Final answer:
The mass extinction at the end of the Permian period was mainly caused by volcanic activity, while the event at the end of the Cretaceous was due to an asteroid impact.
Step-by-step explanation:
The geologic events that caused the mass extinctions at the end of the Permian and the Cretaceous periods is option a) Asteroid impact (End-Cretaceous); Volcanic activity (End-Permian). The end of the Cretaceous period approximately 65 million years ago is known for the mass extinction event that wiped out the dinosaurs and many other species. This was largely due to a cataclysmic asteroid impact near what is now the Yucatán Peninsula, which led to a significant disruption in the Earth's climate and ecosystems.
At the end of the Permian period, about 251 million years ago, the largest mass extinction in Earth's history occurred. The main suspect for this catastrophic event is prolonged and extensive volcanic activity in Siberia, which caused a runaway global warming effect and made the oceans anoxic, leading to the loss of around 96 percent of all marine species and 70 percent of terrestrial species.