Sunday, 29 April 2012

Cultural Deposits in Homogeneous Natural Sediments VS. Homogenized Cultural Deposits in Natural Sediments

     Thursday's touchstone blurt has prompted three interesting comments--two of which from long-time acquaintances; one of which was left by Edward Harris, progenitor of the Harris Matrix and author of Principles of Archaeological Stratigraphy [which the author has made freely available online--just click on the title]. 

     All three expressed dismay that any archaeological sites are still excavated in arbitrary levels, and they all added a gentle prod to the effect that I should not be so quick to accept the practice's continued use, even for sites in California. The problem really boils down to this. California archaeologists aren't dealing with cultural deposits in homogeneous natural sediments. They're dealing with completely homogenized (bioturbated) natural sediments and cultural traces. That's quite a different story, as I'll argue further down. But right now: nail buffing time.
     The Matrix man [or so he calls himself] sent me an email in addition to leaving a comment on Thursday's blurt, which I copy here for posterity
Hello Rob
Thank you for your kind remarks and I made a comment on your interesting blog.
How can we advance the revolution (the Matrix is 40 next February!). Perhaps I should learn how to do a blog.
Anyway, I was speaking with colleagues from Playa Vista in California, who suggest they could not have done that dig without the matrix!
Here is the first one ever made and also a little article. You can post them if you like. The first-ever Matrix (read, as we now know, "stratigraphic sequence") was made in 1974 for the site excavated that year at the south gate into the Roman town of Winchester, England.
Edward C. Harris, MBE, JP, PHD, FSA, Executive Director

Cell: (441) 704-5480; eMail:
National Museum of Bermuda
Incorporating Bermuda Maritime Museum
Street: 1 The Keep, Sandys MA 01, Bermuda
Mailing: P.O. Box MA 133, Sandys MA BX, Bermuda
Tel: 1 (441) 234-1333    
Fax: 1(441) 234-1735
 To see his article on time and the Matrix, click here
First-ever Harris Matrix--South Gate, Roman Winchester, 1974 (Photo courtesy of E. Harris).
In what follows I'll try to explain (and not explain away) the conundrum faced by every archaeologist in almost any landform and at almost any altitude in California. Here goes!
     Regardless of the characteristics of the parent material on and in which pre-Columbian California archaeological occupation sites have formed, and regardless of the rate of aggradation throughout the period during which the cultural materials were abandoned, there is a Nemesis against which it is futile for an archaeologist to struggle: fossorial rodents--specifically the ground squirrel (Sciuridae) and the pocket gopher (Geomyidae). These animals are prodigious breeders and tireless burrowers. And because they have been present throughout the epoch of human occupation, they have had a universal and profound, time-transgressive effect on the vertical and horizontal distribution of archaeological materials in California sites. This has been documented in numerous ways and in sites across the Golden State. 
     These animals are capable of transporting any clast smaller than their burrow's diameter anywhere from millmeters to (eventually) meters from it original location (if that was, in fact, its 'original' location). At any time they are regularly disturbing the top 50 cm or so. Given their habit of pushing their backdirt upward and out onto the surface, the smaller archaeological pieces 'liberated' in this fashion tend to remain in the upper 10 cm or so. And larger clasts are transported generally downward because over time they are undermined and drop a few cm at a time. This can happen to boulders and everything smaller that can't be displaced along the burrow itself. 
     The habits and ubiquity of these rodents have ensured that no site in California, and certainly no site with a longish occupation sequence, can be expected to present observable stratification or, for that matter, a vertical column that contains the oldest traces at depth; the youngest near or at the surface. Moreover, the process size-selective upward and downward displacement I've just outlined means that in general there is a bi-modal vertical distribution of artifacts and natural clasts.
     Donald L. Johnson's three drawings below illustrate what can and does occur as a matter of course in (quite literally) any unconsolidated dirt anywhere in California with the exception of [and I'm guessing here] the area above the tree line. It's necessary to read the detailed figure captions to make sure you understand what's going on in each series. However, I'm certain that those of you who aren't from around here will be astonished and might eventually come to accept why it is no surprise that arbitrary levels are still the state of the art in California.
Johnson. Donald L. 1989. Subsurface Stone Lines, Stone Zones, Artifact-Manuport Layers, and Biomantles Produced by Bioturbation via Pocket Gophers (Thomomys Bottae), American Antiquity, 54,  370-389.

In most non-shell-midden sites in California the average stratigraphic profile records only the following:
a. the position of the large clasts that weren't released during excavation.
b. the presently visible rodent krotovinas
c.  a humic layer at the top of the sequence that represents where the latest decomposed vegetation has resulted in illuviation
d. any pedogenetical horizonation that may still be in evidence below where burrowing has occurred, which is often the case in what are known as 'prairie soils' in relatively xeric landscapes, where illuviation of carbonates creates a relatively rodent-unfriendly consolidated layer at depth. 
That's it!
     Alas! There's no remedy for the effects of burrowing rodents on most archaeological sites in California. In fact, the effect I've sketched here is so widely distributed and such a virtual certainty that when attempting to ascertain the extent and time-depth of most pre-Columbian occupation sites savvy archaeologists know that one is most likely to find an example of every temporally sensitive cultural indicator smaller than the diameter of a rodent burrow in the top 10 cm of the site, regardless of the age of a site's cultural sequence.
     Such is life in California archaeology. I'll stand up for my California colleagues any day when there's any question of the professionalism evinced by excavating in arbitrary levels. There's no other choice. We who've worked in California know full well that there's little point in digging a unit to 'sterile' in a site that's been subject to rodent bioturbation. We know that, more than likely, all we're recovering is bagfulls of out-of-context cultural artifacts.
     My new, but long-admired, colleague, Edward C. Harris, MBE mentioned that the people who worked at Playa Vista in southern California told him they couldn't have done their work without using the Harris Matrix. I'd be willing to bet any money that they were referring to their excavations of the historic remains on that massive project, and not any pristine (nominally speaking) pre-Columbian occupation sites.
     This has been fun. Have a good week, everyone.

Working On The Implications Of Homogeneity VS. Homogenized

I know I've been blurting very spottily of late. Long story.
    But I assure you, I'm busily preparing a treatise on the difference between homogeneous and homogenized natural sediments, in the hope of restoring some of my credibility as an ethical and sensible archaeologist where it concerns excavation techniques. As you may have seen from the comments on my Thursday blurt, there is some understandable push-back with respect to my readiness to accept the persistence in California (especially) of excavation using arbitrary levels. I hope to reassure my colleagues outside of the region of the archaeologist's obligation to accept the reality of ubiquitous and catastrophic bioturbation almost everywhere in the Golden State.
     Please stay tuned. 

Saturday, 28 April 2012

This Could Change Everything...

Once in a while you hear of ground-breaking research. One of my officemates just showed me an announcement of her son's recent isolation of a 'silencer' gene.
Unbelievable. The Nobel Prize awaits. Click and see. Amazing.

