Tuesday, April 07, 2009

The KT Extinction: The Day the Sky Fell

An Introduction

I have thought a lot about what I was going to write while my family is away seeing my in-laws. I had originally planned to write about climate change in different places (it's partially done and may get finished before La Kidda and the spouse return, but it might not) and I had planned on writing about the therocephalians as well. However, Zach drop nuked an ubersized paper on the gorgonopsid skull functionality and I've been madly trying to get more funding, bending metal, and getting set to fly or crash The Wind at Dawn for for Team Phoenicia - I just wanna fly! Really! So the thero post is dumped for the time being. Instead, I realized that I had let my mass extinction posts be neglected. It has been more than a year since I wrote about YAGUMETs and Stop Dreaming (the comparison of the KT to the PT Extinctions). I had promised a post on the KT Extinction. While in some ways Stop Dreaming was that post, that it was a case of trying to disprove the hypothesis that the KT Event was caused by the Deccan Traps. This post is intended to be the opposite: to set out the evidence on what caused the KT, ie a proof.

Time's Echoing Archosaural Roar

The dinosaurs. They have fascinated us to the extreme for since their discovery. They have evolved in our mental space from the great lumbering, stupid giants to the fast and terrifying semi-birds of today. Always, always, we have wondered: what killed them? They are so huge and powerful, even when they were the stupid version, why in the word did the mammals of today even stand a chance against them? The biggest of ours is far, far smaller than the greatest of theirs...sooo...what happened? Why are they as 'dead as the dinosaurs?'

There have been a lot of theories over time as what caused the demise of the dinosaurs. They are of varying quality and testability. Sometimes they held out far, far longer than they ought to have in a serious scientific discourse. However, almost all of them had a major problem when people first asked the question of what killed the terrible lizards: whatever theory it was, it had to be compatible with Uniformitarianism. Otherwise, the hypothesis would be supportive of the discredited and heretical Catastrophism. I won't recap the intellectual war between Cuvier and Lyell - every. single. book. on the KT or most mass extinctions does this in such detail that I now skip those chapters. Interesting the first few times, irrelevant after a while. I will summarize to say that in the end, in the last 30 years, a variant on the catastrophist position has won out: mass extinctions are the epitome of that POV. However, the ideas about what killed the dinosaurs were once compatible with uniformitarianism. Let's look at the goofy things.

Discredited Silliness & A Mistaken Belief

There are really two goofy theories and one that just didn't pan out even though it had some basis. The other two are just so goofy though in retrospect that you have to wonder how they could survive to the modern times themselves. However, quite often, they do appear once again and sometimes backed by the most surprising of people.

The first silly idea that I am going to touch on is that a virulent pathogen wiped out all the dinosaurs. That the pathogen spread throughout the world of the Late Cretaceous and wiped out everything us just plain ludicrous. There is no evidence that there was suddenly an increased amount of sick dinos based on their skeletons. There really ought to be. Even so, it ought to be noted, fifty percent, 50%!!! of all mammals and birds got wiped out too! There are exceedingly few crazy lethal pathogens that match this and almost none would wipe out both mammals and birds and nonavian dinosaurs on this scale. Furthermore, this crazy pathogen would have had to been able to knock out molluscs too: like say, the ammonites. I have a hard time believing that anyone took this one very seriously. The 'nice' thing about this hypothesis was that it didn't disturb the geological present is an excellent guide to the past meme, since plagues were well known in Europe and they leave little trace geologically. However, it is completely wrong.

The second silly idea is an outgrowth of the misunderstanding of how evolution works and its misapplication to the social sciences. There were some very embarrassing and stupid ideas that would come of the misapplication and misunderstanding of evolution, social darwinism, frex, but another was that evolution is about constant improvement and that in turn led to the belief in mammalian superiority. Yes, supposedly, we mammals are the biggest, meanest, most advanced and nastiest thing this planet has ever evolved and only something that replaces us will be superior. The way that this was exhibited with respect to the dinosaurs was that the little fuzzy mammals were supposed to have eaten the eggs of the dinos and that caused the extinction. The only problem is that the mammals lived alongside the endothermic archosaurs for around 100 million years before the dinosaurs went and extinct. When presented with that fact, it has been countered that it was really the placentals that were superior and they ate the dinosaurs' eggs and outcompeted the other mammalian varieties. Also ludicrous, the placentals didn't outcompete anyone at least until the end of the Eocene and they are only now giving the marsupials of Australia any problems despite having been present in rodent form since the Miocene. (psst, the paleogene megafauna may not have been placental. Pass it on.)

