9Earth Is 18 Galactic Years Old

The solar system is zooming through interstellar space at around 500,000 miles an hour. Even at that rate, it takes about 250 million years to travel once around the Milky Way. 

The last time our 4.5-billion-year-old planet was in this same spot, continents fit together differently, dinosaurs were just emerging, mammals had yet to evolve, and the most profound mass extinction in the planet’s history—an event called the Great Dying—was in progress.