Final answer:
The K-T Boundary comes from the Cretaceous (K) and Tertiary (T) periods, marking a major mass extinction event 66 million years ago, characterized by a layer rich in iridium.
Step-by-step explanation:
The name K-T Boundary is derived from the boundary layer found in rock strata that marks the end of the Cretaceous period (denoted by the letter 'K', from its German translation 'Kreidezeit') and the beginning of the Tertiary period, which is now often called the Paleogene period (the 'T' stands for Tertiary). This boundary is significant in Earth's history as it coincides with the mass extinction event that occurred around 66 million years ago, which led to the demise of the dinosaurs and many other forms of life. The K-T Boundary is characterized by a thin layer of clay rich in iridium, a rare element that is more abundant in cosmic materials such as meteorites than in the Earth's crust. The presence of iridium has led scientists to the theory that a large asteroid impact may have caused the mass extinction event. This boundary layer provides a stark demarcation in the geological record, which is one reason why it has been intensively studied and is well-known.