T. Rex and the Crater of Doom

T. Rex and the Crater of Doom is a 1997 book by American geologist and author Walter Alvarez. Now a well-known figure in his field, Alvarez was among the first geologists to hypothesize that the mass extinction of the dinosaurs during the late Cretaceous period was caused by an asteroid impact. In this work, Alvarez recounts forming his initial hypothesis and research questions and collaborating with other professionals in a hunt for evidence. Alvarez’s research dramatically changed scientists’ understanding of Earth’s history by revealing how one rare, catastrophic event plunged Earth into chaos and resulted in a mass extinction event that ended the dinosaur age. T. Rex and the Crater of Doom was originally published by Princeton University Press in 1997.

This guide refers to the Kindle edition of the work, which was published in 2013.

Summary

In his 2008 Foreword, American science journalist Carl Zimmer explains how Walter Alvarez’s research profoundly impacted geologists’ understanding of Earth’s past. The impact hypothesis was unpopular among many geologists in the 1970s and 1980s, since they strongly believed that Earth was formed through gradual, cumulative changes. By finding evidence that supported his theory, Alvarez prompted scientists to become more aware of the role that catastrophic change has played in Earth’s history.

In his Preface, Alvarez explains that by the late 20th century, scientists had learned that uniformitarianism (development through gradual changes) and catastrophism (sudden changes resulting from catastrophes) both help explain Earth’s history. He argues that interdisciplinary collaboration among scientists yields better research and a more holistic understanding of Earth.

In Chapter 1, “Armageddon,” Alvarez details the asteroid impact that resulted in the Chicxulub crater on Mexico’s Yucatan peninsula. The text describes the asteroid’s size and speed and the many short- and long-term consequences of its impact, revealing that the event triggered the rapid die-off of every non-avian dinosaur species, ending their 150-million-year existence and the Cretaceous period. Chapter 2, “Ex Libro Lapidum Historia Mundi,” explains how scientists interpret the stratigraphy of rock layers and outlines the different methods they use to date rocks and fossils. While researching exposed limestone in Gubbio, Italy, in the 1970s, Alvarez noticed the stark contrast in rock layers from the Cretaceous period (at the end of the Mesozoic era), which contained many tiny marine fossils, and rock layers from the subsequent Tertiary period (at the beginning of the Cenozoic era), which had very few. These observations fueled his impact hypothesis that a catastrophic event may have occurred that abruptly killed off sea life.

Chapter 3, “Gradualist versus Catastrophist,” details two main schools of thought in geology. Early geologists tended toward catastrophism, believing that sudden, disastrous events largely shaped Earth, while later geologists embraced the gradualist view that Earth developed through gradual geological and evolutionary processes. In Chapter 4, Alvarez recounts how he considered different catastrophic explanations for the dinosaurs’ die-off, including a supernova explosion near Earth, which would have created lethal radiation. However, after he and his team identified higher levels of iridium in the rock layers dating to the late Cretaceous period, Alvarez formed his impact hypothesis, arguing that an asteroid collided with Earth and triggered the mass extinction event.

In Chapter 5, “The Search for the Impact Site,” Alvarez describes how he and his colleagues scoured the globe for impact sites large enough and old enough to be the “crater of doom.” He recalls his confusion upon finding clues that the crater should be in the ocean, when in reality it was on land adjacent to the ocean.

Chapter 6, “The Crater of Doom,” describes his joy upon finding the impact crater, Chicxulub, with his colleagues. He explains the different types of evidence, such as spherules and impact-melt rocks, which date the crater to the time of the late Cretaceous period and confirm that it was created by an asteroid impact.

Chapter 7, “The World After Chicxulub,” argues that the discovery and study of the impact crater ended extreme gradualism in geology by revealing the important role of catastrophes in shaping Earth. Alvarez reveals that Earth scientists continue to study ancient impacts, volcanism, and mass extinctions to better understand the planet’s history.