On my shelf is a 2009 book called First Peoples in a New World by archaeologist David J. Meltzer.   I have learned many things from this book, not least of which is that North American archaeology is really, really contentious.  (I may post about this later.) 

On pages 55 – 58, right in the middle of a discussion of the causes of the Younger Dryas, is a long callout box in which Meltzer goes on a delightful rant:

In 2001 the Mammoth Trumpet, a newsletter for a lay audience … carried an unusually long, highly technical article declaring there’d been a Pleistocene doomsday.  A supernova-caused neutron bombardment centered over the Great Lakes had fried the earth 12,500 years ago … heated the atmosphere to over 1,800˚ Fahrenheit, and radiated plants and animals at the equivalent dose of “a 5-megawatt reactor for more than 100 seconds” … and so spiked atmospheric radiocarbon concentrations that ages on Paleoindian sites were thrown off by up to 40,000 years. …  [In 2007] the supposed Pleistocene extraterrestrial catastrophe was hyped as fact from FOX News to The Economist.

Meltzer pp 55 – 56

The Younger Dryas Impact Hypothesis

This claim is now called the Younger Dryas Impact Hypothesis.  The supposed comet impact or impacts are alleged to explain a number of phenomena:

• Just as the last Ice Age was ending, right in the middle of a warming period, the climate unaccountably got cooler again for about 1000 years.  This glacial encore is called the Younger Dryas.  The idea is that a comet impact could have caused a bunch of glacial ice and water suddenly to be dumped into the North Atlantic, cooling temperatures there and interrupting the warming cycle.
• The approximate date for the impact is around the same time that North America’s megafauna (mammoths, giant sloths) were dying out.  Paleontologists are not sure why they died out, because it’s very difficult to get an accurate sense of numbers or of how quickly the extinctions happened.  But if there was a comet impact, that would obviously be the #1 suspect in their demise.
• Also around this time (about 10,800 BC) there is a geologic layer called the Black Mat, a carbon-rich layer that might be burned organic material or might be peat, as from the bottom of a pond.  In some places, it contains nanodiamonds and other unique mineral things that are usually only formed with high heat and pressure.
• This is also the time period in which some archaeologists think the Clovis culture (of humans) was dying out in North America, though this die-off too is controversial.

Impact, Schmimpact

Meltzer, in his 2009 book, is scathing: “The claim was so far out literally and figuratively … it was met with bemusement, or simply ignored.”  He finds all kinds of evidentiary problems with the Younger Dryas Impact Hypothesis.   He doesn’t think an asteroid impact is required to explain the Younger Dryas, for one thing.  (The cooling cycle could have been kicked off by meltwater from the North American glaciers even without a super-hot space rock, since the glaciers were already melting.) Furthermore, Black Mat evidence is inconsistent.  So is Clovis evidence.  So is evidence about the megafauna.  And, the biggest problem of all, in 2009 when his book was published, no one had found an impact crater.

Well, that has changed.  A 31-kilometer-wide impact crater was recently discovered under Hiawatha Glacier in Greenland.  And the proponents of the YDIH have also discovered what they say is additional evidence of impacts as far away as Chile.  (See the links below for more information.)

In Conclusion, We Are Not Sure the World Actually Ended

So, did a huge comet – or multiple pieces of a comet – really hit earth about 12,800 years ago?  Nobody really knows.  But – and this is the only point of this article – how can we not know this? How can we not be sure whether an apocalyptic, species-killing, continent-setting-on-fire event even happened? 

The fact there can be controversy about such a hard-to-miss event just illustrates how difficult it is to figure out anything that happened even a mere 12,000 years ago. Pause for a moment and allow your jaw to drop, as mine did when I first read this, over all … that we don’t … know.

Sources

Fernandez, Sonia. “The Day the World Burned: Geologic and paleontological evidence unearthed in southern Chile supports the theory that a major cosmic impact event occurred approximately 12,800 years ago” posted Friday, March 8, 2019 on UC Santa Barbara, https://www.news.ucsb.edu/2019/019375/day-world-burned

Haynes, C. Vance, Jr.“Younger Dryas ‘black mats’ and the Rancholabrean termination in North America”  Proceedings of the National Academcy of Sciences of the United States of America, published online 2008 April 24, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2373324/

Hurst, K. Kris. “Clovis, Black Mats, and Extra-Terrestrials: Do Black Mats Hold the Key to Younger Dryas Climate Change?” ThoughtCo.com, updated January 15, 2018 https://www.thoughtco.com/clovis-black-mats-and-extra-terrestrials-3977231

Kennett, D.J., et al.. Abstract, “Nanodiamonds in the Younger Dryas Boundary Sediment Layer” in Science 02 Jan 2009, Vol. 323, Iss. 5910, p. 94, https://science.sciencemag.org/content/323/5910/94

Meltzer, David J. First Peoples in a New World: Colonizing Ice Age America, University of California Press, 2009

Voosen, Paul. “Massive crater under Greenland’s ice points to climate-altering impact in the time of humans” posted in Science, Nov. 14, 2018, https://www.sciencemag.org/news/2018/11/massive-crater-under-greenland-s-ice-points-climate-altering-impact-time-humans