Final answer:
The Cretaceous-Paleogene mass extinction was most likely caused by the impact of a large asteroid, as indicated by a worldwide layer of iridium, shocked quartz, and a matching crater, which led to drastic environmental and climate changes.
Step-by-step explanation:
The mass extinction event that occurred approximately 65 million years ago, known as the Cretaceous-Paleogene (K-Pg) extinction, is widely believed to have been caused by the impact of a large asteroid in the Yucatán Peninsula. The evidence supporting this includes a layer of iridium-rich sediment worldwide, shocked quartz crystals, and a massive crater in the mentioned location. These findings corroborate the hypothesis that the asteroid impact led to significant environmental changes, such as blocking sunlight, cooling the planet, and disrupting food chains, which collectively led to the mass extinction of many species, including the non-avian dinosaurs.
Paleontologists analyzing the fossil record have confirmed the rapid decline in biodiversity during this period, consistent with the devastation an asteroid impact would cause. Furthermore, there is consensus based on geological evidence which includes the boundary layer containing an unusual amount of iridium, a rare element on Earth's crust but common in asteroids, and the Chicxulub crater which aligns with the timing of the extinction event. This catastrophic event marks the division between the Mesozoic and Cenozoic eras, profoundly shaping the subsequent evolution of life on Earth.