Wow. I give up!
When my [soon to be ex-] pal Iain Davidson suggested I get in touch with my inner PalaeoIndian and investigate the Younger Dryas (YD) Boundary (YDB) Impact Hypothesis (YDBIH), I stupidly assumed that it would be a question of sedimentary context, or of association and datable material, or something equally mundane. Was I wrong? IMHO, you might say so.
As it turns out, my spider senses are telling me that this one isn’t going away for a while. Not because there’s inherent merit in the near-earth-object collision idea. Rather, it appears as if there’ll be claims and counterclaims ’til Hell won’t even have ’em. One side says ‘I see nanodiamonds!’ The other side says, ‘I see dumb people who wouldn’t know a nanodiamond if it fell out of the sky and landed smack on their iris.’ One side says, ‘Nyah!’ Then the other side says ‘Nyah, nyah, nyah.’ I’ll admit, this might be an overly simplistic portrait of the circumstances.
Take nanodiamonds. The proponents of the impact hypothesis claim that they find significant numbers of them wherever they look at the Younger Dryas lower boundary. Great. What’s a nanodiamond? How do you know when you’ve got ’em? Are they truly of extra-terrestrial origin and do they never form on Terra? Good questions all.
Apparently they’re ubiquitous in space, the result of fullerene (a form of carbon) ‘onions’ that form naturally and that when deformed by collision reform in such a way that nanometer-scale diamonds are created–by the trillions per cc of interstellar dust. [I’ve seen so many abstracts and summaries in the past few days I won’t even try to ferret out the source(s) of this facet *cough* of the YDB question. But the statements I’m making are based on published research from so many journals with arcane titles like Glacial Geology that my poor little brain is spinning faster than a quasar.] Nanodiamonds can be synthesized in the laboratory, and they’ve been found in meteorites. The jury’s still out as to whether nanodiamonds of extra-terrestrial origin could collect in a particular stratum of a column of unconsolidated sediments in the western United States.
Someone claims to have found a ton of nanodiamonds at the YDB in the Antarctic ice cap. Someone else says that those ‘yahoos’ sampled a thin profile at the edge of the ice sheet [not unequivocally in primary context, in other words] and don’t even have a well-supported date for the material! Whom to believe? Nanodiamonds may not have spelled doom for the sabertoothed cats. But they’ve sure killed any idea that I might be able to mount a critical examination of the impact hypothesis without about three more graduate degrees.
The same is true of the claims for peaks of carbon microspherules at the YDB. Carbon microspherules? Yep. Some say they have ’em at the YDB. Others say those people are seeing fungal spores and misidentifying them. someone else says they found one on their residential mailbox. Sheesh! All I know for sure is the objects that are being reported are DEFINITELY spherical!
‘He said; she said’ would be preferable to this supposedly empirically based back and forth. How’s a girl to cope? Any judge would throw this out of court before the first recess.
No big impact crater? No problem. The inferred object hit the Laurentide ice sheet, creating a continent-sized splash and a freshwater flash flood of Armageddon-like proportions (which also helped to reverse the global warming that was occurring at the time in the Northern Hemisphere). Imagine the swimming-pool sized globules of water that would have been emitted from the point of impact (sort of like the peaks of the milk ‘crown’ that you see in those instantaneous photographs of drop-sized splashes). These are what some argue created the elliptical, lake-sized, Carolina Bays (which visible in numbers across the eastern continental plain most densely in the Carolinas, but which are also seen in the southeast and even in Nebraska. Their long axis orientations unambiguously point back to an area just north of the ice margin near the present-day Great Lakes). These, some claim, are the shallow ‘splash’ scars left by the house-sized globules of water thrown up by the ice-centred impact.
No impact at all? No problem. Simple. It was a north-south vectored near miss that created a continent-sized ‘airburst’ that vaporized everything in its vortex down to the surface (like the Siberian devastation in the early 20th century that resulted from a NEO NOT impacting the surface–a cometary fragment, it’s assumed). Charcoal from the presumed resultant wildfires that would have been produced in vast quantities across the west of North America south of the ice sheets, and putatively ended up in the so-called black mats found at dozens and dozens of archaeological sites at 12.9 ka. Moreover, the cloud of vapour and dust that would have resulted would have lingered, it’s supposed, long enough to have created a short-lived ‘nuclear winter’ called the Younger Dryas.
Then somebody else says that in fact the YD is effectively invisible in the Antarctic ice sheet, suggesting that this was a Northern Hemisphere phenomenon resulting from the disproportionately large volumes of fresh water emanating from the North’s vast ices sheets, which took some time to equalize and which stalled or reversed the effects of terminal Pleistocene warming for the duration of the YD.
