CretaceousTertiary

The Cretaceous-Tertiary (K-T) boundary is a geological boundary marking the end of the Cretaceous period and the beginning of the Paleogene period, approximately 66 million years ago. This boundary is significant because it coincides with the Cretaceous-Paleogene (K-Pg) extinction event, one of the five major mass extinctions in Earth's history. The event is marked by a thin layer of iridium-rich clay, which is believed to be the result of an asteroid impact.

The most widely accepted theory for the K-T extinction is the Chicxulub impact hypothesis, which suggests that a large asteroid, approximately 10 kilometers in diameter, struck the Earth near the present-day Yucatan Peninsula in Mexico. The impact would have caused massive tsunamis, earthquakes, and volcanic activity, leading to a global winter and the extinction of about 75% of all species on Earth, including non-avian dinosaurs.

The K-T boundary is also notable for the discovery of the first known bird fossils, which suggest that birds may have evolved from theropod dinosaurs. The boundary is studied by geologists, paleontologists, and other scientists to better understand the causes and effects of mass extinctions and the subsequent evolution of life on Earth.