page_title: Timeline of Cretaceous–Paleogene extinction event research
section_title: 1980s
hierarchical_section_title: Timeline of Cretaceous–Paleogene extinction event research / 20th century / 1980s
caption_attribution_description: English: Walter Alvarez, professor of geology in the Earth and Planetary science department, presents "Earth History in the Broadest Possible Context." Alvarez recounts revolutions in geology, his work in Egypt, Libya and Tunisia as well as his interests in the Sahara, the Nile and the Mediterranean. Alvarez also tells the tale of the Berkeley Theory, in which dinosaurs were killed by an asteroid impact, developed in collaboration with his father, Nobel Prize winning physicist Luis Alvarez. Alvarez also unveils ChronoZoom, a new tool for the emerging field of "Big History" that makes browsing the past at all scales comprehensible like never before.
context_page_description: Since the 19th century, a significant amount of research has been conducted on the Cretaceous–Paleogene extinction event, the mass extinction that ended the dinosaur-dominated Mesozoic Era and set the stage for the Age of Mammals, or Cenozoic Era. A chronology of this research is presented here.
  Paleontologists have recognized that a significant transition occurred between the Mesozoic and Cenozoic eras at least since the 1820s. Around this time dinosaur fossils were first being described in the scientific literature. Nevertheless, so few dinosaurs were known that the significance of their passing went unrecognized and little scientific effort was exerted toward finding an explanation. As more and more different kinds of dinosaurs were discovered, their extinction and replacement by mammals was recognized as significant but dismissed with little examination as a natural consequence of the mammals' supposed innate superiority. Consequently, paleontologist Michael J. Benton has called the years up to 1920 as the "Nonquestion Phase" of Cretaceous–Paleogene extinction research.
context_section_description: 1980
  Alvarez and others reported spikes in the level of platinum group metals like iridium at the Cretaceous–Tertiary boundary in Italy, Denmark, and New Zealand. They interpreted this sudden introduction of rare-earth metals as evidence for an asteroid impact, to which they attributed the mass extinction at the end of the Cretaceous Period.
  Smit and Hertogen independently reported the presence of an iridium spike at the Cretaceous–Tertiary boundary in Spain, which they also attributed to the impact of an extra terrestrial body and credited with the Cretaceous–Tertiary extinctions.
  May: Smit and Hertogen published the results of their research on the K–T boundary at Caravaca and proposed that an asteroid impact at the end of the Cretaceous triggered the coeval mass extinction.
  June 6th: Alvarez and others published their hypothesis that an impact event cause the extinction of the dinosaurs.
  Penfield wrote to Walter Alvarez, suggesting the Yucatan structure as the possible crater of the end-Cretaceous impactor, but received no response.
  1981
  Orth and others reported a sudden "spike" in the quantity of fossil fern spores near the Cretaceous–Tertiary boundary, "just above the iridium-bearing clay". They also reported an iridium spike at the K–T Boundary in Colorado and Utah. Since these rocks were deposited by freshwater, their discovery bolstered the impact hypothesis by refuting attempts to explain away the K–T boundary's high iridium concentrations as a result of chemical or sedimentary processes occurring in the ocean. This is consistent with the impact event because ferns have been observed to rapidly recolonize areas rendered desolate by modern natural disasters.
  Philip Kerourio debunked Erben and others' suggestion that an increase in the incidence of pathological eggs in dinosaurs led to their extinction. He found that only 0.5–2.5% of eggs in the area Erben and the others studied had multiple shell layers and observed no evidence that these pathologies became more common through the Late Cretaceous.
  A conference dedicated to the end-Cretaceous extinction event was held at Utah's Snowbird ski resort. By this point in time, 36 K–T boundary sites with anomalously high iridium levels had been identified. At the conference, Yale geochemist Karl Turekian disputed the impact hypothesis. He expressed interest in debunking the idea by demonstrating that the isotope ratios of osmium in the rocks of the K–T boundary were typical for rocks of the earth's crust but inconsistent with those in meteorites.
  Wezel and others reported high iridium levels at Gubbio both far above and below the K–T boundary. They also reported spherules likewise above and below the boundary layer and therefore concluded that the spherules could not have been produced by a bolide impact.
  Penfield and Camargo reported the existence a crater dating to the K–T boundary in the Yucatan Peninsula during a presentation to the Society of Exploration Geophysicists. They proposed that this crater may have been caused by the same impact event to which Alvarez had recently attributed the mass extinction at the end of the period.
  Paleontologist Peter Ward reported in a presentation to colleagues at Berkeley that his research supported the idea of a rapid extinction of the ammonites at the Cretaceous–Tertiary boundary.
  Clemons, Archibald and others published one of the first rebuttals to the Alvarez hypothesis. They argued that the fossil record of contemporary plants shows a gradual progressive adaptation of the flora to colder temperatures as the Cretaceous ended and the Tertiary began.
  1982
  Philip Signor and Jere Lipps argued that extinctions can appear more gradual in the fossil record than actually transpired because any given level in the stratum will preserve fewer than the interval overall. They observed a strong correlation between the area of rock deposited during a given time interval and that time interval's biodiversity. This observation is attributable to the obvious fact that the biodiversity of a time interval can only be inferred from fossils preserv
caption: Walter Alvarez in 2012
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