Many things can kill the living plants and/or animals that reside on land or within the many bodies of water on our Earth. Such was the case for nearly all of the prehistoric animals and plants that were alive as far back as 65 million years ago.
Evidence was recently discovered of a global disaster that occurred about 65 million years ago in which few living things survived, namely some mammals and plants, whose future generations are still alive a well today. Those 65 million years ago a meteor or a comet struck the Earth and the resulting explosion caused a dust cloud that blocked the light of the Sun from reaching the surface of the Earth for many years.
Those living things that were not killed outright from the explosion died from starvation or the resulting nuclear winter that took place afterward. Cold-blooded reptiles could not survive the rapid change of the climate on those other places on Earth that were otherwise unaffected. "The Age of Reptiles" came to an end. If you have not already guessed, there was a major brake in the food chain that prevailed during that time in the history of our Earth.
Those carnivore dinosaurs died away because their food source also died. You see, the plants died and that food source for the plant eating dinosaurs caused those dinosaurs to also die. That surely was too bad for all of those cold-blooded dinosaurs. Then again, some dinosaurs did survive because their food source was the fish within the seas.
Maybe that is why the people these days are still seeing a dinosaur within a lake in the British Isles. In any event, the end result was the global mass extinction of the dinosaurs. Few reptile fossils were found in rocks that are above the level of that mass global extinction event.
On the other hand, regional mass extinction events are more common. There have been many such events that have been recorded in the past and, no doubt, they will continue to occur for as long as there are living things within our environment. For example, a disease for which there is no cure can kill all of the people with the area of its outbreak.
The spread of the "Black Plague" in Europe is such an event. So too, the spread of the A.I.D.S. virus is an ongoing threat to the survival of Humanity. That particular mutating virus already killed more than 20 million people and that number increases with each passing day. Only God knows if a cure will ever be found for it.
A regional natural disaster can also causes a mass extinction event. Such an event took place after the Mount St. Helen volcano exploded, killing nearly all of the life within the area of the explosion. Earthquakes and tidal waves have also taken their toll on millions of living things during those years gone by.
As luck would have it, global warming could also cause a global extinction event as the years continue to pass. There has been a drastic change of our Earth's climate and it is predicted to continue if Mankind continues to destroy the environment in which we all live.