The K-Pg Boundary, also known as the Cretaceous-Paleogene Boundary, marks a significant geological event that occurred about 66 million years ago. This boundary separates the Cretaceous period, which was characterized by the dominance of dinosaurs, from the Paleogene period, which saw the rise of mammals. This event is widely believed to have been caused by a massive asteroid impact, leading to dramatic climate changes. The K-Pg Boundary is identified by a distinct layer of sediment rich in iridium, a metal that is rare on Earth but common in asteroids, providing evidence for this catastrophic event.