1. Dinosaur extinct

2. The nemesis theory is one of many "It came from outer space" theories of dinosaur extinction. The idea is that a comet comes close to the earth every 26 million years and brings with it lots of debris that hits the planet, changes the weather and kills off lots of animals. 65 million years ago it might have killed off dinosaurs, pterosaurs and big marine reptiles. A related theory, that asteroids cause extinctions, has evidence in a big asteroid crater found lately in Mexico from 65 million years ago. But we don't know if that was enough to do in the dinosaurs or if it happened after the dinosaurs were already on the way out or entirely gone. The truth is, we don't what caused dinosaur extinction and it might have been a combination of things like asteroids, volcanoes, gradual climate changes, and even disease.

3. It's a mystery! (Don Lessem) Dinosaurs became extinct at the end of the Cretaceous period, approximately 65 million years ago. While some scientists think a large asteroid killed off the dinosaurs (also known as the impact theory), many paleontologists feel that climate change due to a drop in sea level might have been responsible. I think the extinction question is still unresolved, but I am not a strong believer in the impact theory. (Bill Hammer) I really don't know. What makes you so sure that dinosaurs really are extinct? Seems like everyone wants to know why dinosaurs went extinct. But there is a group of scientists who seriously argue that not all dinosaurs went extinct 65 million years ago. Of course triceratops and T. rex did die out. But there is also a lot of evidence to suggest that modern birds evolved from the carnivorous theropod dinosaurs. I

4. If this is true, if dinosaurs have living descendants, is it entirely fair to say that the dinosaurs are extinct? The latest news flashes from the journal Science point to volcanic eruption as an important mechanism in mass extinctions. One group of scientists has discovered that there was a huge episode of eruption in what is now Siberia at the beginning of the Mesozoic - a time in earth's history when there was an extinction even greater than the one at the end of the Mesozoic that killed many of the dinosaurs. A second group of scientists has looked at the recent death of some coral reefs and discovered that volcanic dust from an eruption far away was responsible. This doesn't necessarily mean that the extinction at the end of the Cretaceous was in fact caused by volcanic eruptions, but it makes that idea a lot stronger.