# À propos de la thèse d'un cataclysme planétaire au début des Younger Dryas (12 800 - 11 600 ans) Jérôme R. - novembre 2023 La période géologique dite des *Younger Dryas* correspond à un refroidissement brutal du climat survenu il a 12 800 ans, à la fin de la dernière période glacière, et perdurant pendant 1 200 ans. Sur le plan biologique, cette période correspond à l'extinction de nombreuses espèces de la mégafaune (dont les mammouths). La thèse selon laquelle cette période a été initiée par un ou plusieurs impacts météoritiques cataclysmiques est appelée *Younger Dryas Impact Hypothesis* (YDIH). Elle a été présentée de façon académique en 2007 par Richard Firestone (nuclear analytical chemist at Lawrence Berkeley Laboratory), Allen West et Jim Kennett (earth scientist and oceanographer at the University of California) dans un article intitulé [*Evidence for an extraterrestrial impact 12,900 years ago that contributed to the megafaunal extinctions and the Younger Dryas cooling*](https://pubmed.ncbi.nlm.nih.gov/17901202/). (Proc Natl Acad Sci 2007; 104: 16016–16021), article fondateur de la thèse YDIH (). Un autre article de référence est celui de Michail Petaev (Earth and planetary sciences - Harvard) et ses collègues publiés en 2013 : [Large Pt Anomaly in the Greenland Ice Core Points to a Cataclysm at the Onset of Younger Dryas](https://www.pnas.org/doi/10.1073/pnas.1303924110). Le journaliste d'investigation anglais Graham Hancock a beaucoup contribué à diffuser cette thèse plus largement car elle confirme des hypothèses qu'il avait formulées dès les années 90' au fil de ses recherches sur les civilisations pré-historiques disparues (*Fingersprints of the Gods* - 1996) Dans ses livres *Magicians of the Gods* (2015) puis *America Before* (2019), il expose les principales conclusions des chercheurs sur le sujet et les rapproche et recoupe avec les conclusions d'autres recherches concernant les traces de civilisations antérieures à cette période. Voici un résumé par Graham Hancock lui-même (source : https://grahamhancock.com/america-before/): > >For some decades it has been generally accepted that a global cataclysm occurred around 12,800 years ago at the onset of a mysterious period of earth changes and climate instability known to geologists as the Younger Dryas. Since 2007 a group of more than 60 scientists, publishing in leading peer-reviewed journals, have presented evidence linking the cataclysm to a disintegrating comet that crossed the orbit of the earth 12,800 years ago and bombarded our planet with a ‘swarm’ of fragments, some more than a kilometre in diameter. > >Though compelling, with new corroborative studies published every year, the comet hypothesis remains controversial and a number scientists favour other explanations. What all are agreed on, however, is that a global cataclysm did indeed occur. > >America Before reveals that the epicentre of the cataclysm lay in North America, then still in the grip of the Ice Age with much of the northern half of the continent covered in ice a mile deep. An immense flood was unleashed as large sectors of the ice cap suddenly melted. From the Channelled Scablands of the state of Washington, via the gigantic pot-holes lining the Saint Croix River in Minnesota, to the Finger Lakes of upstate New York, a huge swathe of North America was swept clean by this deluge. At the same time global sea-level rose, the Gulf Stream was stopped in its tracks and the world was plunged into a deep-freeze that lasted 1,200 years. > >It was the end of the former age of the earth, the Pleistocene, and the beginning of our own epoch, the Holocene. In the transition, America Before reveals that an advanced civilization, hitherto the stuff of myth and legend, was lost to history. En cherchant sur le web les articles récents concernant la thèse YDIH, j'ai trouvé celui-ci : [Premature rejection in science: The case of the Younger Dryas Impact Hypothesis](https://journals.sagepub.com/doi/10.1177/00368504211064272) Publié en janvier 2022, il montre d'une part que cette thèse est effectivement un sujet de publications et de débats depuis plusieurs années au sein de la communauté scientifique concernée, d'autre part qu'il semblerait que l'on assiste (une fois encore !) à des rejets hâtifs justifiés par des arguments douteux. Extrait de la conclusion : > It should have been clear to readers, including peer reviewers, that Pinter and Ishman had offered hyperbolic language but no actual evidence against the YDIH; that Surovell et al.37 had failed to sample the YDB and/or made fatal errors in procedure; and that the samples reported by Scott et al.40 and used by Pinter et al.7 and Daulton et al.49 had not come from the YDB and therefore did not bear directly on the impact hypothesis. Instead of critically examining and rejecting these false claims, many geologists and impact specialists embraced them, thereby allowing an alleged absence of evidence to trump abundant, peer-reviewed evidence, even photographic evidence. Then a kind of “groupthink” seems to have set in, rendering the YDIH beneath further consideration.