The Younger Dryas Impact Research Debate – Are We There Yet?
The Younger Dryas impact hypothesis has received considerable attention since its publication in 2007 in the prestigious peer-reviewed journal PNAS (Proceedings of the National Academy of Sciences). It suggests the Younger Dryas geological period and mini Ice-Age, from around 10,850 to 9600 BC, along with associated megafaunal extinctions and human societal changes, was triggered by a catastrophic cosmic impact, probably with a fragmented comet from the Taurid meteor stream. As of now, this paper by Richard Firestone, Allen West and Simon Warwick-Smith and colleagues has amassed over 550 citations in Google Scholar – which is a lot! It is on its way to becoming a classic. But it has also received more than its fair share of criticism, mostly sustained from just a handful of vehement opponents. But has any of their criticism stuck? And what is the status of Firestone et al.’s paper today? Has the dust settled on an outcome? Are we there yet?
Evolution of temperatures in the postglacial period, after the Last Glacial Maximum (LGM), showing very low temperatures for the most part of the Younger Dryas, rapidly rising afterwards to reach the level of the warm Holocene, based on Greenland ice cores. (Evolution of temperature in the Post-Glacial period according to Greenland ice cores.jpg/CC BY-SA 4.0)
One may need a reminder of the importance of this debate. Until quite recently, it was assumed by most academics (but not necessarily by independent researchers) that Earth was protected from large cosmic impacts on the timescale of human development, say the last few 100,000 years, corresponding to the last few Ice Ages. No need to worry about such matters – they are too rare to have any significant effect. Moreover, impacts with comets, specifically, almost never happen, as there are too few comets in near-Earth space to have any significant effect, even on geological timescales.
The Younger Dryas impact hypothesis informs this view of our place in the solar system is wrong on every level. Not only are comet impacts hugely important on geological timescales, they are just as important on the timescale of human development.
The consequences of this concept are profound because it points to reconsidering the understanding of the causes and risks for major changes on Earth, from ancient climate shifts to episodes of extinction. Everything is up for debate on geological timescales.
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Dr Martin Sweatman is a scientist at the University of Edinburgh and a Fellow of the Royal Society of Chemistry. His research, which involves statistical analysis of the motion of atoms and molecules to understand the properties of matter, has helped him to solve one of the greatest puzzles on Earth - the meaning of ancient artworks stretching back over 40,000 years. He is the author of Prehistory Decoded.
Top Image: Ice Age Diorama. From left to right: Equus hemionus, Mammuthus primigenius, Coelodonta antiquitatis, Bison exiguous skeletal mounts at the Tianjin Natural History Museum. (Jonathan Chen/ CC BY-SA 4.0)