Scientists find the structure of a key 'gene silencer' protein

Scripps Research Institute scientists find the structure of a key 'gene silencer' protein
Scripps Research Institute scientists have found the structure of Argonaute2, which can effectively "silence" a gene by intercepting and slicing the gene's RNA transcripts before they are translated into working proteins. Credit: Image courtesy of the MacRae lab, the Scripps Research Institute.
Scientists at The Scripps Research Institute have determined the three-dimensional atomic structure of a human protein that is centrally involved in regulating the activities of cells. Knowing the precise structure of this protein paves the way for scientists to understand a process known as RNA-silencing and to harness it to treat diseases.

Friday, 27 April 2012

Touchstone Thursday: Edward Harris's Principles of Archaeological Stratigraphy

I swore to myself that I wouldn't let another Thursday go by without a touchstone. This is me living up to my own expectations!

2ed 1989 Academic Press
For [I think] the first time since I began this Thursday ritual, thanks to E. Harris I can talk about it and you can all have access to an electronic copy for your libraries. Bonus! I discovered that he's providing it as a free download at for nothing more than a few bits identifying you and some information as to why you're interested in it. 
     Before I get too far, I have a confession. I've never put Harris's concepts into practice. With but one exception, every project I've participated in employed arbitrary horizontal levels (AKA 'spits'). That is the practice against which Harris placed his Principles of archaeological stratigraphy. Unfortunately, to employ the principles of archaeological stratigraphy, you have to have a stratified site. Harris's great contribution was his insight that, to interpret a stratified site--especially any that are more complicated than a layer cake--you need to pay attention to the relationships of all the various layers with respect to all the other layers. This is often a tall order.
     I can completely understand why my friends doing California archaeology are precluded from relying on Harris's concepts for interpreting most of their finds, since most of the countryside at nearly all elevations has been totally and is continually reworked by burrowing rodents. I can also understand my colleagues who excavate in caves and rockshelters, especially those whose deposits are almost entirely autochthonous (i.e. deriving from the cave itself), since for the most part these deposits are a uniform color and therefore it is frustrating if not futile to attempt to dig in natural levels. 
     I find it fascinating that this book is and has been for some time out of print. Can we presume that the practices that Harris touted have become part of the archaeological zeitgeist to such an extent that it's second nature and the book's no longer needed? I doubt it.      
     It's no surprise to me that the biggest users of the Harris matrix (the official name for Harris's brainchild stratigraphic notation and analytical device) are historical archaeologists. They deal much of the time with horizontal, or at worst barely sub-horizontal features and levels--walls, prepared floors, and so on. These are also the kind of sites that don't require sedimentological or geomorphological interpretation--especially in urban settings the likelihood of natural deposition is low.
     I think my fascination with Harris's Principles is that the philosophical terrain he travels is a lot like a foreign country to me. It's like Harris's is the medieval notion of the organized and ladder-like Great Chain of Being and what most of us are used to dealing with is like the messy and complicated natural world of Darwin. It's depressing to think that any site I'm likely to see in what's left of my career is gonna be Darwin-like! It would be refreshing to experience the rigor of following a level across a wide-area excavation. I'm sure it would be rigorous, but rewarding. 
     If you give this book a close reading you'll find much that's insightful and foundational. And just because you might end up digging 10-cm deep site-testing squares 'til you choke, at least you'll be armed should you ever be so lucky to need the knowledge this book contains!
     I think I'll turn in now.     

Tuesday, 24 April 2012

Can You Say Reprehensible?

I suppose it'll come as a shock to no one. The leading source of business news for the 1%, the Wall Street Journal, ran a story recently about TEFAF, the annual fine art and antique fair in the Dutch city of Maastricht that's put on by the watchdogs of art on 'the continent,' The European Fine Art Foundation. I'm singling out for deprecation the TEFAF, its exhibitors/dealers, and the WSJ reporter because of the kind of 'art' that it and the paper are pimping.
     I was drawn to the article by a link somewhere that showed this (putatively) Olmec jade mask [clearly meant to be worn by its two-legged primate carver or the owner thereof] and proclaimed that it had been sold for 1.75 million (a lot of money).
Wall Street Journal online: 'In the Eye of the Beholder' March 23, 2012 
All of my archaeologist friends will cringe at the thought, to begin with. But if they're like me, the cringe will transform itself rapidly into closed fists and rage.
     This is how one 'dealer' explained his situation vis a vis the Olmec mask.
Meanwhile, ... a powerful, life-size mask in blue-green jade by the Olmec people of Guatemala in 900-300 B.C. captures the eye. Representing an owl man, the haunting, supernatural creature has both human and bird-like features... . "We waited hopefully for ages before contemporary collectors moved into our market," says Bobbie Entwistle." And then it happened in the last three years." Her partner, Lance Entwistle, notes that pieces at the high-end are doing particularly well, as big contemporary art collectors seek iconic objects. "Unfortunately," he says, "supply is short."
Boo-hoo. Bastards. If the pillage of archaeological sites weren't already a bigger threat to world heritage than the government of Turkey, sales and prices like this'll quickly turn the trade of illegal antiquities into a global turf war for plundering rights. And you thought cocaine was troublesome!
     Only two WSJ readers commented on this travesty of a 'news' story. One brought up the difficulty of authenticating such pieces. True. If there were any real authenticating going on, the dealers must be in possession of the lay equivalent of a chain of evidence going right back to the impoverished, machete-wielding opportunist who hacked a chunk of our heritage from its archaeological context. If so, it should be possible for law enforcement to bring charges of illegal trade in antiquities against each and every pair of hands that touched that piece, all the way back to the Mexican bush-whacker.
     Wouldn't it be loverly? It goes without sayin' that it ain't gonna happen.
     Finally, how oblivious to the ongoing archaeological Armageddon was our thoroughly, editorially ethical, WSJ correspondent? This is how.
Among my favorites were Egyptian pieces. At Rupert Wace Ancient Art of London, a rare Egyptian relief with an image of Queen Hatshepsut, who was the first woman to rule Egypt in her own right (1479-1458 B.C.), was quickly snapped up for a six-figure sum. "From the first day, we had lots of sales," says Swiss ancient-art dealer Jean-David Cahn. Among the pieces that went immediately were a small head of a bald Egyptian priest, from 728-525 B.C. (price: €62,900); and an exquisite, serpent-shaped, gold Egyptian bracelet, from the second century B.C. (price: €29,600). Such bracelets decorated the upper arm of Hellenistic statues of Aphrodite in Alexandria.
Hatshepsut, fer Chri... in' out loud! And only six figures! These people may be vipers. But, they wouldn't know a seriously important artifact from a large hole in the ground [about which us archaeologists know a great deal more]. You do the math. A jade mask of some nameless faceless Olmec owl-man garners almost twice as much as what amounts to the equivalent of a previously unknown signed da Vinci! [I hope you realize I'm only making a very bad joke--but the analogy still holds.]
     To summarize, Jeebuz! We're all in trouble with this much slam-dunk ignorance and avarice abroad in the world.