The last incorrect theory shouldn't really be called silly. There was some evidence for this to a degree and that evidence was simply misinterpreted. However, this one, too, did not disturb that Uniformitarian view of geology. This would be that the world's climate simply changed and that the dinosaurs died out. There is some support for change in the world's climate. There used to be a great mucking sea up the middle of North America for example. However, it receded as the Atlantic basin widened and deepened. When this happened, climate around the inland sea changed from coastal tropical to being drier and more seasonal. The diversity of dinosaurs decreased. This was interpreted as a decline in the dinosaurs in general. However, there were two oopses here. The first is that more arid conditions naturally support less diversity and what diversity that it does support tends to be less of the megafauna variety. Secondly, it ought to be noted in the regions where the climate was the same there was no loss in diversity at all. The dinosaurs weren't really declining. The sites we were getting the fossils from just happened to have different environments at them over time.

The Last Two Standing

There are two more theories that were left. One wasn't even considered until a later to be UC Berkeley geologist and his famous father stirred the paleontological pot. That would be the idea that the dinosaurs were killed by a bollide impacting with the world. The second theory was as much a reaction to the first: that vulcanism was actual cause. Both sides produced some personalities that have been central to the fight between them such as Jan Smit and Gerta Keller, Walter Alvarez and Vincent Courtillot, and, of course, Luis Alvarez (a colabbie, no less). The debate has had the heat and blinding flashes of bollide impacts and massive volcanic explosions and, in fact, I am surprised that the a fore sentence with those individuals listed didn't burst into flame being listed side by side. To read the calmest of the writings on the subject I recommend Courtillot's Evolutionary Catastrophes and Alvarez the Younger's T Rex and the Crater of Doom. The struggle has been very, very bitter and more than a few friendships have been lost over it.

As interesting as the human dimension on the subject is it has been covered in extensive detail. I really want to discuss why the KT Extinction was caused by the Chicxulub impact and the evidence for it. I do want to note before I move on that with the evidence from the KT Extinction debate and the evidence of other lesser known geological events like the Channeled Scablands have overturned the idea of Uniformitarianism to be replaced with a neocatastrophist point of view.

Those that pushed forward the vulcanist stance that the Deccan Traps were the cause of the KT Extinction. Their argument has been that the Deccan Traps are located at the right time to cause the extinction and since there is an interesting correlation between flood basalts and mass extinctions that it must be the culprit. They have systematically attacked the evidence for a bollide impact being the cause of the extinction, especially Chicxulub. One thing that I have not read by them is why the Deccan Traps caused the extinction. What evidence is there that their hypothesis is correct? The problem is, other than the timing, the evidence does not stack up well for the Deccan Traps: the KT Extinction had a fundamentally different signature than the one mass extinction generally accepted as being caused by vulcanism. You can read about the differences here in my Stop Dreaming post.

There was one more damning bit of evidence against the Deccan Traps causing the KT Extinctions that I mentioned in passing in the comments of that post, but not in the body (out of time as I stated). The Deccan Traps are flood basalts, to be sure, and big ones. However, there is evidence of cessation of the eruptions and between the layers of basalt there are sedimentary sections. In those sections are fossils of dinosaurs. The different sections have the same dinosaurs. The Deccan Traps didn't even wipe out the indigenous dinosaurs of the island continent of India. (cite coming, promise)

That would leave the impact at Chicxulub as the protagonist of the post. Is there evidence for the impact and its Crater of Doom causing the extinction? Is there a good mechanism for the extinction? Is there a general understanding of what happened? Yes, there is.

The Last Man Standing

It was freezing and cold. The triceratops moving with increasing difficulty. There was little energy left in her. She couldn't see a thing and she was the last of her herd. It was pitch black and she couldn't see a thing. She was no night herbivore. She was in constant terror. It wouldn't matter soon unless she could find food. She was about to expire. She was simply too huge to live off the meager, frozen bits of vegetation she had been finding. The irony was that her size had saved her, when the cold blackness came. The hatchlings and smaller members of the herd had expired first. Then the largest. Then the others until she was all that was left. She found water and collapsed in it. As the world, such as it was, faded away, she heard something. Squeeking. Her life would be the payment for others.

