kt boundary sample

The KT (Cretaceous-Tertiary) boundary layer—now officially termed the K-Pg boundary—is a thin, globally distributed band of sedimentary rock dating back approximately 66 million years. It marks the precise geological dividing line between the Mesozoic and Cenozoic eras and corresponds with one of the most famous extinction events in Earth's history, wiping out non-avian dinosaurs and roughly 75% of all species.

The boundary layer is most famous for its extraordinarily high concentrations of iridium. Because this rare metallic element is abundant in asteroids but scarce in Earth's crust, its global presence provides physical evidence for the Alvarez hypothesis: a cataclysmic asteroid impact that struck the modern-day Yucatan Peninsula and created the Chicxulub crater. Alongside iridium, the clay layer contains impact-related debris such as shocked quartz and microscopic glass spheres called microtektites.