Alvarez and the Story of Dinosaur Extinction

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Apr 3, 2024

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Name Umar Fazil Asteroids and Dinosaurs: Unexpected Twists and an Unfinished Story Let us use the story of Water Alvarez and his investigation of what happened to the dinosaurs as a model for How Science Works. This story can be found on our course website or at http://undsci.berkeley.edu/lessons/pdfs/alvarez_wflow.pdf . We will focus on the role of communication and collaboration in the process of science, which is the lavender circle on the “How Science Works” flowchart found below.

Name Umar Fazil 1. From Plate Tectonics to Paleontology What was Walter’s “surprising observation” and what “question did he ask” as a result of this observation? Walter Alvarez's team discovered an unusually high concentration of iridium in a layer of clay from the K-T boundary. The iridium levels were over 30 times higher than expected. This led to the term "iridium anomaly" to describe the finding. Alvarez wondered if this anomaly indicated a local event or a global disaster. This question opened up further investigation into the causes of the mass extinction at the K-T boundary .

Name Umar Fazil 2. False Starts and a New Lead After discussing ideas with his father, Luiz Alvarez (a physicist), what was the hypothesis that Walter came up with? What were his expected results? After discussing with his father, Luis Alvarez, Walter came up with the asteroid impact hypothesis. This idea would account for the high levels of iridium and the absence of plutonium. They expected that a huge asteroid striking Earth would have thrown enormous amounts of dust into the atmosphere. This dust cloud would have blocked sunlight globally, halting photosynthesis and plant growth, leading to the collapse of food webs and a mass extinction event. These expectations fit with the observed evidence: no plutonium, high iridium levels, and a major extinction event.

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Name Umar Fazil 3. The Plot Thickens …

Name Umar Fazil What were actual results from Walter’s iridium experiment? How did his team interpret this data (was it supportive, contradictory, surprising, inconclusive)? Did this data support their original hypothesis or did it inspire a revision to their assumptions? What action did they take as a result of this first iridium experiment? Walter Alvarez's iridium experiment revealed a surprising and clear result: the K-T boundary clay contained iridium levels over 30 times greater than expected. This discovery, termed the "iridium anomaly," suggested something extraordinary had occurred to cause such a spike. Subsequent tests showed that the anomaly was a global event, further supporting the asteroid impact hypothesis. Follow-up measurements even found iridium concentrations as high as 10 parts per billion. The data corroborated the team's original asteroid impact hypothesis without necessitating any revisions. Inspired by these findings, Alvarez and his team proceeded to investigate the iridium levels' global distribution and implications. 4. Another False Start

Name Umar Fazil What was Alvarez’s new hypothesis? What were the expected results? Did the experiments ultimately support or oppose the hypothesis? In the figure above, why does the orange arrow do a “loop-d-loop” twice through the Gathering data/Interpreting data circle? Alvarez's new hypothesis, after discussions with his father Luis and other colleagues, was that a massive asteroid had struck Earth at the end of the Cretaceous period. This impact would have thrown millions of tons of dust into the atmosphere, which would have blocked sunlight globally, stopped photosynthesis, and consequently led to a collapse of food webs. The expected results of this hypothesis were a global catastrophe leading to mass extinctions, which matched the geological and paleontological evidence. The experiments and further evidence gathered did support this hypothesis, indicating that it was a global event, not a local or

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Name Umar Fazil isolated one. The “loop-d-loop” in the orange arrow in the figure likely represents the iterative process of scientific inquiry, where gathering data and interpreting it leads to new hypotheses and further rounds of data collection and analysis, a cycle that is repeated as the scientific understanding deepens and evolves . 5. Three Observations, One Hypothesis What is the new hypothesis of Alvarez’s team? What were the expected results? Did this match the actual results?

Name Umar Fazil Alvarez's team formulated a new hypothesis that a massive asteroid impact caused the mass extinction at the end of the Cretaceous period. They expected this event would be evidenced by high levels of iridium, lack of plutonium, and a record of mass extinction. The hypothesis was that the asteroid impact threw up a dust cloud that blocked sunlight, disrupting photosynthesis and collapsing food webs. This matched with the actual results they found: high iridium levels and a corresponding layer marking a mass extinction in the geological record. The hypothesis accounted for the distinct lines of evidence and was supported by their findings. These results led them to further investigate how such an event could have led to the extensive mass extinction observed in the fossil record . 6. A Storm Front In 1980, Alvarez and his team published their hypothesis linking the iridium anomaly and the dinosaur extinction in an article in the journal Science . How does what happened after the

Name Umar Fazil publication of their article exemplify the community analysis and feedback section of the “How Science Works” flowchart? After Alvarez and his team published their hypothesis in 1980, it set off extensive scientific debate and research. Scientists worldwide began to replicate their findings, confirming that the iridium spike at the K-T boundary was a global phenomenon. This validation led to a surge in interdisciplinary research, with over 2000 scientific papers published on the topic within the next decade. Experts in paleontology, geology, chemistry, astronomy, and physics all contributed new evidence and theories, exemplifying the community analysis and feedback stage of the "How Science Works" flowchart. This stage is characterized by peer review, replication of results, and theory building, which were all vibrant parts of the scientific response to Alvarez's publication . 7. The Eye of the Storm

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Name Umar Fazil Describe 2 other lines of evidence that were explored by the scientific community that were relevant to Alvarez’s asteroid hypothesis. Did this evidence support or oppose the asteroid hypothesis? Two other lines of evidence explored by the scientific community that were relevant to Alvarez's asteroid hypothesis included tsunami debris and the discovery of a crater: 1. Tsunami debris: The hypothesis suggested that if a large asteroid had struck one of Earth's oceans, it would have caused massive tsunamis. These tsunamis would have moved sediments from the ocean floor and deposited them in different locations. This would mean that at the K-T boundary, scientists would expect to find debris beds from tsunamis. 2. Crater: The hypothesis also predicted that the asteroid impact would leave behind a significant crater. This crater, assuming it hadn't been destroyed by tectonic activity, should be dateable to the end of the Cretaceous period. The evidence supported the asteroid hypothesis: the K-T boundary is marked by impact debris such as bits of glass, shocked quartz, tsunami debris, and indeed, the Chicxulub crater off the

Name Umar Fazil Yucatan Peninsula was identified as the site of a massive asteroid impact. This discovery, initially made during oil exploration, was later connected to the asteroid hypothesis in 1991, providing substantial support for Alvarez's theory. 8. It’s Not Over ‘Til …

Name Umar Fazil With so much evidence supporting the asteroid hypothesis, is this the end of the story? Do we KNOW what happened to the dinosaurs with 100% certainty? Why or why not? Even with the substantial evidence supporting the asteroid hypothesis, it's not the absolute end of the story regarding the extinction of the dinosaurs. In science, few things are ever known with 100% certainty, as new evidence could emerge that refines or even contradicts current understanding. The asteroid impact is widely accepted as a primary cause of the mass extinction at the end of the Cretaceous period, but scientists continue to study the event to understand the full complexity of the extinction. For example, there are studies on the role of volcanic activity, climate change, and other environmental stressors that may have also

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Name Umar Fazil contributed to the extinction. Additionally, the fossil record is incomplete, and new discoveries can provide further insights into how exactly the dinosaurs died out. Therefore, while the asteroid impact hypothesis is strongly supported, the scientific community remains open to new information that could expand or adjust this narrative.

Alvarez and the Story of Dinosaur Extinction

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