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 since at least the 1820s that a significant transition occurred between the Mesozoic and Cenozoic eras. Around this time dinosaur fossils were first being described in the scientific literature. Nevertheless, so few dinosaurs were known that the significance of their extinction 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.

Ideas that evolution might proceed along pre-ordained patterns or that evolutionary lineages might age, deteriorate, and die like individual animals became popular starting in the late 19th century, but were superseded by the Neo-Darwinian synthesis. The aftermath of this transition brought renewed interest to the extinction at the end of the Cretaceous. Paleontologists began dabbling in the subject, proposing environmental changes during the Cretaceous like mountain-building, dropping temperatures or volcanic eruptions as explanation for the extinction of the dinosaurs. Nevertheless, much of the research occurring during this period lacked rigor, evidential support or depended on tenuous assumptions. Michael J. Benton called the years between 1920 and 1970 the "Dilettante Phase" of Cretaceous–Paleogene extinction research.

In 1970, paleontologists began studying the Cretaceous–Paleogene extinction in a detailed, rigorous way. Benton considered this to be the beginning of the "Professional Phase" of Cretaceous–Paleogene extinction research. Early in this phase, the pace of the extinctions and the potential role of the Deccan Traps volcanism in India were major subjects of interest. In 1980, father and son duo Luis and Walter Alvarez reported anomalously high levels of the platinum group metal iridium from the K–Pg boundary, but because iridium is rare in Earth's crust they argued that an asteroid impact was needed to account for it. This suggestion set off a bitter controversy. Evidence for an impact continued to mount, like the discovery of shocked quartz at the K–Pg boundary. In 1991, Alan Hildebrand and William Boynton reported the Chicxulub crater in the Yucatan Peninsula of Mexico as a probable impact site. While the controversy continued, the accumulating evidence gradually began to sway the scientific community toward the Alvarez hypothesis. In 2010, an international panel of researchers concluded that impact best explained the extinction event and that Chicxulub was indeed the resulting crater. Because the estimated date of the object's impact and the Cretaceous–Paleogene boundary (K–Pg boundary) coincide, there is now a scientific consensus that this impact was the Cretaceous–Paleogene extinction event which caused the death of most of the planet's non-avian dinosaurs and many other species. The impactor's crater is just over 177 kilometers in diameter, making it the second largest known impact crater on Earth.

19th century

1820s

1825 Georges Cuvier recognized that significant changes to Earth's biota occurred between the Mesozoic and the Cenozoic eras. Because the most familiar and distinctive Mesozoic lifeforms known at the time were marine, he speculated that life had not yet fully conquered the land. He attributed the end-Cretaceous mass extinction to a catastrophic drop in sea levels that destroyed the habitats of the era's characteristic fauna. He concluded that the mammals of the Cenozoic represented Earth's first truly terrestrial fauna.

1830s

1831 Gideon Mantell recognized dinosaurs as evidence for reptilian dominance over the land in addition to the dominion over the sea held by ichthyosaurs and plesiosaurs. He therefore declared the Mesozoic era to be the "Age of Reptiles". Distinguishing the Mesozoic "Age of Reptiles" from the Cenozoic "Age of Mammals" highlighted the differences these two eras of geologic time.

1840s

1842 Sir Richard Owen proposed that the major reptile groups of the Mesozoic were driven extinct as the oxygen contents of Earth's atmosphere rose to levels better suited for birds and mammals.

1850s

1854 Charles Darwin published On the Origin of Species. He regarded the extinction of most taxonomic groups as occurring gradually through the piecemeal loss of member species. However, he considered the extinction of the ammonites at the end of the Mesozoic to have been "wonderfully sudden".

1880s

1882 Othniel Charles Marsh interpreted the extinction of the dinosaurs as a gradual decline over the course of the Cretaceous.

1890s

1898 Arthur Smith Woodward also advocated that the dinosaurs gradually declined into extinction late in the Mesozoic.

20th century

1900s

1905 Frederic Brewster Loomis argued that the plates adorning the backs of stegosaurs were maladaptive traits that sapped their vigor and signaled their impending extinction. Similar arguments would later be extended to the extinction of the dinosaurs overall by Woodward in 1910.

1910s

1910 Woodward gave an address to the British Association for the Advancement of Science in which he declared the cause of the extinction of the dinosaurs to be "racial senility"- the idea that evolutionary lineages had finite lifespans the way individual organisms do and also exhibit age-related deterioration over time as well. Woodward argued that traits like large size, spiny coverings and lack of teeth seen in some later dinosaurs were signs that the group was approaching its inevitable end.

1917 Franz Nopcsa suggested that dinosaurs may have developed overactive pituitary glands that led them to become pathologically gigantic in an evolutionary parallel to acromegaly in modern humans. He also suggested that a "[d]iminution of sexual activity" may have played a role in their demise.

