阿尔瓦雷斯关于K-Pg灭绝的假说

The Alvarez hypothesis, published in the journal Science in 1980, provided a compelling, testable explanation for one of the most profound mysteries in paleontology: the sudden disappearance of dinosaurs. Geologist Walter Alvarez was studying a thin layer of clay at the K-Pg boundary in Gubbio, Italy, which marked the dramatic shift in the fossil record. To determine the rate of deposition of this clay, he consulted his father, Nobel laureate physicist Luis Alvarez. They decided to measure the concentration of iridium in the layer. Iridium is a siderophile (iron-loving) element, and most of Earth’s supply sank to the core during planetary differentiation. However, it is much more abundant in asteroids and comets. They expected a very low concentration but found levels hundreds of times higher than the background level in Earth’s crust. This iridium spike was subsequently found at the same geological boundary all over the world.

The team calculated that an asteroid approximately 10 to 15 kilometers in diameter would be required to deposit this amount of iridium globally. Such an impact would release energy equivalent to billions of atomic bombs, triggering a cascade of devastating environmental effects. These would include a massive heat pulse from re-entering ejecta, global wildfires, and an “impact winter” caused by dust and aerosols blocking sunlight, leading to the collapse of 光合作用 and food chains. The hypothesis was initially met with skepticism from many paleontologists who favored more gradual causes like volcanism or 气候变化然而，其他撞击证据的发现，如冲击石英和玻璃陨石，以及 20 世纪 90 年代初在墨西哥海岸附近发现的巨大希克苏鲁伯陨石坑，提供了压倒性的证实，并巩固了该假说作为 K-Pg 灭绝事件的主要解释。