When did the Permian-Triassic extinction event occur?

The Permian-Triassic extinction event, often referred to as the "Great Dying," occurred approximately 250 million years ago. This event marks the boundary between the Permian and Triassic geological periods and is known as the most significant extinction event in Earth's history, where around 90-96% of marine species and a large number of terrestrial species went extinct. The extinction was likely caused by a combination of factors, including volcanic activity, climate change, and changes in ocean chemistry.

The timing of this event is crucial for understanding the evolutionary history of life on Earth, as it paved the way for the dominance of dinosaurs and other forms of life in the Triassic period that followed. Each of the other dates provided in the choices corresponds to different significant geological events, such as the Cretaceous-Paleogene extinction (65 million years ago) that famously led to the extinction of the dinosaurs, or the Ordovician-Silurian extinction (439 million years ago), which impacted marine life but occurred much earlier than the Permian-Triassic event. The 199 million years ago date marks the end of the Triassic period, following the mass extinctions that shaped the preceding era.