T. Rex and the Crater of Doom

“Impacts may not only have caused geological trauma, however. They may have seeded our planet. Comets and meteorites carry with them amino acids and other building blocks of life, and some of those raw ingredients may have survived the fall through Earth’s atmosphere. In recent years, some scientists have even proposed that impacts may have delivered living organisms from one planet to another.”

This fascinating hypothesis raises the question of how asteroid impacts may foster life by bringing the “raw ingredients” of life onto a planet from other parts of space. In this passage, journalist Carl Zimmer normalizes the reality of asteroid impacts in Earth’s history and notes how scientists continue to grapple with how such impacts may have informed Earth’s development both constructively and destructively.

“Looking back at the abyss of time which separates us from the Cretaceous, we can somehow feel nostalgia for a long-lost world, one which had its own rhythm and harmony. We feel a special sadness when we think about its plants and animals, fish and birds—for most of the Cretaceous animals and plants are irretrievably lost.”

In this description, Alvarez encourages readers to imagine the Cretaceous period’s plants and animals with affection and respect. In referring to that period’s “rhythm and harmony,” Alvarez emphasizes that it had full, functioning ecosystems that would have continued to thrive if not for the Yucatan impact. In addition, this passage primes readers to anticipate the details of the incredible destruction that the asteroid caused when it collided with Earth.

“Then, as the ground began to shake uncontrollably from the passing seismic waves, the sky itself turned lethal. Beginning with a faint glow, the sky grew more and more intensely red, passing into incandescence, growing brighter and brighter, hotter and hotter. Soon the Earth’s surface itself became an enormous broiler—cooking, charring, igniting, immolating all trees and all animals which were not sheltered under rocks or in holes.”

This vivid imagery describes the scene of the Yucatan impact moments after the asteroid collided with Earth, making this passage highly memorable. This apocalyptic scene communicates how the impact created earthquakes in conjunction with terrible forest fires and extreme heat, helping convey how many creatures died instantly. The description of these effects helps develop The Role of Catastrophes in Earth’s History as a theme.

“A world first dark and frozen, then deadly hot, a world poisoned by acid and soot. This was the global aftermath of the Yucatan impact. We wonder how anything could survive this environmental apocalypse. Yet there were survivors, and their descendants populate the world today.”

This poetic passage broadly sums up the short-term consequences of the Yucatan impact. By mentioning the survivors of this “apocalypse,” Alvarez further develops The Role of Catastrophes in Earth’s History as a theme, emphasizing that had the Yucatan impact not occurred, the evolution of certain species, such as our own, would also not have happened.

“Most of the history of our planet is written in rocks. Rocks are the key to Earth’s history, because solids remember, but liquids and gases forget. Retrieving these long-lost memories is the business of geologists and paleontologists, of people who have chosen to be the historians of the Earth.”

In this passage, the text highlights the importance of rocks in scientifically understanding Earth and its history, thus developing the theme of Rocks as Historical Records, encouraging the reader to consider rocks as, in effect, a record of natural history. By referring to geologists and paleontologists as the “historians of the Earth,” Alvarez helps demystify these professions and spark curiosity about their discoveries.

“Archaeological sites the world over display the fundamental rule of history written in rocks—younger layers rest on older ones. This is the law of superposition, the basis of all stratigraphy. Stratified rocks are deposited in succession, layer upon layer.”

In this quote, the author explains stratigraphy, conveying how layers of rock build up over time. This explanation provides crucial context for understanding Alvarez’s work in which he noticed the dramatic difference in rock layers from the Cretaceous period compared to those from the subsequent Tertiary period.

“To find out, we break off a fresh piece of Scaglia and look at it with the little magnifying hand lens all geologists carry. Tiny specks throughout the rock now resolve themselves into little coiled, chambered microfossils. These are the shells of foraminifera, the single-celled predators that float near the surface of the deep oceans, and which almost perished, although not quite, in the same mass extinction that finished off T. rex.”

This passage encourages readers to imagine themselves in Italy beside Alvarez, looking at a piece of the limestone Scaglia Rossa rock. This approach helps readers visualize the author’s experience in the field, looking at foraminifera in the rock. In referencing the dramatic die-off of foraminifera at the same time as the dinosaurs, this discussion foreshadows Alvarez’s initial hypothesis that some kind of catastrophe occurred at the end of the Cretaceous period.

“These planktic forams are particularly useful for dating rocks, because ocean currents spread newly evolved species rapidly throughout the oceans of the world, and thus evolutionary changes are immediately recorded worldwide when the forams die and their shells settle to the bottom.”

This explanation provides more context about why foraminifera are of particular interest to geologists and other scientists, and helps explain how foraminifera became ubiquitous in different rock layers around the world. This supports the theme of The Scientific Process of Discovery because Alvarez’s research on foraminifera in rock layers created the basis for his impact hypothesis.

