The extinction of dinosaurs is one of the most dramatic mass extinctions that the Earth has ever seen. The fossil record shows that for the first 175 million years of their existence, dinosaurs took on a huge variety of forms as the environment changed and new species evolved that were suited to these new conditions. Dinosaurs that failed to adapt went extinct. However, around 66 million years ago, over a relatively short time, dinosaurs disappeared completely (except for birds), and many other animals also died out, including pterosaurs, large marine reptiles, and ammonites. Scientists believe that a sudden catastrophic event sealed their fate - something that caused unfavorable changes to the environment to occur more quickly than dinosaurs and other creatures could adapt.
The leading theory is that a huge asteroid or comet slammed into Earth 65 million years ago, blocking sunlight, changing the climate, and setting off global wildfires. The dinosaur-killing crash threw huge amounts of debris into the air and caused massive tidal waves to wash over parts of the American continents. There is also evidence of substantial fires from that point in history. The asteroid was the final, killer blow, and the last non-bird dinosaurs were living at a time of environmental change, some of which began millions of years before they went extinct.
Other theories suggest that volcanic activity, disease, or a supernova may have contributed to the extinction of dinosaurs. However, the asteroid impact theory is the most widely accepted explanation among scientists.