When the bollide came crashing down 65 million years ago, there were multiple ways that the blast and its after effects killed. There were ways that were originally conjectured that it definitely did not kill with though. The bollide that hit had an estimated diameter of 10 km derived from the massive size of the Chicxulub Crater. Oh, the reason that I keep saying bollide is because we don't know if it was a asteroid (mostly stony thing) or a comet. However, in 2007, there was a report that astronomers had found the alleged source of the
Chicxulub bolide. A much larger carbonaceous chordite, a rare carbon and volatile stuffed variant, asteroid broke up and one of the pieces impacted on the Yucatan Peninsula 65 million years ago.

We are going to make some assumptions here. If you read this, consider a step up from back of envelope calculations. Not much more. I'd consider actually doing a simulation on the machines at work, but time wise, I'm swamped. Just getting this post done has taken me weeks. For the effects of the impact, we'll assume that half the energy of the impact was translated into thermal energy and the other half into blast effects. This is overly simplistic, but will do for our purposes. Our carbonaceous chordite 10 km bolide has just blasted a 300 km crater into the ground.

The immediate effects would be the blast itself. The impact had the power of ten thousand times the sum of the nuclear arsenals of the world at the height of the cold war. Going by the Effects of Nuclear Weapons, a volume that has been used extensively to try to model the effects of such a large impact on the world.

The shock waves from that impact would have been tremendous and absolutely devastating for life. Everything from the Yucatan to the approximately Thompson, Manitoba, Canada would have been killed just by the shockwave to the north, to the Columbian-Brazilian border in the South (remember, South America was further south back then), and way out into the Atlantic and Pacific. This is just the shockwave. This is only one of many effects that would have been devastating to the End Cretaceous ecosystem.

There would have been a massive tidal wave to go along with the this shockwave. The nearest equivalent in recent human history was the tidal wave that was produced by the 1960 Valdivia Earthquake (or Great Chilean Quake) that produced a tidal wave that hit the Hawaii with wave heights exceeding 35 feet (10.5 meters) 5,000 miles (8,000 km) away. Keep in mind that the Valdivia Quake was a 9.0. The impact would have been the equivalent of an 11+ on the same scale. Tidal waves would have lashed the whole of the exposed Atlantic Basin and even the southern Pacific far, far more than the relatively "minor"disturbance of Valdivia. There may well have been the equivalent of Lituya Bay waves cashing into Europe, Africa, and possibly even Antarctica and Australia. We already know that many of the nonvian dinosaurs favoured the lowlands in the Late Cretaceous. For large swathes of them, even outside of the killing range of the shockwave, the megatsunamai would have been just as great if not greater of a killer.

These alone would have been devastating to the Late Cretaceous terrestrial ecosystems within the killing distances of the impact's tsunamis and shockwave.
These are not the only killing mechanisms, if they are a little more of what people can grasp since they have some tie into our collective experience. However, there's a whole lot more that happened. One of the best bits of evidence that proved there was an impact in the Yucatan was yet another killer: the tektites.

What is a tektite? It is not a murderous lost Mesoamerican civilization, though the placement of the impact teases like it could be. It is a very small, spherical piece of rock that was heated to insane temperatures. When an impact takes place, it vaporizes gigatons of rock. Some of this is ejected from the Earth. The vast majority of it comes back down, coalescing as spheres of still really hot rock, glass really, that falls back to Earth. This in turn causes fires to start. These tektites have been found around the world with an ever increasing number closer to the Yucatan. This rain of red hot dust around the world would have started a global conflaguration of varied degrees. More closer to the impact. Less further away. Besides the direct death dealt out by the local fires, the most devastating bit would have been the smoke. Smoke everywhere in the world. Note: there was some question whether or not the conflaguration took place: it appears that it did.

This smoke would have joined the dust, gigatons and more, kicked up into the atmosphere by the impact. Furthermore, the Yucatan even back in the Cretaceous, held vast stores of oil. This too would have been vaporized and burned. The dust, the burning oil, the burning vegatation, all in turn would have blocked the light from the sun. This killed far, far more than the "pathetic" direct effects of blast. The temperatures would have plummeted, everywhere, around the world, snapping down to modern day arctic winter conditions for months on end, even in the tropics, and possibly up to a year. That would have killed even the largest tropical megafauna and most, but not all of Cretaceous fauna was ill equipped for dealing with the cold snap. This would have been really bad news for the terrestrial plants and animals. Trees would have died. Forests die. Vast areas of land plants just die. With nothing to eat, the herbivores follow. With the herbivores gone, the carnivores follow. the megafauna is 100% toast. Even the smaller sized animals die in droves: 50% of all Cretaceous mammals were wiped out too. No place on earth would have been untouched by this.

