Query: A large number of ancient mass extinction events have been strongly linked to global climate change.

Relevant passages:
Quaternary extinction event <=SEP=> The Quaternary period saw the extinctions of numerous predominantly larger , especially megafaunal , species , many of which occurred during the transition from the Pleistocene to the Holocene epoch . However , this extinction wave did not stop at the end of the Pleistocene , but continued , especially on isolated islands , in human-caused extinctions , although there is debate as to whether these should be considered separate events or part of the same event . Among the main causes hypothesized by paleontologists are natural climate change and overkill by humans , who appeared during the Middle Pleistocene and migrated to many regions of the world during the Late Pleistocene and Holocene . A variant of the latter possibility is the second-order predation hypothesis , which focuses more on the indirect damage caused by overcompetition with nonhuman predators . The spread of disease is also discussed as a possible reason .

Cretaceous–Paleogene extinction event <=SEP=> The Cretaceous -- Paleogene ( K -- Pg ) extinction event , also known as the Cretaceous -- Tertiary ( K -- T ) extinction , was a mass extinction of some three-quarters of the plant and animal species on Earth that occurred over a geologically short period of time approximately 65 million years ago . With the exception of some ectothermic species like the leatherback sea turtle and crocodiles , no tetrapods weighing more than 25 kg survived . It marked the end of the Cretaceous period and with it , the entire Mesozoic Era , opening the Cenozoic Era that continues today .   In the geologic record , the K -- Pg event is marked by a thin layer of sediment called the K -- Pg boundary , which can be found throughout the world in marine and terrestrial rocks . The boundary clay shows high levels of the metal iridium , which is rare in the Earth 's crust but abundant in asteroids .   As originally proposed in 1980 by a team of scientists led by Luis Alvarez , it is now generally thought that the K -- Pg extinction was caused by a massive comet or asteroid impact , estimated to be 10 km wide , 66 million years ago and its catastrophic effects on the global environment , including a lingering impact winter that made it impossible for plants and plankton to carry out photosynthesis . The impact hypothesis , also known as the Alvarez hypothesis , was bolstered by the discovery of the 180 km Chicxulub crater in the Gulf of Mexico in the early 1990s , which provided conclusive evidence that the K -- Pg boundary clay represented debris from an asteroid impact . The fact that the extinctions occurred at the same time as the impact provides strong situational evidence that the K -- Pg extinction was caused by the asteroid . It was possibly accelerated by the creation of the Deccan Traps . However , some scientists maintain the extinction was caused or exacerbated by other factors , such as volcanic eruptions , climate change , or sea level change , separately or together .   A wide range of species perished in the K -- Pg extinction . The best-known victims are the non-avian dinosaurs . However , the extinction also destroyed a plethora of other terrestrial organisms , including certain mammals , pterosaurs , birds , lizards , insects , and plants . In the oceans , the K -- Pg extinction killed off plesiosaurs and the giant marine lizards ( Mosasauridae ) and devastated fish , sharks , mollusks ( especially ammonites , which became extinct ) and many species of plankton . It is estimated that 75 % or more of all species on Earth vanished . Yet the devastation caused by the extinction also provided evolutionary opportunities . In the wake of the extinction , many groups underwent remarkable adaptive radiations -- a sudden and prolific divergence into new forms and species within the disrupted and emptied ecological niches resulting from the event . Mammals in particular diversified in the Paleogene , producing new forms such as horses , whales , bats , and primates . Birds , fish and perhaps lizards also radiated .