Monday, 23 April 2012

I Forgot My Own Semianniversary!

April 5th was the 6th month-a-versary of the Subversive Archaeologist. Imagination that! 1183 views the first month. 1458 the second. Then 2270, 3110, 6252, 8598, and 5332 so far this month. More than 9000 unique visitors since Feb. 7!
     Anyway, I just wanted to say I wouldn't have made it anywhere near a semianniversary without ALL of you great people who read my blurts, whether just one or every one, whether friend or detractor, looney or otherwise [that'd be a lot of my personal friends ;-)]. I won't say I couldn't have done it without you; I wouldn't have done it without you. I spent the first twenty or so years of my so-called career preaching to a very small choir. Without readers this little project of mine would have been worse than futile. THANK YOU, EVERYONE!!!!
     For your sake I hope my best work is ahead of me! In the meantime, your support truly means a great deal to me [most of you probably have no idea]. 
     In that vein, with my field excursion to Czechland around the corner, I can promise you one thing. You'll see a different perspective once I get out of my pajamas and vacate my mama's basement! ;-)

Sunday, 22 April 2012

People Who Live In Glass Houses Should Not Stow Thrones

     Here's a real beaut of a story that brings to mind any number of aphorisms to remind the arrogant of their essential hypocrisy. 'The pot calling the kettle black' comes to mind. As does the epigram I've bent to my own uses in this blurt's title, 'People who live in glass houses should not throw stones.'
Turkey: To Regain Antiquities, Ankara Plays Archeological Hardball (
It seems that Turkey, last remnant of the once great Ottoman Empire--the longest lived in history--is turning its gaze outward and flexing its nationalistic muscle in the hope of reclaiming some of its splendid ex-pat artifacts abiding in foreign climes, including the Altar of Zeus from the ancient Greek city of Pergamon (located in what's Turkey today). 

     From Newsweek comes this:
The Turkish government has decided that it can score nationalist points by launching a vocal campaign to recover ancient Anatolian artifacts from foreign museums. Over the last year the Turkish Ministry of Culture and Tourism has resorted to ever-more aggressive measures, from threatening to suspend the excavation licenses of foreign archeological teams to blocking the export of museum exhibits. Last month, for instance, the ministry announced that it would not issue export licenses for several dozen museum pieces due to be displayed at the Metropolitan Museum of Art in New York, the British Museum, and the Victoria and Albert Museum in London. As a result, important exhibitions—Byzantium and Islam at the Met, The Hajj: Journey to the Heart of Islam at the British Museum, and The Ottomans at the V&A—have either had to scramble to find alternative artifacts in non-Turkish collections or delay the exhibitions altogether.
This, while inside Turkey they can't even keep their own chickens from their own home-grown foxes.
Two employees have been reassigned allegedly in connection with a scandal in which the director of Istanbul’s Topkapı Palace Museum ordered a priceless throne to be carried off to his personal residence in June. The decision to reassign two employees, despite an ongoing investigation over the scandal, has raised concerns that the museum’s director is being shielded by the ministry (The Hurrieyet Daily News online).
All of which, to me, begs a huge question. Whose past is whose? The Altar of Zeus was built by the Greeks, who saw nothing wrong with colonizing Asia Minor in the centuries before the year 0 CE. The modern Turks have been something less than autonomous over the millennia. Should Turkey, simply by virtue of its unhappy past, be 'allowed' to claim the Altar of Zeus for its own? 

If this blurt turns out to look and sound much more like a history lesson than a subversive approach to an archaeological question, please bear with me [I do say that a lot. Don't I?] I think it'll become clear that there's nothing clear about who owns the past--at least not in this case [and I suspect, in most such cases]. My conclusion is that the Altar of Zeus should stay in Berlin. Perhaps it should be treated differently given its provenience. But stay there, it should.
The climax of the Ottoman Empire, at 1683. It's decline began thereafter, as European powers expanded their reach, especially Austria. The remainder of the empire was dismantled in 1924 after its final defeat in the First World War. Its capital was Constantinople (modern-day Istanbul). From Wikipedia
The lands comprising today's Turkey, as everyone probably knows, sit at the crossroads of continents, and were variously colonized or occupied by more classic, medieval, and more recent civilizations than I or anyone else could shake a stick at. Hattians, Hittites, Assyrians, Chaldea, Phrygians, Cimmerians, Lydia, Caria, Lycia, Achaemenid Persians, Greece, Rome and its successor, Byzantium (the rump remains of the Roman Empire). 
The Eastern Roman Empire (Byzantine Empire) at its height. (Wikipedia)
By 1071 CE what's now Turkey had been subsumed by the Great Seljuq Empire, which was a Sunni Muslim power marginal to the Great Caliphate, the Muslim empire against which Europe crusaded in the Middle Ages (Seen below). The Seljuqs ruled for about 300 years. 
The Caliphate (the Muslim World) in 750 CE. Note that in this period Turkey is still part of the Eastern Roman Empire (Byzantium). Wikipedia.
Their influence on religion in Turkey was profound and remains so to this day. 
     The pan-Asian Mongol empire was the last hegemonic power to which Turkey was a vassal prior to the indigenous rise of the Ottoman Empire. The Khans conquered all but a small portion of what's now Turkey--only the extreme western part remained independent. The last Mongol ruler of Turkey will be well known to most of you--he was Kublai Khan, direct descendant of Genghis, the man who single-handedly invented world domination. Prior to the modern era, there was none that covered more territory. 
     The Ottoman Empire recouped the rest of modern Turkey in the waning years of the Khans, and, as you now know, the polity based in Constantinople endured into the 20th century. Following the war that ended no wars, the Ottoman Empire was divvied up in 1923. Here's what became of the great Ottoman Empire after WWI.
Yet more Wikidpedia!
     You'd think that such a polyglot history would be acknowledged and embraced by the modern government of Turkey. You'd of course be wrong. Nothing is ever as it seems or as it seems reasonable to assume it should be [another fearless subversive aphorism, if you wanna know]. 
     The palatial artifact  you see below is the Altar of Zeus that began this story, removed from the Greek acropolis at Pergamon. And Turkey wants it back. It was liberated by German archaeologists in the 19th century, after an agreement with the then government of Turkey. If you want to know just how prominent an artifact this was in the ancient city itself, check out the lithograph representation of the Acropolis at Pergamon in its heyday, immediately below the contemporary photo that shows its immensity [to say nothing of its Greek-ness].