To my way of thinking, despite all of the back and forth, all of the bluster, and all of the details associated with the various lines of evidence, and regardless of the constituents of those black mats, their undeniable presence at the YDB in site after site across the western US and directly to the south in Mexico is a phenomenon that begs explanation. As I’ve indicated in the preceding paragraphs, it’s still an open question what they contain, and if, at the end of the day, those constituents are found to be the unique result of an encounter with a NEO. But the answers must be found, and the mystery put to rest.
And I’m sad to ask: ‘Who am I to adjudicate the contrary claims? Especially since my pocket SEM crapped out the other day and I can’t afford a new one! Oh, and, by the way, I’m not a nanogeologist [not many are, I’m guessing]. On the basis of my ‘investigation’ of this matter, I’m calling for an international consortium of scientists possessing the requisite expertise who have NO vested interest to undertake a large-scale investigation of this phenomenon–from, as it were, the ground up.
The Younger Dryas Boundary Impact Hypothesis is Going Into the Too-Hard Basket
Wow. I give up!
6 thoughts on “The Younger Dryas Boundary Impact Hypothesis is Going Into the Too-Hard Basket”
Impact and human evolution is a pet subject of mine, as I more or less have a background in both the fields of archaeology (my PhD) and as a semi-prof amateur in small solar system body research (I even discovered a NEA).
The problem with the YD impact hypothesis is that the initial evidence for it (and indeed, still almost all of the current evidence) is based on “novelties”. I.e., none of the proposed “impact markers” were recognized as such (as markers pointing to impact) before Firestone, West et al. brought them up as possible evidence for cosmic impact. This while the professional impact research community has a set of criteria to recognize such events for years. None of these established criteria is met by the YD impact hypothesis. That should sound warning bells.
At the same time, the archaeological and paleontological aspects of the hypothesis are problematic as well: many paleontologists would take issue for example with presenting the disappearance of mega-fauna from the America's (or the Late Pleistocene worldwide in general) as a short punctuated event near 12.9 Ka. The same goes for the archaeological side of the story: is the end of Clovis really a punctuated event at 12.9 ka? And even if it is, does this point to extinction, rather than cultural change? I.e., is there really evidence of a dramatic demographic break/discontinuity at the Younger Drias boundary, archaeologically? (note: I am not a N-American paleindian archaeologist, so I have no vested opinion on this question). That the Younger Dryas represents a clear and severe climatological fluctuation, enough to disrupt human presence, is beyond doubt. Central issue is therefore the cause, so even if there was a break in human presence, that still does not prove a cosmic impact, as there are alternatives.
The absence of any clear impact crater does present a problem. With an event of the proposed size, and this young an age, that still should be visible. Impact in the ice sheet going “unnoticed” is not a viable explanation: a large object as this would penetrate through the ice sheet and excavate a crater in the bedrock below the ice. Air-burst? With an airburst of this magnitude, one would expect melt-sheets (impact glasses), geologically visible traces under the airburst location. None of this is in evidence. The Carolina Bays really fall short.
In my opinion, the evidence presented is ambiguous at best, i.e. a far cry from meeting acceptible standards. Non only does it all concern non-recognized “novelty” impact markers, but in addition the reality of most of these are in dispute – the nanodiamonds are not nanodiamonds according to some researchers, the carbon spherules can have multiple origin and it is highly disputed whether they really concentrate heavily in the YD horizon as proposed. Etcetera. And the proposed mass exinctions are not that sudden at all.
As far as impact and human evolution are concerned, there are more interesting cases – the formation of the Australasian tektite strewnfield 0.8 ma ago in SE Asia for example (see appendix to my 2003 PhD dissertation). That that one is due to a genuine large impact, is not in doubt at all – and Homo erectus was already plodding through Asia at that time.
Clarification: I have some contacts with some of the YD impact hypothesis proponents, I am even involved in an attempt to organize a conference on impacts and humans together with these colleagues. I do however not share their enthusiasm for the YD impact hypothesis, for reasons outlined above. Yet, the subject of large impacts during human evolution is an interesting one, worthy of attention.
Thanks, Marco. Would you have any objection to my putting this up front as a guest post? It's certainly a more informed assessment than mine ever promised to be!
Rob, Mail me at my e-mail address and I'll mail you an editted, larger version including more sources
Welcome to the Younger Dryas asylum. The Hotel Laurentide! You can check in, but you can never leave.
There is also this.
Which 'this' are you referring to? When I click I see a bunch of lakes to the south of Lake Nipigon.
If you can't see it, then it's not there. Some people can see it and others can't. It's a pattern recognition thing.
Are you familiar at all with the YD Glacial Lake Agassiz rerouting controversy? That would be a start.
The YD impact is a minor player, the only way it could have had any paleontological impact is if it broke an ice dam releasing an already overflowing Lake Agassiz.
I don't claim that happened, it's just a possibility I looked at.