... and even more on the YD boundary event debate

3 Oct 2010

The next day, October 2nd, George Howard posted the Holliday and Meltzer paper at http://cosmictusk.com fully and completely, including an extensive discussion in which a whole raft of other scientists commented on the issue - in what I think is a quite splendid scoop by George and highly commendable. It can be dowloaded in pdf format but consists of a lot of pages of print-out. It is nevertheless a valuable asset to anyone even remotely interested in catastrophism and if, like me, reading online at the computer screen is not comfortable, then a print-out is to be commended - especially as it can be kept for future reference.

The paper begins by acknowledging the Firestone et al paper (2007) and Kennet et al (2009) and the book, The Cycle of Cosmic Catastrophes and lays out the basic theory of the YD boundary event hypothesis before proceeding to criticise aspects of it - but not the theory in its entirety. It is important to understand at this juncture that the Younger Dryas event is not a peculiarity - and this is what Holliday and Meltzer are aware of as they write. Indeed, the Younger Dryas is very similar to a series of events now known as Heinrich events - and these litter the Late Pleistocene era (or pop up regularly during the last 100,000 years). Although it has not been spelled out as far as I know the implication is that most of the events could theoretically be embraced within the Clube and Napier model - only by assuming the progenitor comet was active over such a long time. If this was so one might theorise that earth periodically encountered large streams of dust and debris discharged from the surface of the comet and this was the main reason for the succession of cold periods (Heinrich/ Dryas events). Hence, it is not necessary to visualise an actual impact event at the beginning of the YD event - but is not of course excluded. Opaque atmospheric conditions may have ensued for long periods of time - but once again there is a problem as these events lasted for especially long periods of time, too long for a passage through a dense stream of meteoroids and comet debris. It does have the benefit of explaining, perhaps, the rapid nature of the warming at the end of the Younger Dryas event, assuming it was caused by the orbit of the earth emerging out of such a stream of material (or the upper atmosphere being washed of dust and debris by an oceanic impact, perhaps). The YD boundary event theory does not address any of the Heinrich events - or the nature of the rapid warming that took place at the end of the Younger Dryas. The consensus model explains these things by the ocean current conveyor belt system and atmospheric changes resulting from that - but it is an equally little understood process that some people think they know how it may work but others go along with it as there is no other explanation adequate to explain what happened. Hence, there is a niche that the Clube and Napier model could fill - but only if archaeologists and geologists and other scientists explore the right things rather than ignore what Firestone et al think is important information. This was the nub of the exchange on October 1st.

Hence, when the paper begins by assuming the Firestone et al hypothesis requires a crater that does not appear to exist - they may be arguing from the wrong perspective. However, this is not the way Holliday and Meltzer approach the problem - they proceed by arguing solely from the archaeology (or the lack of evidence either way). For example, differences in Clovis and post-Clovis human societies are poorly understood - there are surprisingly very few sites. Goodyear, in (1999) argued that large mammals such as mammoth played only a small role in Clovis diet as they were already on the point of extinction. On the Great Plains bison became an important prey species - but they are just one of several favoured prey species. In fact, it has been argued Clovis diet was primarily based around bison, just as it was in post-Clovis times. This is important as the actual Ice Age had come to an end several thousand years before the Clovis era. These people occupy a niche separated by the cold Ice Age and a cold interlude, the Younger Dryas - in which winter temperatures seriously declined. In all likelihood, the people who lived in that period between the Ice Age and the YD in Britain were the same people that lived there after the YD event - so there is no reason to suppose that did not happen in North America too. Essentially, that is the argument made against the YD boundary impact event. Most large mammals had died out before Clovis and species like mammoth survived only in small numbers. The Clovis people were quite capable of surviving a cold interlude such as the YD event - if that is all that it was.

Holliday and Meltzer set up a good argument. The downside is the likelihood of a C14 plateau event which muddies their evidence - which is based on C14 dating methodology. Likewise, the geology could theoretically be interpreted in a different manner too - by geomorphic processes and as time-progressive. This depends on how literally one takes the uniformitarian principles. In this instance, the black mat and related layers may date from 18,000 to 9,000 BP as suggested by Holliday and Meltzer or the whole range from the end of the Ice Age to the end of the Pleistocene (= end of YD event). This might imply a catastrophic admixture of the sediments over a period that represents a really very small measure of time on the geological clock. In addition, if major geological deposits are primarily laid down in catastrophic circumstances this means the longer phases of geological history are actually absent from the record preserved in rocks. This does not apply to such things as lake and bog sediment cores but even these must have been affected to a degree by catastrophic events. Geology is a complex issue but it is not inconceivable that if there had been an impact per Firestone et al and then sediments could have been laid down rapidly - in some circumstances, at least. Hence, the supposed gap or sterile phase used by Firestone et al as proof of population collapse may be an idea seriously at odds with reality.

As this is the third post on this particular paper it is unneccessary to go through it tooth and nail. However, on pages 584-597 (of the journal) we have a 'Discussion' in which a variety of other scientists have been invited to comment. This is actually one of the most illuminating aspects of the print-out and by far the bigger part of it (in totality around 30 pages in all). Considerable argumentation is made on the dating problems concerning the C14 methodology and an apparent plateau - which is to be expected as it represents the weakest part of the arguments made by Holliday and Meltzer. Cultural differences, or lack of them are also addressed.

