Teacher : - As you know, many of the animals that existed in the past have become extinct; that is, they have disappeared from the face of the earth, mostly as a result of human activities. Student : - Is it only human activities that have caused the extinction of animals? Teacher : - ---- Student : - I think dinosaurs could be an example of such extinct species. I read in a science magazine that they became extinct when a huge meteor hit the earth, millions of years before humans existed.