The Altar is the building that has the smoke drifting skyward from its roof. 
     In the case of the Altar of Zeus, who owns it is no trivial question. Do the modern Turks have any claim, natural or otherwise, to this trace of ancient times? Who are the modern Turks? You'd have to say that they're culturally well removed from the inhabitants of that part of the world at 500 BCE. Did the 'turks' of that period look and act like the Greeks of that time? Probably. What about the Roman era? After a while, maybe. But maybe not. The Byzantine Empire (the eastern remnant of Rome) actually emulated classical Greek culture for a few hundred years. Does that give the modern Turkish people the right to the Altar of Zeus? Who are the 'Turkish' people? 
     I think you know what's going on in Turkey when its present government plays 'hardball' with its past. They know that history's an hourglass glued to the table, regardless of whose history we're considering. Whose interests are being served by their intractability at this time in history? Certainly not the Past's. This is not a question of who owns the past. This push to repatriate is not born of ethics, nor should it be decided on the contemporary notion of ethics. And, most importantly for you and me, this is not a question of archaeological ethics.  Notwithstanding the depredation that occurred in the first place, I'm fairly certain that the German museum takes its stewardship of the Altar of Zeus very seriously, and its integrity as an artifact is all but guaranteed. 
     So what's all this about? And how do you solve the matter equitably? Well, for starters you don't acquiesce to the Turkish demands. It's curious that the Turks are concerned about their Greek antiquities. Given the very long history of antipathy between modern Greece and modern Turkey, you might think that the Turks would be happy to see 'their' Greek antiquities thrown in the dumpster.
     Or is this about Turkey sticking it in the eye of Greece for political points? The modern-day Turkish government, nor the people it claims to represent have no claim, and no right to claim, that the Altar of Zeus belongs to the modern-day country of Turkey. Period. No more, as it happens, than the European occupiers of the Americas have any claim to the remains and the cultural treasures of the indigenous people that they've displaced. 
     As it happens, Germany, in this case, has a contractual arrangement that allows them to claim, legitimately, the artifact as their own. But that, too, is a historical artifact. Who're you gonna call? Who owns the Altar of Zeus? Not I. Not you. Not Turkey. Not Greece. Not Germany (which, of the three, has the least logical claim, cultural or otherwise). What of the Mongols? The Sunni Muslims? The Persians?
     I think you'd have to say that, under the circumstances, one could easily and justifiably claim that the Altar of Zeus is a part of the world's heritage. Regardless of where it presently resides, at some level it belongs to all of us (as indeed do all of the works of humanity, going back into the Pleistocene). UNESCO could quite easily designate it to as such and in so doing be able to dictate the terms of its curation, and the member nations of the UN would be forced to abide by the rules as set forth in the UN Charter. I say, to Hell with 'em if they don't like it. In the case of the Altar of Zeus the laws of ownership went out the door before the year dot.
     The last thing I want to see any of the world's governments do is pander to one government or one people to the detriment of the rest so that the government 'playing hardball' can profit from its transparently nationalist politics. In the end it boils down to this inalienable travesty--whoever owns the present owns the past. And if one government or another acquiesces to Turkey's muscle-flexing, it'll have more to do with maintaining ownership of the present than it has to do with who, rightfully, owns the past.
     I think we should ignore the pants off Turkey.

Induced Torpor

noun \ˈtȯr-pər\

Definition of TORPOR

a : a state of mental and motor inactivity with partial or total insensibility
b : a state of lowered physiological activity typically characterized by reduced metabolism, heart rate, respiration, and body temperature that occurs in varying degrees especially in hibernating and estivating animals
: apathy, dullness
: what happens when the number and kind of problematic issues with which the mind is dealing exceed the capacity of the subversive mind to understand and undermine effectively in the very short time-frame imposed by the blog format. Sometimes leads to forgetfulness, procrastination, insensitivity to the passage of time and missing deadlines long-ago self-imposed.

I'll get back in the saddle. Have no fear. Unfortunately I feed sadness and remorse that I can't feed your hunger for subversion at regular intervals at this time. The phrase 'Too much on his plate' comes to mind. I miss you, too!

Hasta luego. A la prochaine. Na shledanou. See you later.

Thursday, 19 April 2012

Putting Their Feet to the Fire

I'm at work on a 'who owns the past' rant, but I can't forbear mentioning that I'm getting rather hot under the collar having to read all these headlines about 1 million year old cooking fires in South Africa (to say nothing about numerous similar claims from more recent parts of the Pleistocene). You'll probably think I'm batshit crazy even to think of tackling the issue without two degrees in organic chemistry, however I promise you that you'll be hearing from me in the near to medium term. I truly wonder if natural processes have been adequately considered and if not, they can't be ruled out. Stay tuned.     

Tuesday, 17 April 2012

A Human Evolutionary Battle of the Technological Titans for the Undisputed World Heavyweight Championship of Nest Building: Castor Canadensis VS. Pongo pygmaeus

Round 1: In which Pongo makes a nest (Credit)

In the world of ethology one group stands head and shoulders [well, head, anyway] above the rest--primatologists. Unlike their scholarly kindred primatologists can make a claim that's unique among those who study animal behaviour. That is, they can always justify their days spent grunting, hooting and chest beating, and walking about on all fours so as to acclimatize their subjects to their presence by arguing that they are investigating behaviours that might [a mighty might, that] have a bearing on our understanding of how humanity dragged itself up out of the primordial muck savannah dust to stand erect and eventually to free its hands for tool making or rickshaw pulling and in the process enslaved its feet, qua pedal extremities, qua locomotory appurtenances, forever [credit goes to my old acquaintance Gary Richards for that bit of podial insight].
Jane Goodall in the early 1960s
     Indeed, since the time Dame Commander of the Most Excellent Order of the British Empire Valerie Jane Morris-Goodall removed herself from her (probably girlie) English roots to insinuate herself into Pan trogolodytes (chimpanzee) society on the shores of Lake Tanganyika at Gombe, revelations about the human-like behaviour of the great apes [other than humans] have punctuated an otherwise brutally hot, sometimes deadly, but always physically and emotionally difficult vocation. 
Gombe (© 2003 National Geographic Society. All rights reserved.)

Dame Goodall has shown us that chimps pull the leaves off of twigs to enable them to reach into termite mounds to attract termites for consumption [or did some oblivious ranch-hand inadvertently show one of them how to do it, resulting in a new 'tradition' amongst the group?]. Crumpling leaves to make sponges to extract water from puddles also emerged from the studies at Gombe [so, too, did brutal rape, torture and cannibalism of fellow anthropoids, but we won't dwell on that. At least we can be certain that it wasn't the same oblivious ranch-hand that taught them those things...].

