过去曾有多次,一切生命存在的形式都从地球上消亡了。这种最可怕的大规模灭绝之一发生在六千五百万年前,当时包括恐龙在内的种类极多的动植物突然消失了。这个大灾难的起因是什么? 根据一个被认为是“碰撞理论”的主要假设,祸首是某个陨星或彗星之类的地外物体。而加利福尼亚大学伯克利分校的物理学家理查德·马勒及其同事提出了一个更有趣的理论:一颗“死星”环绕 Many times in the past, all forms of existence have disappeared from the earth. One of the most horrific mass extinctions occurred 65 million years ago, when a great variety of flora and fauna including dinosaurs suddenly disappeared. What is the cause of this catastrophe? According to one of the main assumptions that are considered “collision theory,” the culprit is the extraterrestrial object such as a meteorite or comet. Richard Murphy, a physicist at the University of California, Berkeley, and his colleagues put forward a more interesting theory: a “dead star” around