PROF. WALTER ALVAREZ / SCIENCE PHOTO LIBRARY PROF. WALTER ALVAREZ / SCIENCE PHOTO LIBRARY
K/T boundary layer. View of the boundary layer made of clay containing iridium, between older Cretaceous (K) and younger Tertiary (T) rocks. This is known as the K/T boundary layer. It is two centimetres thick and here marked by a coin. At this locality, the layer is separated by two beds of marine limestone. The K/T layer, a phenomenon worldwide, is thought to be associated with ejected material from the impact of a large extraterrestrial object (comet or meteorite) around 65 million years ago. It has been proposed that this impact event may have been the cause of the extinction of the dinosaurs. Photographed near Gubbio, Italy.
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