“Bill and I learned to identify the KT boundary ourselves, and as we located this key break in outcrop after outcrop across the Apennines, we began to wonder about its significance. Why had the forams almost become extinct? What had happened to cause that extinction? And why was it so abrupt?”

Alvarez reveals how he and his colleague Bill Lowrie puzzled over the differences in rock layers from the Cretaceous and Tertiary periods, namely in their differing numbers of foraminifera. This passage bolsters the theme of The Scientific Process of Discovery as the author shows how his observations of physical evidence in the rock layers prompted his research questions and later his hypothesis.

“Natura non facit saltum—Nature does not make sudden jumps—nevertheless remained a central tenet of Darwin’s theory, and has strongly influenced paleontological thought down to the present time. Nature, it seemed to most Earth scientists, was a calm, well-regulated domain in which catastrophes and irregularities were forbidden.”

Alvarez helps convey how uniformitarianism became entrenched in the field of geology, noting how Darwin himself espoused this view because it tied in with his understanding of the gradual evolution of species. This explanation contributes to how the book contrasts uniformitarianism and catastrophism. In addition, it adds depth to Alvarez’s explanation of how modern geologists acknowledge both gradual and catastrophic forces as important parts of Earth’s history.

“The lunar and planetary evidence for catastrophic impacts was scarcely noticed by a geological community absorbed in the breakthrough of plate tectonics, and all the old uniformitarian prejudices were reinforced by the triumph of the plate tectonic revolution.”

The author explains why the uniformitarian bias dominated the thinking of geologists in the 1960s. While space exploration and the first moon landing posed new questions about asteroid impacts, most geologists did not immerse themselves in space scientists’ discoveries because their interest centered on explaining plate tectonics.

“One dinosaur paleontologist stood alone. Dale Russell, whose Ph.D. was from Berkeley and who worked at the Canadian National Museum of Natural Sciences in Ottawa, had examined the stratigraphic record of the disappearance of dinosaurs in detail and was convinced that it required a sudden extinction. Dale could not imagine a terrestrial event capable of suddenly killing all the dinosaurs, so he suspected an extraterrestrial cause.”

Alvarez credits Dale Russell with being the first paleontologist to assert that some kind of catastrophic event caused the late Cretaceous dinosaur extinction. In discussing how other scientists at the time rejected Russell’s ideas, the book further develops the theme of The Scientific Process of Discovery, showing how scientists’ discoveries often advance incrementally through new theories and debate.

“Radiometric age dates, although not abundant, placed the KT boundary at very roughly 65 million years ago and allowed a gap of no more than a few million years. The enormous faunal change in a short interval of time meant that there had been a mass extinction, and that Lyell’s extreme gradual view was wrong.”

The author explains that the rock evidence from this time period pointed to a sudden change in species, not a gradual die-off. This passage helps convey the role that radiometric dating played in scientists’ ability to date rock layers and understand the sequences of events that occurred as those layers formed. This explanation bolsters the theme of Rocks as Historical Records, since Alvarez and other scientists relied on clues within the rocks to understand the events of the late Cretaceous period.

“The rest of the cliff was made of white chalk, a kind of soft limestone, which was full of fossils of all kinds, representing a healthy sea floor teeming with life. But the clay bed was black, smelled sulfurous, and had no fossils except for fish bones. During the time interval represented by this ‘fish clay,’ the healthy sea bottom had turned into a lifeless, stagnant, oxygen-starved graveyard, where dead fish slowly rotted.”

This descriptive quotation helps convey the scientific thought process of the geologists at Stevns Klint in Denmark, examining the different rock layers and their striking differences. By describing these layers in accessible prose, Alvarez helps illustrate how the catastrophic impact abruptly changed the world’s oceans from a place “teeming with life” to a “graveyard” (71). This intriguing passage adds weight to Alvarez’s impact hypothesis because it confirms that rock layers around the world contain evidence of the same abrupt changes.

“It was a suggestion that sounded reasonable to astronomers, who have photographed supernovas, and to physicists, who understand the nuclear processes that make stars explode. The idea was unpalatable to geologists partly because of the uniformitarian tradition, but partly because no geologist had ever seen evidence for an ancient supernova in the rock record. What kind of rock record would a supernova leave?”

Alvarez describes the interest in—and the skepticism toward—Dale Russell’s theory of a supernova explosion—in the geology community and suggests that other scientists were well placed to comment on such a theory. This quotation reveals how learning about other specializations can help scientists formulate stronger hypotheses and engage in productive debate, adding validity to Alvarez’s belief in the value of interdisciplinary collaboration.

