The first proposal that a comet struck North America at the end of the last ice age was introduced in the 19th century by the populist politician and conspiracist
Ignatius Donnelly as an alternative hypothesis to glaciation. In his 1883 book
Ragnarok, he posited that such an impact explained clay and gravel deposits spread across North America as a result of the cometic collision and that it had wiped out the fictional lost civilization of
Atlantis. YDIH is a
fringe hypothesis purported to explain the cause of the sudden cooling at the end of the
Last Glacial Period, the
Younger Dryas (YD) period. It was formally introduced in 2007 by nuclear physicist Richard Firestone and collaborators in the
Proceedings of the National Academy of Sciences of the United States of America Firestone and collaborators elaborated on the hypothesis substantially in their 2006 book
The Cycle of Cosmic Catastrophes, though one of its co-authors denies the book was meant to be scientific. However,
genetic evidence indicates that the Clovis people migrated southward and adapted to the changes in their environment. Anthropologist
Vance T. Holliday has also argued that evidence shows that there is no requisite break in the archeological record, but instead that the Clovis people did not stay in one site for very long and that
Folsom points appear in the record simultaneously with the disappearance of megafauna hunting tools. The widely accepted cause of the freshwater influx is meltwater from retreating ice sheets In 2011, Pinter and collaborators set out to review and test YDIH and to present the results of such tests. They concluded that the hypothesis was rejected on the basis that the results of the 2007 study could not be
reproduced and were instead a misinterpretation of data, This remained the "last hope" for the hypothesis, despite the lack of an impact crater, until a study led by physicist Tyrone Daulton concluded no such nanodiamonds could be found. Another study by
geophysicist Jay Melosh showed that an air burst from such an impact could not produce the amount of pressure necessary to form nanodiamonds. Instead, a 2010 study led by paleobotanist Andrew C. Scott found fossil evidence that the materials found were fungi or
insect fecal pellets. Additional studies in 2016 replicated the refutation of the existence of the nanodiamond evidence. and the 2015 discovery of the
Hiawatha impact structure. However, in 2018 Melosh argued that it was statistically unlikely the impact was recent given that an object the size of the projectile would only collide with Earth once every few million years. He also said that it was too small to cause a catastrophic extinction event in the continental United States. A 2025 study led by
volcanologist Charlotte E. Green found that the elevated platinum occurred 45 years after the onset of YD, and thus too late to support YDIH, and lasted for 14 years, which negated an instantaneous cataclysmic event. Green and her co-authors concluded instead that the platinum spike was due to sustained
fissure eruptions in Iceland, which was consistent with several other previous studies. Other evidence cited in support of YDIH includes black mats, or
strata of organic-rich
soil (which contained the purported nanodiamonds), Both Marlon and Pigati argued that various natural processes unrelated to an impact could explain their presence. Likewise, Pinter and collaborators later found that the magnetic spherules were instead consistent with iron-rich
detrital grains of anthropogenic or otherwise terrestrial origin. Afterward, several co-authors of the paper distanced themselves from YDIH. Philanthropist and early Googler Eugene Jhong donated $1.25 million across two universities to fund CRG's work. The group publishes research about real geological phenomenons with alternative explanations that diverge from scientific consensus. Since its forming, CRG has grown in collaborators and, since 2021, published several papers it claimed confirmed the validity of YDIH, arguing it was no longer a hypothesis, but instead a
scientific theory, including a 2021 paper authored by theoretical physicist Martin Sweatman, who rejected all rebuttals of his work as "poorly constructed."
Tell el-Hammam and data manipulation In September 2021, CRG collaborators published a hypothesis about an ancient city destroyed by an air burst from a meteorite at the archaeological site
Tell el-Hammam 3,600 years ago. The study was led by a biblical archaeologist purported to be the site of the ruins of
Sodom, a Biblical city destroyed in the
Book of Genesis by God for
wickedness. CRG members initially denied tampering with the photos but eventually published a correction in which they admitted to inappropriate image manipulation. Five of the paper's 53 images received retouching to remove labels and arrows present in other published versions of the photos, which Bik believed to be a possible conflict with
Scientific Reports' image submission guidelines but was not in itself a disproval of the Tall el-Hammam air burst hypothesis. On February 15, 2023, the following editor's note was posted on this paper: "Readers are alerted that concerns raised about the data presented and the conclusions of this article are being considered by the Editors. A further editorial response will follow the resolution of these issues." On April 24, 2025,
Scientific Reports issued a
Retraction Note, citing concerns about methodology, analysis, and data interpretation. Another unrelated paper authored by a CRG member and leading YDIH advocate was retracted by
Scientific Reports in 2023. The journal's Retraction Note cited a publication "indicating that the study does not provide data to support the claims of an airburst event or that such an event led to the decline of the Hopewell culture." == Public interest ==