How many species have gone extinct in each mass extinction event?
a. Permian-Triassic extinction event: 95% of marine species and 70% of terrestrial species
b. Triassic-Jurassic extinction event: About 20% of marine families and 50% of marine genera
c. Cretaceous-Paleogene extinction event: 75% of species, including dinosaurs
d. Holocene extinction event: Numerous species, particularly due to human activity
