The extinction of dinosaurs is one of the most dramatic mass extinctions Earth has ever seen. 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, 66 million years ago, over a relatively short time, dinosaurs disappeared completely (except for birds) . Many other animals also died out, including pterosaurs, large marine reptiles, and ammonites. Although the number of dinosaur species was already declining, this suggests 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 exact nature of this catastrophic event is still open to scientific debate. Evidence suggests an asteroid impact was the main culprit. The asteroid impact caused a global catastrophe, throwing huge amounts of debris into the air and causing massive tidal waves to wash over parts of the American continents. There is also evidence of substantial fires from that point in history. The Alvarez hypothesis, named after the father-and-son duo Luis and Walter Alvarez, proposed the notion that a meteor the size of a mountain slammed into Earth 66 million years ago, filling the atmosphere with gas, dust, and debris that drastically altered the climate. Their key piece of evidence is an oddly high amount of the metal iridium in what’s known as the Cretaceous-Paleogene, or K-Pg, layer—the geologic boundary zone that seems to cap any known rock layers containing dinosaur fossils.
Volcanic eruptions that caused large-scale climate change may also have been involved, together with more gradual changes to Earths climate that happened over millions of years. Some researchers believe that emissions from the volcanoes, which released gases like sulfur dioxide and carbon dioxide, weakened the ecosystem so that dinosaurs went extinct more easily when the asteroid hit. However, a new study suggests that ancient volcanic eruptions didnt play a role in the mass extinction that killed off the dinosaurs. Whatever the causes, the huge extinction that ended the age of the dinosaur left gaps in ecosystems around the world. These were subsequently filled by the only dinosaurs to survive - birds - and mammals, both of which went on to evolve rapidly.
