The KT boundary is a significant geological marker that denotes a catastrophic event that occurred about 65 million years ago. This event is characterized by the abrupt disappearance of dinosaurs and approximately half of the planet's animal species from the fossil record. The causes of this mass extinction have been widely studied, with theories ranging from asteroid impacts to volcanic activity.

Bill Bryson discusses this momentous time in his book "A Short History of Nearly Everything." He highlights the profound impact this event had on life on Earth, emphasizing how it reshaped ecosystems and the evolutionary path that followed. The extinction at the KT boundary represents a critical turning point in the history of our planet.