     And yesterday comes fresh news of the startling cognitive capabilities of a great ape--Pongo pygmaeus, the orangutan. This animal is, by all accounts, something of a nest-building, evolutionarily precocious, civil engineer! van Casterena et al.'s 'Nest-building orangutans demonstrate engineering know-how to produce safe, comfortable beds' [published online before print April 16, 2012, doi: 10.1073/pnas.1200902109, Proceedings of the National Academy of Sciences of the United States of America (PNAS)] brings us face to face with ... ourselves [albeit about 12 million years in the past]. Like the good anthropologists the authors are, they've thoroughly anthropomorphized this animal's actions by deeming it 'engineering' and saying as much in print, in a scholarly journal [albeit one about which there are serious questions as to the seriousness of the review process]. This adds to the long list of claims made in behalf of science [the list I've just alluded to] for the other members of what's come to be known as the Homininae,* the Linnaean Family that includes you and me.
But, before you get too caught up in the weltanschauung of willy-nilly anthropomorphizing that permeates higher primate studies, let me bring you back down to the ground. Remember this little furry rodent? Castor canadensis? They build 'nests' too! Only theirs are permanent, unlike those of primates [which are constructed from scratch at least once a day], and are sometimes fairly large structures. Did I say 'fairly' large?
One recently observed in Alberta is an incredible 850 metres long! That's about half a mile! Have a look! Like the Great Wall, you can see this thing from space (thanks to Google Earth). These piccies are from a MailOnline article touting the [ahem] 'engineering' capabilities of this relatively small-brained, furry creature.
The brown area has been denuded by Beaver logging. The water flow is toward the top of the picture. The arrows point to two beaver lodges (themselves quite elegant feats of 'engineering'). There must be myriad smaller ones, considering these ones, too, can be viewed from a satellite orbiting the Earth!
Giving credit where credit is due, the lead author of the orang nest article did say this in an interview.
'We think the skills you'd need to build such a sophisticated nest are on a par with those you'd need to make and use tools, so require a similar cognitive ability. In this context, it would be interesting to investigate nest-building by other animals like beavers and birds,' says van Casteren [click here for the full story of this quote].
I wonder what they'd conclude from a 'study' of the other nest builders. Chances are it won't be that our closest relatives are on a par with beavers and bower birds. Nuh-uh. They'll be lumping beavers and beaked dinosaurs with humans and the other great apes! I mean, really, what else can you say, on present understanding, than that most mammals are capable of some very complex behaviours, that are often, in part, learned from conspecifics. So, it seems, are birds. So are bees and mud wasps. So, too, are web-building spiders! If you wanted to take this whole anthropomorphic engineering meme to its logical conclusion, you could probably see evidence of cognition on a par with humans in the colonial habits of some single-celled organisms. Where does it stop?? 
     If I had my 'druthers it would stop here, with the sensible conclusion that our closest relations are clever mammals. Full stop. Let's face it, the nesting behaviours we're witnessing amongst, for example, Pan and Pongo were probably extant at the time of the last common ancestor, so we're not talking about some inevitable trajectory from nest building (however 'clever' it might seem to us primatologically impoverished humans) to modern human cognitive abilities--such as the ability to understand what these pixels are meant to mean to you. And even if we could possibly understand what it takes in the way of brain function to make a bloody orangutan nest, all we'll have done is identify an ability that's (conservatively) about 12 million years old. So. What!
     I think the study of our primate relations is important (if only 'cause they might not be around forever). But let's get serious about the implications of what we observe.
     I'll now go back to my torpid state.

* I, however, will continue to refer to this small group of extant and fossil forms as belonging to the Superfamily Hominoidea, and to the Families Pongidae, and Panidae, Gorillidae and Hominidae. Unlike so many of my siblings in the biological/physical anthropology clade of the academy, I'm not taken in by the vocal claims of the primatologists that certain behaviours amongst our closest genetic relatives makes them any more human than they were before Johnny Weismüller and Cheetah cavorted in the treetops together before Jane came along [all churlish innuendo intended!] Thus, I am not convinced by the recent, arbitrary revision of the Superfamily Hominoidea, and I will cleave to the taxonomy I've just outlined until either a) someone persuades me to think otherwise, or b) I expire.

It Gives Me Pause to Consider

hi·a·tus /hīˈātəs/

A pause or gap in a sequence, series, or process.

gap - lacuna - blank - chasm    

Sunday, 15 April 2012

Just found a really handy app

     It's called Evernote. It's free. I just 'clipped' a web page on my desktop and, thanks to iCloud and Evernote's syncing functionality, the web page is on my iPad as a note. I can now take my iPad into the kitchen, stand it up and use it as tonight's cookbook. Effing marvellous, I say! [Please forgive me if I think that the intertubes and computers are finally being sensible about data. Almost 30 years later. But at least I get to play more efficiently before I die!]

Never on a Sunday?

     Crikey! Sunday. Hay mucho trabajo a mi casa hoy. Los deeshes. La lavanderia. Los pisos. La uña (Las uñas?). Y mucho mas. No blogo a hoy. Creo que "asta mañana".

Thursday, 12 April 2012

Touchstone Thursday*: Luis W. Alvarez et al.'s 'Extraterrestrial Cause for the Cretaceous-Tertiary Extinction'

This may seem like a bit of a dereliction of my Thursday duties. But, under the circumstances I thought I'd bring back a real classic published in Science back when big hair and Genesis were de rigueur. This one is about the shot that nobody in the world heard because it happened 65 million years ago. Then-retired UC Berkeley geologist Luis W. Alvarez, his son Walter, Frank Asaro and Helen Michel conspired in what became a paradigm-shifting, figurative tsunami in the geological literature (and in the zeitgeist of every geologist from here to...well, probably...Timbuktu!). 
     'Extraterrestrial Cause for the Cretaceous-Tertiary Extinction' and the deluge of scholarly papers that it spawned are the direct ancestors of the Younger Dryas Boundary impact hypothesis, about which you've seen much at the Subversive Archaeologist in the past week.

[Back in 1980 I was a library clerk at Agriculture Canada's Vancouver Research Station, still several years away from beginning an undergraduate degree in Archaeology. In those days I still had visions of standing hip to hip with Don Johanson or Richard Leakey while they solved the riddle of the human past. One of the many nationally important jobs I performed was opening the mail. Then I set the incoming journals on the shelf. I fetched. I carried. Anyone with a wry sense of humour will, at this point, note that my career vector is pretty close to uppercase sigma from x=1 to infinity of 1/x. But, as I keep assuring you. I ain't bitter.     
Because of that perch in a science library I was the first to see every issue of Science and Nature. Each week I mined them for anything palaeontological, human or otherwise. As a result I was way ahead of the curve relative to my peers when it came to the Cretaceous-Tertiary impact hypothesis. One of my library clerking jobs was to manage a small satellite library belonging to some agricultural inspectors. They happened to get the Morbidity and Mortality Weekly Report from the CDC.  Sad to say, because of that part of my job I also had early news of a contemporary world-changing phenomenon that promised to decimate the human population--the AIDS epidemic.      I remember clearly reading the earliest scientific reporting of the emerging consensus that there was something linking a large number of opportunistic infections and immunological disorders that had cropped up in (mainly) the American northeast in the wake of the 1976 American Bicentennial celebrations. Among the truly rare diseases that I recall hearing of for the first time was Kaposi's sarcoma--a really nasty form of cancer. I also remember that Candida albicans was almost ubiquitous among the people who were diagnosed with what came to be called 'the gay cancer.' C. albicans causes thrush, a relatively benign fungal infection for someone with a healthy immune system, but became a life-threatening pneumonia for those who were incubating the virus that, much later, would come to be known as HIV.]
With that lovely recollection hanging out there, it's probably going to seem unsympathetic of me to continue with extraterrestrial impacts. But, then again, both AIDS and whatever caused the extinction of the dinosaurs were responsible for the deaths of many millions. Here's hoping we have more luck with AIDS than the dinosaurs had with visitors from outer space.