“A young scientist, just starting out, cannot imagine how hard it is to understand the real meaning of Nature’s answers, or how many ways there are to make mistakes and get fooled.”

In this passage, the author humbly admits to being “fooled” by nature’s signs and the evidence embedded in the rock layers. This admission helps develop The Process of Scientific Discovery as a theme, emphasizing that mistakes and failures are a normal part of the scientific process that Alvarez himself experienced many times in his quest to understand the late Cretaceous dinosaur extinction.

“It seemed unlikely that such a big impact site was exposed to view and had remained undetected, so there were three possibilities—(a) the crater was covered over by younger sediments or by the ice on Greenland or Antarctica, (b) it was submerged in the ocean, or (c) it had been destroyed by plate-tectonic subduction of oceanic crust.”

The author summarizes his initial theories about where the impact crater might be located. This discussion shows how his new knowledge led to the more precise questions that directed his research, helping convey how his process as a scientist unraveled the dinosaur extinction mystery. Interestingly, none of these initial guesses was correct; by including these incorrect early guesses, the author again reveals the constant role of failure and persistence in the scientific process, thematically highlighting The Process of Scientific Discovery.

“Throughout the 1980s the KT debate was largely polarized between those who thought the KT extinction was the result of impact, and those who attributed it to massive volcanism. The strengths and weaknesses of the two positions were more or less opposite to each other.”

This explanation centers on the discourse of 1980s geology and acknowledges that scientists had good reason to believe that massive volcanism may have played a role in the dinosaurs’ extinction event. This passage highlights Alvarez’s humble and professional tone as he admits that other geologists also had compelling evidence supporting alternative explanations for the dinosaur die-off. In addition, this quote provides useful context for the author’s later discussion of the continuing mysteries around ancient volcanism and its potential role in different mass extinctions.

“In a good mystery story where the crime is concealed almost perfectly, there is usually a red herring to confuse detectives. In our case the red herring was the misleading evidence, described in the previous chapter, that pointed to an impact in the ocean.”

The author compares his search for the impact crater to a “good mystery story,” making his research intriguing and relatable. He admits his initial mistake of thinking that the impact had occurred in the ocean, when in fact it hit continental crust close to the ocean. By discussing the confusing evidence as a “red herring,” Alvarez continues to compare his research to a mystery novel, portraying himself as a flawed but persistent detective.

“It was a bombshell. The Crater of Doom was found at last! The clue had been the tsunami, generated even though the impact had been on continental crust. Nature had buried the crater and it was completely invisible at the surface, but the tsunami had spread the evidence of nearby impact to an outcrop in Texas.”

This passage presents the answer to Alvarez’s research questions. In naming the impact site the “Crater of Doom,” Alvarez lends a playful tone to his otherwise serious research and conveys the excitement of having definitive proof. This explanation helps explain how tsunami-generated sediment helped geologists trace the impact site’s location and the movements of ocean crust that it generated, enhancing theme of Rocks as Historical Records.

“Some of the cores contained rock which had obviously cooled from a melt, and these first melt-rock samples seemed like the most precious rocks in the world—as rare and informative as the first lunar samples.”

Alvarez again highlights the theme of Rocks as Historical Records by describing the importance of the rock samples that the Mexican oil company PEMEX obtained via deep drilling. By comparing these samples to the first rocks taken from the moon, the author emphasizes the rarity of these samples and their transformative power over scientists’ understanding of the Yucatan impact.

“Over the next few days we studied one KT outcrop after another in superb semidesert exposures—El Mulato where the marker-bed cliff slants up across a muddy hillside, El Penon where you can wander across the exposed top of the KT sandstone bed over an area as big as two or three football fields, Cuauhtemoc where the spherules fill a deep channel gouged into the Cretaceous mud by the tsunami, and Rancho Nuevo where the heavy KT sand has sunk into the soft mud underneath.”

Alvarez refers to the numerous sites in Mexico where he and his colleagues studied, thus illustrating how scientists must confirm their findings as thoroughly as possible so that the scientific community accepts their conclusions as new knowledge. In addition, this passage describes how Alvarez encountered KT boundary rock layers and obtaining samples various locations.

“It is worth pondering the realization that each of us is descended from unknown ancestors who were alive on that day when the fatal rock fell from the sky. They survived, and the dinosaurs did not, and that is the reason we are here now—as individuals and as a species. That one terrible day undid the benefits which 150 million years of natural selection had conferred upon the dinosaurs, making them ever fitter to be the large land animals of Earth.”

This passage encourages consideration of how the Yucatan impact, despite having occurred tens of millions of years ago, has had an effect on each of us because it made our existence possible. This discussion thematically supports The Role of Catastrophes in Earth’s History, prompting reflection on how profoundly different Earth would be had the Yucatan impact never happened.