A fragment of comet, exploded above North America 13 thousand years ago, would have contributed to the disappearance of the megafauna and the collapse of the CLOVIS culture.
In recent years, a group of researchers led by Professor Emeritus James Kennet of the University of California in Santa Barbara has collected new tests that strengthen a very debated hypothesis: that of a fragment of comet that would have exploded above North America about 12,800–13,000 years ago, contributing to the disappearance of the megafauna (such as Mammut and Mastodonti) and the collapse of the CLOVIS (Native American prehistoric culture whose presence in the archaeological sites of North America dates back to about 13,500 years ago).
A step back. To understand how some elements have come to this conclusion. First of all that the recent Dryas (YouTger Dryas) is a sharp return to the cold that interrupts a heating trend at the end of the last ice age, which lasted about a thousand years.
It should then be remembered that Clovis culture, known for its ends of launch characteristics, and much of the North American megafauna disappeared around the beginning of this sudden cold.
Finally, numerous archaeological sites have an often said sedimentary layer “Black mat“(” Black mattress “), rich in carbon, soot, widespread combustion – elements that, according to supporters of the hypothesis, indicate extensive fires and darkening of the sky after the event.
The role of quartz. The most recent discovery – published in the magazine Plos One – which gives strength to the hypothesis of the impact is that of Shocked quartz (Shocked Quartz) found in three classic archaeological sites of Clovis culture: Murray Springs (Arizona), Blackwater Draw (New Mexico), and Arlington Canyon in the Channel Islands, California.
Geologists have discovered quartz grains showing complex fractures (crack) some of which filled with melted silica, characteristics that indicate high temperatures and pressures. Using techniques such as electronic microscopy (TEM, SEM), catholuminescence and EBSD, to analyze the deformations of quartz, deformations that exceed those that could be attributed to volcanism or other ordinary terrestrial activities could have been highlighted. Finally, computer modeling, indicate that an explosion in the air (“airburst“) of a fragmented, low altitude comet could generate the conditions (pressure, heat) necessary to produce this type of shock in quartz grains.
Implications. If confirmed, the hypothesis suggests that the explosion would have caused widespread fires, entry into the atmosphere of smoke, ash and dust, darkening of the sky (“Impact Winter“), reduction of sunlight, and strong environmental stress.
This event combined with other climatic factors may have accelerated the death of the megafauna in North (and perhaps South) America, as well as the decline of the culture of the CLOVIS.
controversial points. The hypothesis is not accepted by the whole scientific community.
In fact, the lack of an evident crater is contested. Normally a great impact leaves geological traces; In the event of recent Dryas this was not clearly identified.
And to explain the events some researchers offer less “catastrophic” explanations, such as changes in oceanic systems, fresh water flows in the Atlantic that may have altered the hot marine currents, or further natural dynamics typical of climate change during glaciation/deglaciations. Some critics then argue that the “proxy” (a physical, chemical or biological indicator that indirectly represents an environmental variable of the past, such as temperature, salinity or concentration of CO₂) used – in this case soot, nanodiancers, microsferule, platinum/iridio – may also derive from terrestrial processes or debris of much smaller impacts, natural combustion or other phenomena still to be identified.
