A species goes extinct when it can no longer survive and reproduce in its environment and cannot move to a new one.
Mass extinctions are large worldwide decreases in biodiversity, when rates of extinction exceed rates of speciation. Mass extinctions are generally caused by geological or astronomical events, such as volcanic eruptions, changes in atmospheric composition, sea level rise or fall, global cooling and warming, and asteroid impacts.
The Permian-Triassic extinction is the largest known mass extinction event, also known as “The Great Dying” or the “Permian-Triassic Disaster”. It took place approximately 252 million years ago at the end of the Permian period, driving over 90% of all species to extinction.
Cretaceous-Palaeogene (K-Pg) or Cretaceous-Tertiary (KT) Extinction occurred approximately 66 million years ago and is most famous for driving the dinosaurs to extinction, while wiping out 75% of all other species. Nevertheless, some species, including mammals and amphibians, benefited from the opening of previously occupied niches.
Many scientists agree that a massive asteroid impact on the Yucatan Peninsula of Mexico was the most important cause of the event, which led to geologic instability in certain areas, triggering earthquakes, volcanic activity, sea level rise, and massive fires.
