Final answer:
The End-Permian Mass Extinction occurred around 251 million years ago, marking the demise of approximately 96% of marine and 70% of terrestrial species, likely due to massive volcanic activity that caused global warming and ocean anoxia.
Step-by-step explanation:
When Did the End-Permian Mass Extinction Occur?
The End-Permian Mass Extinction, which is considered the most severe mass extinction event in Earth's history, occurred approximately 251 million years ago. It marked the transition from the Permian period to the Mesozoic era. During this catastrophic event, an estimated 96 percent of all marine species and 70 percent of terrestrial species were wiped out, including the complete extinction of the trilobites.
One of the major hypotheses for the cause of the extinction is massive volcanic activity, which could have induced global warming and resulted in anoxic oceans, incapable of supporting marine life. This led to a dramatic change in Earth's biodiversity and had a profound impact on the course of evolution. It took nearly 30 million years for terrestrial tetrapod diversity to recover after this catastrophic event.
The Permian period climate was extremely dry and witnessed periods of high temperatures due to the formation of the supercontinent Pangaea. Both terrestrial and marine ecosystems were dramatically altered due to the extinction event, which remains one of the key inflection points in the history of life on our planet.