What of the oceans though? The reefs would have been crushed by the tsunamis, but even then there would have been enough plaktonic larva to reestablish reefs PDQ. However, even if the reefs were shielded or completely out of the way of the tsunamis, there was no escaping that crushing darkness. The blocked sunlight would have crushed the photic zone plakton. Anything that depended on the plakton was toast. Anything that produced larva that lived in that plakton was toast. Antyhing that depended on anything that ate the above was toasted. Based on the study of teleost fish at the KT Boundary, this has been born out. In fact, it seems that the KT extinction killed vast amounts of everything in the photic zone. The larger you were, the more the sucky it was.

What Didn't Happen

One of the big suggestions that bloomed out of the arguments over the KT Extinction was the suggestion that vast amounts of acid rain poured out of the skies. There is zilch evidence for it. In fact, the very ecosystems that ought to have been impacted the most - the brown water ecosystems of the freshwater realm - were some of the least impacted by the extinction event. One of the most sensitive class of terrestrial vertebrates that ought to have been absolutely mopped by the introduction of massive amounts of acid rain were no more effected than any other class: whom do I speak of? Lissamphibia. They weathered the KT as well as anyone. If there had been extreme amounts of acid rain, they'd not have survived probably at all!

The Evidence

Now that I have described how the Mesozoic ended, the obvious retort is, what evidence is there for this scenario? This has been a fanciful tale, but....what sort of data bits do you have to support it? There is alot. Now, as I said, I've already written the negation of the Deccan Traps as the trigger mechanism of the KT/K-Pg Extinction. Now what do I have to support the contention? There's a lot. Honestly, this is about as clinched as they go for mass extinctions.

First off, the Yucatan has this massive crater that matches the geochronology of the KT Extinction. Known at the Chicxulub Crater, it has a massive diameter of over 300 km and the inner crater ring is 180 km. The dating of the crater is pretty rock solid, if you will forgive the expression, but it is the one of the areas where the vulcanists attempt to erode the strength if the impactists' position.

Connected to this is the famous iridium layer. This is world wide at the the KT Boundary. It is what tipped Walter Alvarez et al off to their discovery and has since been verified over time and again. The iridium is almost certainly extraterrestrial in origin. There has never been a single volcanic event that caused the world spanning iridium deposits ever.

As already mentioned, the tektites have been found world wide and these have been centered on the Yucatan. The closer you get to the Yucatan, the more tektites are found. The distribution pattern completely matches the Chicxulub Crater being their source.

Furthermore, there's the shocked quartz. Quartz when subjected to obscene pressures will deform and crack in a manner that is consistant with a the pressure being exerted in an extreme form from a singular source. So far, shocked quartz has been found related to nuclear weapons tests and impact events. There has been little to no evidence at all that this comes from volcanic events. The KT/K-Pg Boundary is rife with it and the distribution again indicates that the source is the Chicxulub Crater.

So far, I have shown that the KT and Chicxulub Impact have been geochronologically synchronous. That's not enough. I have to show that there is evidence of the predicted effects. Now let's go there.

For the impact shockwave, there's very little evidence, to be honest. However, indirectly, there's the fern spike. Ferns, as I noted in my carboniferous ecology post, are the phytocaste dedicated to disaster expoitation. The whole of North America and even other parts of the world, including remote portions such as New Zealand, the fern spike is recorded. It's also of very limited geochronological extent: once the other phytocastes recovered, the ferns' spores faded into the background in the pollen. This indicates something devastating happened and happened fast. The ferns, being specialists at exploiting catastrophies, zipped in and then faded away.

For the tidal wave, there have been deposits found in Mexico and Haiti that match the predicted flotsam and extremely disturbed sediment. This has been disputed by Keller et al, but so far as I can tell, only by her. This has been supported by Smit at el and the feel I get is that this will not be settled completely until after the passing of this generation of paleontologists. Some of the worst ad hominem attacks both ways have come out of the study of the tidal wave deposits. To clinch the Chixculub megatsunami, deposits outside of these need to be found. If I were looking, I'd go to North Africa, northern South America and, possibly, Ausralia or Antarctica's appropriate northern coast.

