Rod Chilton, author of the most recent (and perhaps only) comprehensive review of Younger Dryas science, was kind to contribute this fine critique of David Morrison's recent paper in Skeptical Enquirer. I am reading Rod's excellent book and look forward to reviewing it soon.
The debate continues as to the cause of the more than 1,000 year-long cold interval known as the Younger Dryas. Falling on the heels of the Last Ice Age, or more correctly immediately after the two warm intervals known as the Bolling and Allerod interstadials, the Younger Dryas onset appears now to have started in as little time as one to three years. The climate shifted that suddenly from near present day warmth to near Ice Age cold. A second important feature to be noted is that apparently most of the planet was affected, and that the teleconnection between various parts of the planet was swift. This suggests strongly that the forcing mechanism resided in the atmosphere, rather than in the Ocean (where a much slower teleconnection would have been evident). The Younger Dryas however was very different from another alleged cosmic encounter, that of the great Cretaceous extinction event of approximately 65 million years ago. At this time, a huge bolide struck the Gulf of Mexico. Likely measuring as much as ten kilometres' across, the demise of the dinosaurs seems to have been assured.
However, the Younger Dryas cosmic event is envisioned as considerably different, that is if astronomers William Napier and Victor Clube are correct in their calculations. Drs, Napier and Clube believe that what is a far more likely type of encounter is best described as a "cosmic shower." The nature of such an event would have a cosmic stream of already broken up comet and asteroid pieces striking earth, but extended over widespread areas as the influx took place more as showers than as single objects. All manner of sizes from very small through Tunguska-sized and finally on upwards to objects possibly one half kilometre wide or more pummelling planet earth. Thus the proof of such an encounter will despite being from a much less distant time, will nonetheless be somewhat more difficult to discern than was the case for the K/T dinosaur event.

That said, only if scientists remain open minded will the clues that are out there reveal the true nature of the Younger Dryas cosmic encounter. So it is then that the evidence continues to accumulate despite considerable scepticism on many fronts. Apart from what was a very sudden onset, in as little time as one to three years. And too, the nature of the event in affecting all of the Northern Hemisphere and a good part of the south is revealing in itself. This because of the rapid teleconnection to most all parts of the planet all at once. I wish to stress here that the detection of nanodiamonds and magnetic microspheruels in what is an enigmatic layer throughout North America and Europe is but one part of the story. Considerable weight to this part of the evidence has now come to light in another part of the world by different researchers (this in Venezuela). Criticism of some of the results of the group of twenty plus scientists has been forthcoming from some quarters such as Dr. Todd Surovell. Dr. Surovell was unable to replicate the finding of increased nanodiamonds for instance in his work in North America for the sedimentary layer dated at 13,000 BP. However, a retort from Dr. Richard Firestone, one of the main investigators within the group of twenty plus scientists pointed out that the layer Dr. Surovell was testing a much wider and therefore less concentrated sample of any anomalous materials such as nanodiamonds.

The work of the scientists in North America has not been the only research that has revealed some enigmatic features round about the time of the Younger Dryas. A related but somewhat different means of detection. Dr. Lars Franzen of the University of Goteborg in Sweden has also collected some very good evidence of at least a cosmic presence in some form, extending all the way back from approximately 8,000 BP to the Younger Dryas 13,000 years ago. Dr. Franzen's indices are based upon detection of rare on earth elements collected from a number of peat bogs from various localities around the planet, including China, South America, Ireland and Sweden. Also as important in the ongoing debate must be the greatly elevated and difficult to account for peaks of ammonium and nitrates primarily found in the high resolution Greenland Ice Cores. The explanation that holds the most validity for the ammonium spikes is that of wildfires that appear to have affected large areas of North America at the time of the Younger Dryas. Wildfires that were I believe started by cosmic objects either air bursting over the landscape and/or actually striking vegetated portions of North America. Another possilbe sorce for ammonium is an interesting idea as presented by Dr. Adrian Melott; this is known as the Haber process, which literally cooks the atmosphere and produces ammonia in this fashion. Nitrates for their part can be seen as being a by-product of incoming bolides heating the atmosphere to ozone destroying levels; the nitrates then accumulate as well within localities such as the Greenland Ice Sheet. Then there are increases in elements such as potassium 40 and Helium 3, both rare on earth but much less so in space. Looking to concurrent increases in two radionuclide's ( a possible sign as well of cosmic activity) their marked increase is difficult to reconcile by any other means than a very large cosmic encounter.

The investigation should not end here! There are in addition a whole gamut of other important features that validate the Younger Dryas as caused by a cosmic encounter. These factors have largely been left out of the discussion to date. They are however, when considered in context with all the other evidence just as important to the ongoing debate. A brief list should include at least some of these important components:

1) Attention should be paid to the astronomical evidence in all its forms. So not just the deposition of comet remnants, but other important features that can be deduced from such items like the zodiacal light (just recently gaining support as caused by cometary influences). Also, a look to our moon has already shown some interesting evidence of increased comet visitation in the time frame 10,000 to 20,000 BP. Also, by predicting where the orbits and positions of potential candidates for comet impact here on earth as is the case with the Taurid meteor stream is of ongoing importance.

2) A look to not just the continents, but to the oceans as well is something that may be beginning to take place. As over 75% of the globe is covered by oceans, any evidence found here would be extremely valuable. Dr. Sharma presented some preliminary findings at the AGU conference last autumn in San Francisco. Here it was reported that there are indications of a cosmic event, possibly from the Younger Dryas time. Dr. Sharma is in the process of writing a paper on these results.

3) Somewhat related to this development I believe are the extremely enigmatic deposits of animal and forest remains that remain unexplained throughout parts of Alaska and Siberia. The distinct possibility exists that meteorites striking the Pacific Ocean created what can only be called "megatsunamis." If so, the destruction of large number of ice age animals may well be seen as plausible by these means. In addition, all manner of other features that may well have taken place, such as the extremely rapid onset of cold, the destruction of much of the planet's protective ozone layer, likely acid rain, destruction of much of the vegetation in large areas all like contributed to the ice age mammals demise. That the die-offs were extreme, especially in the Americas where as many as 73% of the species disappeared in North America, and even greater numbers (80%) than that in South America may well be reconciled by a cataclysm of the magnitude suggested here.

4) Finally, last but not least, I think that one part of the puzzle so far not entering into the debate, at least not in the forum between advocates and sceptics of a cosmic explanation for the Younger Dryas, is the very important alternative theory. Still favoured by many scientists, the slowing or cessation of the North Atlantic ocean circulation must also be more critically reviewed as a suggested cause. I think that with just a little digging so many problems exist with this hypothesis, that then should permit the cosmic explanation to begin to gain more favour.

- Rod Chilton