This presentation discusses evidence of the extensive fires that were caused by an extraterrestrial impact 12,900 years ago, according to the Younger Dryas Impact Hypothesis.
Transcript:
Younger Dryas smoke and fire controversy. There are currently raging arguments in scientific circles about whether a comet impact 12,900 years ago could have started widespread fires. Opponents of this idea say that forest fires are very common and that there is no proof that the comet impact actually occurred.
In 2006, Richard Firestone and Allen West introduced what became known as the Younger Dryas Impact Hypothesis in a book entitled "The Cycle of Cosmic Catastrophes – How a Stone-Age Comet Changed the Course of World Culture". The book was followed in 2007 by a publication by Firestone and 25 co-authors in the peer-reviewed journal Proceedings of the National Academy of Sciences.
The paper by Firestone proposed that one or more large, low-density extraterrestrial objects exploded over northern North America and that the explosion destabilized the Laurentide Ice Sheet, triggering the Younger Dryas cooling event. The shock wave, thermal pulse, and event-related environmental effects, such as extensive biomass burning and food limitations, contributed to the megafaunal extinctions at the end of the Pleistocene. The paper provided sediment profiles for seven sites which showed increased concentrations at the Younger Dryas Boundary of magnetic grains, microspherules, charcoal, soot, glass-like carbon and carbon spherules.
Images of magnetic microspherules and low-density carbon spherules from various sites in North America were presented as evidence of the extraterrestrial impact, but impact experts were quick to criticize the Younger Dryas Impact Hypothesis. Everything was wrong. The megafaunal extinction and the cooling event could have had other more conventional causes, and all the impact proxies that were presented, like these spherules, were considered insufficient to prove that an extraterrestrial impact had actually occurred. The experts wanted to see an impact crater and evidence like shatter cones and shocked quartz crystals with planar deformation features, which are characteristic of high-speed extraterrestrial impacts.
The Younger Dryas Impact Hypothesis was quickly declared dead by a requiem paper. Charcoal from fires in California was widespread well before and after the time proposed for the extraterrestrial impact, and similar patterns of regional fires were documented across North America and Europe. All the other impact proxies could have been created by ordinary processes. According to the requiem paper, the Younger Dryas Impact Hypothesis had looked at materials from non-catastrophic processes and interpreted them as unique signatures of a catastrophic impact event. For this reason, the impact hypothesis was completely rejected.
Eleven years passed with vigorous arguments from proponents and opponents of the Younger Dryas Impact Hypothesis. In 2018, Wendy Wolbach and several co-authors published two papers about the biomass burning triggered by the proposed Younger Dryas cosmic impact.
The first paper with 26 co-authors claimed that "extensive impact-related biomass burning triggered the abrupt onset of an impact winter, which led, through climatic feedbacks, to the anomalous Younger Dryas climate episode."
The second paper with 30 co-authors said that "the Younger Dryas impact caused extensive atmospheric soot and dust loading that triggered an impact winter. This, in turn, triggered abrupt Younger Dryas cooling and other climate changes, reinforced by climatic feedback mechanisms, including Arctic sea ice expansion, rerouting of North American continental runoff, and subsequent ocean circulation changes."
There is a problem in attributing fires to an extraterrestrial impact. Fires occur everywhere all the time. In 2010, more than 500 forest fires in Russia filled the air with smoke and ignited underground peat-bog fires. The smoke filled many buildings in Moscow, and the Museum on Red Square closed because the smoke detectors kept going off. In 2016, Alberta wildfires constituted the costliest disaster in Canadian History. In July of 2017 wildfires in southern France forced the evacuation of 10,000 people. In 2018, over 8,500 wildfires in California burned an area of about 1.9 million acres.
Wildfires are so common that some plants, called pyrophytes, have evolved to tolerate fire. Giant Sequoias actually depend on fire to reproduce. Fire is an important part of the ecosystem because heat is necessary to open the seed cones, but the trunks of the trees are protected by very thick bark and remain undamaged.
So, how do you distinguish a fire caused by a comet from an ordinary fire? Jennifer Marlon, an expert on biomass burning, has examined sediments in North America dated to between 15,000 and 10,000 years ago. She sees no evidence for continent-wide fires dating specifically to the onset of the Younger Dryas. Marlon says that there is a lot of frustration in the scientific community that the impact hypothesis persists. She, like many opponents of the impact hypothesis, thinks that the comet strike did not happen.
Just because the smoke may have been caused by ordinary fires, we cannot conclude that the extraterrestrial impact did not happen. There is additional evidence. In 2013, Michael Petaev and several coauthors found a platinum anomaly at the Younger Dryas Boundary when examining ice cores from the Greenland Ice Sheet. Platinum is not a common element in the Earth, but it is more common in extraterrestrial material. Christopher Moore reported in 2017 that the platinum anomaly at the Younger Dryas Boundary was widespread in North America and that it could serve as a widely-distributed time marker horizon for identification and correlation of the onset of the climatic episode at 12,800 calendar years before the present.
The Carolina Bays and the Nebraska Rainwater basins may provide the best large-scale evidence of an extraterrestrial impact. The Glacier Ice Impact Hypothesis, published in 2017, proposed that the Carolina Bays and the Nebraska Basins were created by the secondary impacts of glacier ice chunks ejected when a meteorite crashed into the Laurentide Sheet. The impacts of the ejected ice chunks produced seismic vibrations that liquefied unconsolidated ground, and the ice projectiles created inclined conical cavities that were remodeled into shallow elliptical bays by viscous relaxation.
The Nebraska Rainwater Basins have the same elliptical geometry as the Carolina Bays, but they are oriented from the northeast to the southwest, almost perpendicular to the orientation of the Carolina Bays. The Nebraska Rainwater Basins occur on terrain that is 550 to 650 meters above sea level, mainly on sandy soil south of the Platte River. In 2010, Michael Davias determined that the orientations of the Carolina Bays and the Nebraska Rainwater Basins converge at Saginaw Bay, Michigan.
Geologists have tried to explain the Carolina Bays as having been created by wind and water mechanisms, and they have argued that because of the diverse dates, the bays could not have been created by a single impact event. However, the mathematically elliptical geometry of the Carolina Bays is a clue about their origin. Experiments confirm that impacts of ice on a viscous surface produce inclined conical cavities that have an elliptical shape when viewed from above. Impacts have also been shown to produce overlapping bays that cannot be explained or modeled by wind and water mechanisms.
The 2006 book by Firestone and West actually called the Carolina Bays "craters", but when the peer-reviewed paper appeared in 2007, the Carolina Bays had been omitted from the impact hypothesis because they had a wide range of dates not consistent with a single event. LiDAR images have shown that well-preserved Carolina Bays are perfect ellipses and this makes it necessary to conclude that the bays originated as inclined conical impact cavities. The Younger Dryas Impact Hypothesis will gain more acceptance when geologists start to consider seriously that the diverse dates reported for the Carolina Bays are the dates of the terrain, and that these dates do not correspond to the date of bay formation.
