Mesozoic
The lower (Triassic) boundary is set by the PermianTriassic extinction event, during which approximately 90% to 96% of marine species and 70% of terrestrial vertebrates became extinct. It is also known as the "Great Dying" because it is considered the largest mass extinction in the Earth's history. The upper (Cretaceous) boundary is set at the CretaceousTertiary (KT) extinction event (now more accurately called the CretaceousPaleogene (or KPg) extinction event), which may have been caused by the impactor that created Chicxulub Crater on the Yucatan Peninsula. Towards the Late Cretaceous large volcanic eruptions are also believed to have contributed to the CretaceousPaleogene extinction event. Approximately 50% of all genera became extinct, including all of the non-avian dinosaurs.

Q: How many terrestrial species died during the extinction?
70%