In 1980 was immediately drawn to Alvarez et al.'s hypothesis. It has always seemed to me that something very, very bad and at the same time something very big must have been responsible for the second greatest 'dying' in the Earth's history. Speading sea floors and disease just didn't do it for me, and the contemporaneous theory that a supernova had destroyed most life on Earth seemed just a little hard to swallow. 
     But the extraterrestrial impact seemed appropriately big and sufficiently bad to satisfy my criteria in the matter, especially if you consider that it the nuclear winter scenario had only just been floated by the anti-nuke movement of the time. So, with my new-found extinction theory in hand, I started talking to people. You'd be surprised how much resistance there was to the notion. I still think it's weird. I'm wondering if it isn't a species of cognitive dissonance, whereby the mind actively tries to downplay an unpleasant idea--e.g. that the earth has been, and will continue to be, bombarded by rocks from outer space forEVER, and that there's nothing to be done except to accept it as a given and try not to get too stressed about it. 
     So, what heresy did Alvarez et al. proclaim over thirty years ago that was so actively resisted in the scientific community. Oddly, I think it wasn't the fact of the impact hypothesis itself that rankled, but rather the proposal that life on Earth was utterly changed as a result. Again, it may have been cognitive dissonance at work. To this day there are many who downplay the role of the asteroid in killing of about 40% of life on Earth, and claim that the extinctions weren't as much of a punctuation mark as Alvarez and others were suggesting.
     It's strange to read this article again after so many years. It's as if the authors were discussing doing the dishes. No spectacle. No hyperbole. Just matter-of-fact and immediately accessible words--even to the non scientist. Listen to what they say about the effect of the asteroid.
In brief, our hypothesis suggests that an asteroid struck the earth, formed an impact crater, and some of the dust-sized material ejected from the crater reached the stratosphere and was spread around the globe. This dust effectively prevented sunlight from reaching the surface for a period of several years, until the dust settled to earth (1105). 
That's that! Oh, there were pages on the evidence, most of which Marco Langbroek outlined in his post on Tuesday--enhanced iridium at the Cretaceous-Tertiary boundary, shocked quartz all over the place, brecciated sediments.
     Then there was the extinctions. People had been debating for decades what might have happened. And rather like the discovery of plate tectonics, the authors' proposal of an extraterrestrial impact made sense of it all.
Loss of sunlight suppressed photosynthesis, and as a result most food chains collapsed and the extinctions resulted (1105).
So simple. So logical. So...expectable.
I'll leave you with the photo below. It's what gave me the idea to put the Alvarez et al. hypothesis in the Thursday spotlight. That's because it's a collection of recent papers about the Younger Dryas impact hypothesis, and like the Alvarez et al. paper, it'll be ten times bigger before all is said and done. 
     Having had a little more time to stew about it, and to nose around in the literature, I'm not sure the impact hypothesis won't stand up when all the data are in. Perhaps it won't stand on some of the 'novel' evidence that's been proposed; perhaps it will. But I think it's a very good place to start if we're serious about explaining the widespread occurrence of Vance Haynes's 'black mats' at 12.9 ka.
Just a smattering of the paper and ink already spilled on the Younger Dryas Boundary impact hypothesis. Seeing it inspired me to recall the progenitor of all such theories--Alvarez et al. 1980 (Credit skepticalscience, which also has a darned good summary of the research to date: click here to see it).
I'll be lifting off for now. Keep your eyes on the sky!

* It's Thursday somewhere already. Publishing this now means that I can take a breather tomorrow [er...yesterday?]!

Tuesday, 10 April 2012

Forced to Take Draconian Measures to Muffle an Impolite and Disruptive Commenter

It seems that we've attracted a persistent and disrespectful detractor. At first I simply blocked comments to the YDB posts to spare you his vitriol. Then he showed up on the post about my daughter and university. Feeling a little threatened by that I decided to switch to moderating all comments. I'm only able to use one email to moderate, and I've chosen my home address. So, on days when I'm at work it'll likely be a while before any useful comments make it to the light of day. It's funny. I had an inkling the moment kT popped up on the comment board. I should have listened to my instincts. Or the voices in my head. One or the other.

Marco Langbroek Guest Comment: The YD Impact hypothesis--far too much impact

Maybe. Maybe not. Not in 2012, at any rate!
After my [you'll pardon the expression] 'crash and burn' on the matter of the Younger Dryas Boundary Impact Hypothesis, I'm very pleased that Dr. Marco Langbroek will contribute his thoughts on the matter. Some of you may remember several exchanges he and I had in the early days of the Subversive Archaeologist. [Can I really say 'early days' if it's only 6 months ago? Somehow it seems a lot longer...]. 
If you're curious, you can call up those old posts using the search window lower down on the left sidebar. Given that history, I'm doubly pleased to have him here today, simply because he has stuck with this blog despite any social imperfections I may have demonstrated in our earlier conversations.

Dr. Marco Langbroek
Marco Langbroek (b. 1970) is a Dutch palaeolithic archaeologist. He obtained his MA and PhD in palaeolithic archaeology at Leiden University in 1998 and 2003, worked as a post-doc researcher at the Institute for Geo- and Bioarchaeology of the VU University Amsterdam from 2008-2012 and is currently affiliated as a guest researcher with the same University.
     Impacts and human evolution are a long-standing research interest of his. In an appendix to his 2003 PhD dissertation he pointed to the contemporaneity of a known large cosmic impact in SE Asia, and Homo erectus presence in Asia (published in 2004 as BAR International Series nr. 1244) .
     He's involved in small solar-system body research as a high-end amateur. He has authored/co-authored a number of peer-reviewed papers in the field of meteor research, and has discovered several asteroids, including the NEA 2005 GG81. The International Astronomical Union has named asteroid (183294) "Langbroek" after him in honour of these activities.
I received this from Marco this morning. Dr. Langbroek pulled an all-nighter to get this ready. We're in his debt.
"Impact and human evolution" is a pet subject of mine. I have a somewhat unique position with regard to archaeology and cosmic impacts, as I have a background in both the fields of archaeology (my PhD) and in small-solar system-body research. In addition to my archaeological work I have authored/co-authored a number of peer-reviewed papers on meteor research, and I've discovered a number of asteroids, including a NEA. These latter activities were conducted as a high-end amateur; I would certainly not claim to be an impact scientist. But I believe I do have more knowledge of that field than the regular archaeologist does.
So naturally, when the Younger Dryas (YD) impact hypothesis was proposed (Firestone, West et al. 2007, PNAS 104, 16016), I monitored the debates that followed with interest. When Rob Gargett brought the subject up on this blog, I had to share some of my thoughts, which led to Rob's invitation to write this guest post.
The Younger Dryas (YD) Impact Hypothesis does not sit well with both the mainstream impact science community, and the mainstream archaeological and paleontological communities. There are clear reasons for this negative attitude. Among the proposed impact events, the YD "impact" hypothesis is a decidedly odd duck in the pond.
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". In essence, almost 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 used a set of unambiguous markers to recognize such events for years. These include the presence of glassy impact ejecta [see below];

