what two periods were there mass extinctions of life on earth?

Two significant periods of mass extinction on Earth include the Permian-Triassic extinction, approximately 252 million years ago, which wiped out about 90% of marine species and 70% of terrestrial vertebrates. Another major event is the Cretaceous-Paleogene extinction, around 66 million years ago, famously associated with the asteroid impact that led to the demise of the dinosaurs and about 75% of species on Earth.