As for the evidence of the global conflagration, carbon lumps have been found. Additionally, a recent paper came out and stated that there is extensive geochemical evidence that combustion was taking place all over the world from different deposits. If this holds up, this would be yet another hard clinch on the world ending event that the KT Boundary transition was.

Finally, there's the very nature of the extnction event. I talked about that in Stop Dreaming. The photic zone in the oceans were devastated while the benthic were largely untouched. The terrestrial realms were completely upended. 50% of the angiosperms in North America went extinct on the boundary. The fern spike, as noted, was global.

An Item That Needs to be Addressed

The first is that there can not be a single cause for this extinction and any other. Please read both "Addressing YAGUMETs" and Stop Dreaming. If you want to show two extinctions have a common cause, please compare the patterns of the extinctions. They need to be similar in the biomes they impact, the nature of the creatures being impacted, and evidenciary nature. If they do not match, they are not caused by the same thing. Sorry. Shoehorning didn't work for the ugly step sisters and it won't here either.

The KT Extinction was different from the Permian Extinction. The Permian was similar to the Late Triassic Extinctions. Several "minor" mass extinctions match too. None of the previous were similar to the Ordovician. It's unknown which the Devonian matches, if any. The 6th Mass Extinction doesn't fit any of the previous extinctions. That will be the next mass extinction post, but not yet. There is no Grand Unified Mass Extinction Theory. Deal.

In The End...

When the Cretaceous ended, 50% of all genera were extinct. 17% of all animal families were wiped out. 50% of all angiosperms in North America alone went extinct. All of the dinosaurs save the birds were extinct. The great marine reptiles were gone. The pterosaurs were toast. The majority of the archosaurs and most diapsid megafauna was swept away. The archosaur grip on the ecologies that had lasted for over 135 million years, and arguably even 150 million years, was ended. The therapsids, namely the mammals in our different stripes, were once again given the chance to dominate the ecologies. This time we did and we snapped back rather well. In fact, very, very quickly we diversified, but it'd not be for a few million years that we had a lot of megafauna.

In the end, the dominance of the megafauna by the mammals, by chance, produced us. The first genus to contemplate itself. The first genus to be a WMD. The first genus to produce a mass extinction all by its lonesome. That, however, is a post for another time.

And, yes, for those that are wondering, this was a much needed paleo break from the Team Phoenicia work. Hopefully, I didn't do any egregious sins mathematically or otherwise here. I'm a little distracted and will go back to fix anything missed. The next paleo post will be why the methane calthrate hypothesis for the PT Extinction by its lonesome is an epic fail: hint, the PETM.


Bec said...

What a brilliant read. Thanks so much for this.

Will Baird said...

I am glad that someone liked it. I got more responses on my other mass extinction posts! Then again, this one has been done to death, really.

Anonymous said...

Anonymus99 4/16/09

Will, you have summarized the current beliefs about the K-T extinction in great detail and for that you should be commended.

However, the last man standing is a straw man....bolide impact did not cause the extictions. I can't address every issue raised, but here are a few:

1. The belief that mammals remained at shrew-size during the reign of the dinosaurs is false. Some became the size of dogs or wolves and preyed upon dinos..... not just egg eaters.

2. There was a decline in dinosaur diversity (at least in N. America) where triceratops and tyranosaurs are almost always depicted as the last dominant species. Stegosaurs, most sauropods and other large dinosaurs were long gone by the time K-T came. It is conceivable that there were a lot of small, similar dinosaurs but this is diversity in a narrow band.

3. If the bolide impact had the effect suggested, where is the bone pile? We can't sweep this away with the Signor-Lipps effect.

4. If post-impact effects were like "modern day arctic conditions" how did honey bees, birds, lizards, snakes......survive? Tropical and sub-tropical conditions existed prior to K-T and the birds then were probably comparable to today's tropical birds.....and could not surive the cold snap you suggest....nor the honey bees and the flowers they needed to survive.
Why didn't the polar dinosaurs survive?
There are just too many issues that make "the last man standing' a straw man.


Anonymous said...

first of all, those animals were animals that evoled,second, Chicxulub rules