Final answer:
A mass extinction event at the end of the Cretaceous period led to the change from the Age of Reptiles to the Age of Mammals. Mammals survived this event due to their adaptations and were able to radiate into many different species.
Step-by-step explanation:
The major event that led to the change from the Age of Reptiles to the Age of Mammals was a mass extinction event at the end of the Cretaceous period. This event was caused by a large meteor impact and volcanic activity, which resulted in the extinction of the dominant dinosaurs and the rise of mammals. The climatic outcome of this event was a period of darkness and falling temperatures due to the impact and the ash ejected into the atmosphere, leading to the death of plants and subsequent starvation of herbivores and carnivores.
Mammals survived this event because they had certain adaptations that allowed them to better cope with the changing environment. Unlike dinosaurs, mammals were warm-blooded, which meant they could regulate their body temperature internally and survive in colder conditions. Additionally, mammals were generally smaller in size compared to dinosaurs, allowing them to find food and shelter more easily during periods of scarcity.