Louis Alberto Borrero makes an interesting point by suggesting the YD was a trigger for humans to migrate in large numbers to South America (where he has done most of his research) but he adds, there is currently no evidence of a decrease in population in North America, and anyhow, humans were probably well established in South America long before the Younger Dryas. He also points out another anomaly scarcely noted by others, the extinction of large mammals was not confined to North America - they also disappeared from South America.

Marie Agnes Courty, who addressed one of the SIS Cambridge Conferences in the 1990s, concerning the Bronze Age Destructions, offered a different way forward that I'm sure would please Rick Firestone. If archaeologists and geologists in the future actually looked for minerological markers from various high resolution records of the last glaciation and made this a research priority the answer to the YD boundary event hypothesis would eventually emerge - one way or the other. Considering the global dimensions of the YD event exploration beyond North America was long overdue. She is critical of the fact that impact volatiles are not looked for during excavations and geological sampling - anywhere. this even holds true of a known impact event, that of Tunguska. It was never properly investigated and the likelihood there have been repeated Tunguska like episodes in the past, even in the Holocene, , makes it imperative that proper research of geological layering is done.

An Australian scientist, Judith Field, made the point that Australian megafauna became extinct by 30,000 years ago - or mostly so. It may actually have lingered on in small numbers, is the inference, which is an interesting observation - just as mammoths survived into the Holocene on Wrangel Island. She is obviously critical of the overkill hypothesis - which has soiled the Clovis debate by concentrating on a few Clovis points found in mammoth skeletal material. Although this coincidence has never yet been found in Australia it has not stopped academics and various commentators (such as politicians and environmentalists) from blaming the Aborigines for their disappearance. She also makes an interesting point on top of this - in Australia fossil fauna of large animals is only accepted if they contain articulated skeletal material allowing geochronologists and ecologists to stitch the Aborigines up by placing the extinctions within the window of 40 to 50 thousand years BP. If the same criterion was applied to the North American fossil record we might well be looking at an extinction process that actually preceded the arrival of humans by thousands of years - and that really would open the debate.

ME Hill, an anthropologist began by saying he disliked the idea of impact catastrophism - and expressed the hope the discussion would develop along other routes. BB Hucknell of the University of New Mexico accepts the population crash in eastern North America is illusory. Douglas Kennet, on the other hand, is adamant that new archaeological research is what will test the hypothesis. He suspects that when strict criteria for accepting or refuting C14 dates are applied to Holliday and Meltzer's data set even fewer sites will be seen to have existed during the YD period - and that will amplify the gap in occupation (if there are any). Marcel Kornfeld on the other hand suggests that bison were the major prey animal of Clovis people - not mammoths. The emphasis on the latter is relevant to the overkill theory, not to the facts on the ground. However, he also accuses the YD impact team of cherry picking 'factoids' to demonstrate their hypothesis, and when they trespass into foreign territory such as archaeology, it is easy to misinterpret the data. He sees the Holliday and Meltzer paper as correcting the ill founded elements within the YD impact event hypothesis.

Marlon and Bartlein began by saying the YD impact is 'an extraordinary claim' - obviously, they have isolated themselves from earlier catastrophist literature. In spite of this they go on to point out the origin of black mat layers requires some kind of explanation - what did actually happen, as well as questions we might ask about abrupt environmental changes that did occur between glacial and interglacial conditions in the Late Pleistocene. It involved abrupt shifts in climate, rapid migrations of human populations, and megafauna extinctions as well as a massive reorganisation of vegetation and associated eco-systems. What was going on? The  multiiple changes in conditions is evidenced by hundreds of palaeo-environmental records that track those changes in vegetation - and in fire regimes. Vegetation changes in NE America were especially rapid and more widespread at the beginning and at the end of the YD event.

James Steele of University College in London says the impact debate has stimulated renewed research on the general issue of demographic dispersal at and during the YD event, and he goes on to highlight problems with C14 dating, as well as a statistical analysis of Holliday and Meltzer's particular sample of C14 dates. He comes up with some interesting points most people outside the area of study are not aware of and that is that a Huon Pine tree ring (HP 40) sequence has anchored the Late Glacial Pine sequence (LGP) and actually supports a reduction in calendar years of C14 determination between 12,900 and 12,550 BP. Further revisions of the calibration curve are in the offing - which is good news.

TA Surovell, University of Wyoming, began by saying the Holliday and Meltzer paper produces evidence that is so obvious it is virtually unneccessary to express - but continues this rebuff of the YD impact theory by saying the Firestone et al model should not be allowed to go uncontested (and he is the co-author of one of the papers that muddied the waters). He adds, he has doubts that the fiction of an impact can be resolved in the archaeological record - it requires testing by geologists. He predicts the hypothesis will be like a meteor at night - a bright flash of ligt but then disappearing as quickly as it appeared. A bit of wishful thinking perhaps - or an observation made by a superiority complex.

Lastly, MR Waters returns to the C14 dating problems and suggested that what was needed was a series of new unfettered C14 dates in order to test the theory fully.

Altogether, an excellent read.