True impact evidence: tektites and impact melt glasses from various impact events (collection M. Langbroek). (a) Lybian desert glass, 28 Ma impact over North Africa; (b) Moldavite tectite, 15.1 Ma Riess crater impact; (c) Irghizites, 0.9 Ma Zhamanshin crater impact; (d) Darwin glass, 0.8 Ma Darwin crater impact; (e) Bediasite tektite, 34.5 Ma Chesapeake Bay impact; (f) Australasian tektites, 0.8 Ma Australasian impact.
shocked quartz grains; horizons with anomalous concentrations of Iridium and other elements in deep sea cores, terrestrial deposits [see below] and ice cores;
True impact evidence: Iridium rich clays from the K-T boundary layer, Stevns Klint, Denmark (collection M. Langbroek).

presence of shatter cones in target rock; ejecta blankets; a crater with breccia fill [see below], melts and overturned rim strata etcetera.
True impact evidence: impact suevites and melt breccias from various impact craters (collection M. Langbroek). (a) Riess crater suevite breccia, Germany; (b) Söderfjärden crater impact breccia, Finland; (c) Paasselkä crater impact melt breccia, Finland; (d) Paasselkä crater impact breccia, Finland; (e) Garndos crater impact breccia, Norway; (f) Glover Bluff crater impact melt breccia, USA; (g) Dhala crater impact breccia, India; (h) Dellen crater suevite, Norway; (i) Sudbury crater metal rich impact melt breccia, Canada; (j) Sääksjärvi crater suevite impact melt, Finland.