1920s

1921 William Diller Matthew argued that dinosaurs were gradually driven extinct as geologic uplift replaced the wet lowland habitats Matthew thought dinosaurs were best adapted to with the more elevated terrain he thought was preferred by mammals.

1922 Nopcsa proposed a model for the extinction of the dinosaurs similar to Matthew's but with greater emphasis on the implications the uplifted terrain had for the plants they depended on. He also suggested that competition from mammals that arrived in North America from Asia played a role. N. M. Jakolev proposed that the dinosaur went extinct because Earth's climate became too cold to sustain them.

1923 Roy Lee Moodie proposed that dinosaurs were killed off by diseases. Examples of the pathological health conditions Moodie thought contributed to the extinction of the dinosaurs included arthritis, dental cavities, fractures, and infections.

1925 Paleobotanist George Wieland hypothesized that Tyrannosaurus rex survived on a diet of eggs. He argued that feeding its great bulk would have led it to consume the entire last generation of dinosaurs before they could even hatch, leading to their extinction. He also suggested that mammals may have driven the dinosaurs extinct by eating all of their eggs.

1928 L. Müller proposed that volcanic eruptions drove the dinosaurs extinct. H. T. Marshall suggested that bombardment from cosmic or ultraviolet radiation caused the extinction of the dinosaurs.

1929 Alexander Audova analyzed the circumstances of the extinction of the dinosaurs and concluded that they were driven extinct gradually when Earth's climate cooled too severely for their embryos to fully develop in the egg. He dismissed the idea that they went extinct due to factors like racial senility.

1930s

1939 Percy Raymond suggested that dinosaur brain size diminished over the course of the Mesozoic until, in effect, they became too stupid to live and went extinct. William E. Swinton argued that dinosaurs were driven extinct when the lakes and swamps they inhabited dried up.

1940s

1942 Wieland suggested that the dinosaurs were driven extinct when the amount of carbon dioxide in Earth's atmosphere decreased until it was too low to instigate them to breathe and they suffocated.

1945 Raymond B. Cowles proposed that the dinosaurs went extinct when Earth's climate became so hot and dry that it affected the ability of male dinosaurs to produce sperm cells.

1946 Edwin Harris Colbert and others proposed that the dinosaurs went extinct when Earth's climate became too hot and dry to support them.

1949 Cowles proposed that in addition to preventing dinosaurs from producing sperm, elevating temperatures and aridity at the end of the Mesozoic would have killed vulnerable young dinosaurs, another factor that could have contributed to their extinction. Martin Wilfarth argued that dinosaurs were marine animals and were driven extinct by decreasing sea levels during the Late Cretaceous, which dried out their habitats.

1950s

Petroleos Mexicanos, also known as PEMEX, discovered an unusual subsurface circular structure in the Yucatan Peninsula of Mexico.

1954 E. Stechow proposed that the extinction of the dinosaurs may be attributable to solar flares that destroyed the ozone layer, allowing ultraviolet radiation to shower the planet.

1956 Max Walker de Laubenfels hypothesized that at the end of the Cretaceous, a bolide entered Earth's atmosphere, "[f]lash heating" it and incinerating the dinosaurs.

1960s

PEMEX began drilling into the unusual ring-like structure under the Yucatan and extracting rock cores in search of oil.

1962 Stanley E. Flanders suggested that at the end of the Cretaceous caterpillars began multiplying until they had so denuded the contemporary plant life that nothing was left for the dinosaurs, who starved to death.

1967 John M. Cys argued that dinosaurs went extinct because they were unable to hibernate during the winter, leaving them doomed by Earth's changing climate.

1968 Daniel I. Axelrod and Harry Paul Bailey proposed that the dinosaurs were driven extinct when Earth's climate began exhibiting more marked seasons rather than stable conditions year-round. Helen Tappan suggested that the dinosaurs were driven extinct as Earth's terrestrial environments began to flatten out, eliminating their preferred habitats. K. D. Terry and Wallace H. Tucker suggested that the dinosaurs may have been driven extinct by ionizing radiation.

1970s

PEMEX continued looking for oil deposits associated with a large circular structure in the Yucatan Peninsula.

1970 C. B. Hatfield and M. J. Camp suggested that the dinosaurs went extinct due to Earth's "[o]scillations about the galactic plane".

1971 Dale Russell and Tucker proposed that a nearby supernova emitted a burst of electromagnetic radiations and cosmic rays that killed off the dinosaurs.

1972 Peter Vogt reported evidence of intense volcanic activity occurring in India around the end of the Cretaceous. He hypothesized that this volcanic activity released poisonous trace elements which brought about the mass extinction.

1973 Harold Urey argued that comet impacts may have caused mass extinctions in the past and may have been responsible for demarcating the periods of the geologic time scale.

1974 Jan Smit began studying the extinction of foraminifera at the K–T boundary in Caravaca, Spain. He observed that some of these extinctions must have been rapid.

1976