Dinosaurs - Geology: the Cretaceous - Tertiary boundary (KT boundary). Location: Red Deer River Valley, north of Drumheller, Alberta, Canada. Sixty five million years ago an asteroid or comet collided with Earth at the tip of the Yucatan Peninsula. The material ejected from Earth as a result of the impact (pulverised terrestrial rocks and pulverised fragments of the bolide) fell back to earth, forming a thin layer that has been found at many sites around the world. It is usually a one to two-centimeter thick layer of clay, rich in the element iridium. Many paleontologists think the global catastrophy triggered by the impact caused the extinction of the dinosaurs as well as of many marine reptiles and invertebrates. On this photograph the boundary clay layer is indicated by the bottom tip of the pen.