A major stratigraphic boundary on Earth that marks the end of the Cretaceous Period and of the Mesozoic Era and the start of the Tertiary Period and of the Cenozoic Era. The Cretaceous-Tertiary Boundary, also known as the K-T Boundary (because the Cretaceous is traditionally represented by K), occurred about 65.5 million years ago and coincides with a mass extinction in which the last of the dinosaurs and two-thirds of all other species on Earth died out. The K-T Boundary is marked in many places by a distinctive layer of clay, often highly enriched in elements such as iridium and osmium relative to the layers above and below.
Related categories MEGACATASTROPHES
GEOLOGY AND PLANETARY SCIENCE
ORIGIN AND EVOLUTION OF LIFE
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