字幕列表 影片播放 列印英文字幕 When I was in grade school, my teacher taught me that about 66 million years ago a huge asteroid hit the earth right around Mexico and BAAAM. Just like that - wiped out the dinosaurs. Yeah… not true. Hello survivors, Lissette here for DNews. The mass extinction that doomed the dinosaurs is still a bit of a mystery. As with anything that happened millions of years ago, we must rely on indirect evidence to test theories about things that we can no longer directly observe or record. So there are lots of theories about how the dinosaurs died off. But one thing scientists are increasingly agreeing on is that the dinosaurs did NOT die all of a sudden. Nope, instead they died a slow, miserable, gradual death. It wasn't just the asteroid that killed them. Though it definitely played a part, there were many other factors involved. Scientists in the UK at the University of Reading and the University of Bristol think they actually started slowly dying out about 40 million years before the asteroid hit; And then, after the blast, continued to die off for millions of years after. Sure, they agree with most of our teachers that the asteroid at Chikshuhloob Mexico did indeed kill many dinosaurs through direct impact and through the tsunami it triggered. But, they argue that this was more like the straw that broke the camel's back. During the Cretaceous period, before the asteroid hit, the earth was experiencing global environmental changes that did not favor land roaming dinosaurs. It was experiencing sea level fluctuations, a period of extreme cooling, and lots of volcanic activity. This meant that dinosaurs had to move around to find food and resources where the climate was more favorable. But, it was difficult for dinos that roamed on foot because during the course of the Cretaceous period, the land itself was slowly breaking up from one large continent to many different land masses. Things were a little better for birds who could fly to places with resources, but even then, many birds species also died out. On top of that, mammals were on the rise before the asteroid - it turned out pretty good for us, given that they're our ancestors. But, scientists theorize that our small rodent looking relatives likely helped to knock dinosaurs out. They may have competed with the dinosaurs for food and other resources, eaten their eggs, or infected them with disease. Pretty big impact from such little guys. Altogether this meant that when the asteroid did hit 66 million years ago, the dinosaurs were already vulnerable to extinction. The dwindling populations could not reproduce quickly enough to survive the losses from the asteroid's impact, the tsunami and other environmental changes that ensued. Between that, the volcanoes, the fluctuating oceans, and the global cooling (not great for cold-blooded reptiles) - the dinos didn't stand a chance. The asteroid certainly had an impact, but the dinosaurs had been dying millions of years before it, and continued to die off millions of years afterward. We can't give the rock all the credit. But for more on which dinos actually survived the mass extinction. Check out Tara's video here What do you remember being taught about the dinosaurs? Did your teachers tell you the same thing I was told about their extinction?