While these need not be present as a full set, at least some of them should be found before one could posit an acceptable theory that a cosmic impact occurred.
And here is the ringer. None of these established criteria are met by the YD impact hypothesis. The evidence that proponents of the hypothesis have brought up so far mostly concerns the mentioned "novelty" markers (with the exception of a contested Iridium enrichment and a likewise disputed presence of impact spherules, see below). And in addition, the evidence is ominously negative on a number of important impact markers widely recognized by the impact research community that really should be there. This 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. It has been argued that megafauna extinctions already set in in North America before the Younger Dryas, during the Bølling-Allerød warm climatic oscillations (e.g. Gill et al. 2009, Science 326, 1100-1103). Likewise, elsewhere in the world Late Pleistocene megafauna extinctions were not a punctuated event either.
Rancholabrean fauna (Illustration credit) 
The same goes for the archaeological side of the story: is the end of Clovis really a punctuated event at 12.9 ka? And if it is, does this point to extinction, rather than cultural change? In other words, is there really evidence of a dramatic demographic break/discontinuity at the Younger Dryas boundary, archaeologically? Where Clovis is concerned, it should be taken into account that evidence suggest that the appearance of Clovis was rather rapid as well (Waters and Stafford 2007, Science 315, 1126). With a rather sudden onset, a rather sudden end seems less odd.
Credit: National Geographic
Clovis could be a response to the shortlived, warm Allerød climate oscillation, explaining both the rapid onset and disappearance without the need to invoke an impact at the start of the Younger Dryas.  We should realize that what we call Clovis is a techno-typological concept only, not a demographic entity. The end of Clovis does not necessarily equal the end of human occupation of N-America (note: I am not a N-American paleoindian archaeologist, so I have no vested opinion on these questions and refrain from definite judgement on how "sudden" the end of Clovis was, and matters of demographic continuity following Clovis. Others are more qualified to judge these issues). 
 That the Younger Dryas (certainly in conjunction with the preceding unusually warm and moist Bølling-Allerød warm climatic oscillations) represents a clear and severe climatological fluctuation, enough to potentially disrupt human presence, is beyond doubt. The central issue is therefore the cause, so even if there was a break in human presence, that does not prove a cosmic impact itself, as there are alternatives to explain the onset of the Younger Dryas. Notably, the effects of an influx of fresh meltwater from the Laurentide icesheets on the Oceanic thermohaline circulation (see for example Broecker 2006, Science 312, 1146). It therefore really boils down to the question whether there really is good, acceptable evidence for a cosmic impact, other than the faunal extinctions and archaeological change happening near (note the near) the Younger Dryas.
The absence of any clear impact crater or other impact markers dating to the YD does present a problem in this regard. With an event of the proposed size (4-5 km body impacting), and this young an age, impact marks should be visible. Impact in the ice sheet going "unnoticed" is not a viable explanation. That argument does not seem to appreciate the size of the event necessary to create extinction on a continental scale. An object large enough to have such consequences would penetrate through the ice sheet and excavate a crater in the bedrock below the ice: we are talking about craters with a diameter of 50 km or more and a depth of 10 or more kilometers here (see Hills & Goda 1993, Astronomical Journal 105, 1114). An air-burst (a fragile, e.g. carbonaceous or cometary cosmic body exploding and annihilating in mid-air) does not really explain the absence of physical impact evidence either. With an airburst of this magnitude, one would expect geologically traceable results, such as the presence of glassy melt-sheets (impact melt glasses), deposition of meteoritic evaporation products, massive blast damage and other geologically visible traces under the airburst location and a wide area around it.
Radar: Incoming! 
Hawkeye: Radar I don't hear anything. 
Radar: Wait for it... (Photo credit)
 As Melott et al. recently pointed out, an impact this size should leave a notable marker in the Greenland ice cap in terms of (a.o.) enhanced nitrate concentrations. While some nitrate enhancements were indeed presented as evidence by the original YD impact hypothesis authors, the signal that is present in Greenland ice core data however falls well short of what an impact of this size should create (Melott et al. 2010, Geology 38, 355-358). The small signal that is there points to forest fires during the YD, which however can have all kinds of causes (for example, climate change and ecological change, e.g. in the herbivore community, creating an environment more susceptible to forest fire as a results of the wild climate oscillations at the Allerød-Bølling-Younger Dryas interface).
Likewise a reported "Iridium enhancement" at YD levels (Firestone et al. 2007), is not corroborated by other researchers looking for it, including the same sites (and even the same sediment samples) that Firestone, West et al. sampled (Paquay et al. 2009, PNAS 106, 21505; Haynes et al. 2010, PNAS 107, 4010). Paquay et al. also found no trace of other geochemical impact markers that should be there, for example in the 187Os/188Os isotopic ratios of YD sediments (introduction into the atmosphere of extra-terrestrial materials from the impactor should off-set these Osmium ratios. There is no evidence for such an off-set: 187Os/188Os isotopic ratios of YD sediments are completely terrestrial).
The YD impact hypothesis proponents have claimed elevated, concentrated levels of magnetic and carbon spherules in YD sediments (Firestone et al. 2007). Several researchers have however again failed to replicate these observations (including on the very same sampling localities as those of Firestone, West  et al.) and point out that what number of metallic spherules are present in these sediments, is consistent with the natural annual background influx of such micro-meteoroid materials and that presence of these is not restricted to the YD levels (Surovell et al. 2009, PNAS 106, 18155; Haynes et al. 2010, PNAS 107, 4010). I can attest myself that you can find metallic spherules in any archaeological sediment, if you look for them (I found them in Holstein age sediments from Schöningen for example), and geologists have been recovering spherules from geological deposits of widely varying ages for years already. Others have pointed out that the carbon spherules need not be of cosmic origin at all (they can be fungal in origin, or even be insect coprolites) and indeed Scott et al. (2010, Geophys. Research Letters 37, L14302)) feel the reported carbon spherules are consistent with a biological origin, rather than impact-generated.
The "novelty" impact markers proposed are heavily disputed as well. For example, the "nanodiamonds" that feature heavily as evidence in the discussion (Kennett et al. 2009, Science 323, 94), might not be nanodiamonds but graphene (which is present in non-YD sediments as well) according to Dalton et al. (2010, PNAS 107, 16043). Dalton et al. did not find any true nanodiamonds in YD age deposits. The distinct lack of other meteorite-produced impact elements together with these "nanodiamonds" remains a problem as well for the interpretation of these "nanodiamonds" as impact markers. It should be noted that nanodiamonds were never considered to be clear impact markers (although it should be noted that nanodiamonds do occur in some meteorites, notably in Ureilites [see below], and can form in carbon-rich impact target rock due to shock pressure) before these were presented as such by the YD impact proponents.
A meteorite that does contain nanodiamonds: a small fragment of the NWA 2625 meteorite, an Ureilite found in the Sahara in 2004 (collection M. Langbroek).
It gets even more dubious, when it concerns some of the very first evidence presented for the YD impact hypothesis. These consisted of what was claimed to be microscopic impact damage on flint tools, plus what were claimed to be small metallic meteoritic fragments embedded in some mammoth tusks and megafauna bones. Radiometric dates on these tusks and bones however have shown that they do not date to the Younger Dryas at all, but have various ages (up to 10,000 years older than the YD – for a review, see Pinter et al. (2011, Earth Science Reviews 106, 247-264). The "microscopic damage" on flint tools is highly dubious (and downright pseudo-science in my opinion): such small meteoric particles as were proposed to have inflicted this damage, should not retain cosmic velocities and as a result would impact with such low velocities that they could not have created the claimed damage on hard flint surfaces (see also Pinter et al. 2011, Earth Science Reviews 106, 247-264, who remark the same).
Similarly dubious are the claims for notably elevated radioactivity levels in YD faunal bones and elevated U and Th levels in YD sediments (Firestone et al. 2007). Radioactivity has never been associated with cosmic impact before. The natural radioactivity of meteorites is considerably lower than that of the average terrestrial rock and mostly due to shortlived cosmogenic isotopes created by cosmic irradiation in space, i.e. isotopes that should have completely decayed after 12,900 years. Radioactive meteorites (or comets) belong to the realm of comic books and bad Hollywood movies, not science. Again, this part of the hypothesis heavily smacks of pseudo-science. Moreover, these findings could again not be reproduced by other researchers (Haynes et al. 2010, PNAS 107, 4010).
As the reader will have noted, there is a string of "non-reproduceable observations" involved by now. That is ominous. It points out that much of the hypothesis is on very shaky grounds. Add to this the string of negative observations of established impact markers that should be there, but are not, plus the decidely odd "observations" such as claimed elevated radioactivity levels that have hitherto never been associated with cosmic impact (and again, cannot be reproduced by other researchers).
Taken all together, it doesn't add up.
To summarize: widely established impact markers that should be there are either not observed at all, or when initially reported by Firestone et al. turn out to be non-reproducable observations when other researchers investigate what in several occasions are the same deposits (and sometimes even the same samples). The "novelty" impact markers presented by Firestone et al. are not only unusual but also highly contentious, with "nanodiamonds" that might not be nanodiamonds and iron-particle peppered mammoth tusks that turn out to be from widely varying ages instead of dating to the Younger Dryas. In addition, paleontologists dispute that a worldwide or even regional punctuated extinction event happened 12,900 ka ago (pointing out that extinctions were already in progress before that date in North America), and evidence for a clear demographic break in human presence in North America at this moment in time is ambiguous as well.
This leaves virtually no firm evidence for either:
(a) the occurrence of an impact at 12,900 ka, or
(b) the "punctuated" phenomena at 12,900 ka purported to be explained by this impact hypothesis itself.
After Alvarez et al.'s famous 1980 Science paper on cosmic impact as a cause for the K-T extinction event (including the dinosaur extinction), impacts have entered the scientific main stream as a recognized force in the geological and biological history of our planet. As a personal opinion, I feel the YD impact hypothesis is an example of how cosmic impact in the wake of this rising acceptance is now used and abused as a "deus ex machinae" by some, to explain all that seems remotely unusual in the geological, climatological and archaeological record.
That is however not the way cosmic impact hypothesis should be evoked, and it detracts from cases where well-documented cosmic impacts were truly occurring and possibly meddling with human presence. For it is a fact, that large cosmic impacts did occur solidly within the timespan of human evolution. The formation of the Australasian tektite strewnfield 0.8 Ma ago in SE Asia for example is a genuine, well-accepted, large cosmic impact event on the global effects threshold--and Homo erectus was already plodding through Asia at that time (see appendix to M. Langbroek 2004, Out of Africa, a study into the earliest occupation of the Old World. BAR Int. series 1244, Archaeopress, Oxford).
Like Rob Gargett, I however smell that "this one isn't going away for a while". Perceived cosmic armageddon at the eve of human occupation of the Americas is too spectacular to be dropped easily.
Marco Langbroek, April 10, 2012
Institute for Geo- & Bioarchaeology (IGBA)
Faculty of Earth and Life Sciences
VU University Amsterdam
De Boelelaan 1085
1081 HV Amsterdam, the Netherlands

twitter: @Marco_Langbroek;;;

I'm sure that Dr. Langbroek would welcome your comments. [clears throat] Fire away!