the age of dinosaurs is from our world today.
At present, our Solar System is in its twentieth orbit of the Milky Way near the inner edge of a spiral feature known as the Orion Arm or, less poetically, the Local Arm. The ghostly arms are not permanent features of a disc galaxy like the Milky Way. Rather, they are concentrations of gas and dust where stars form, produced by disturbances within the Milky Way, or on occasions by a jolt from outside, such as a supernova or the passage of the Solar System through one of the dusty gas clouds that congregate in spiral arms.