Impact that killed the dinosaurs?

[Brian G Turner]

Here is an article from the BBC about the recent NASA mappings in the area of the Chicxulub crater.

AND this is the perfect excuse to get onto a topic to get my teeth into.

First of all, the entire notion that the Dinosaurs were wiped out by the sole cause of an extra-terrestrial impact, is so utterly flawed I am astonished it's received such general acceptance.

There may be a K-T boudary in very late Cretacean rocks, but all this signifies is that an impact took place. Studies of the flora suggest the extinction taking place over millions of years (in fact, as the peak in a long-running tradition of extinctions throughout the Cretaceous period itself.

Not only that, but the clincher is that by admission of the "pro"group itself, the body in question responsible for the Chicxulub crater could not have had the required energy to cause a mass extinction! So, they claim there must be a hitherto unknown "threshold" level, where smaller impact destruction suddenly takes on a much greater magnitude. But there is no evidence for this!

The bottom line is two things:

1/ North America was hit and damaged - therefoer the rest of the world must have been, too

2/ People want to hold on to sole causes where there are none!

There's no doubting that the Chicxulub impact would have had fairly serious repurcussions on the global environment. But it really has to be considered in light of other palaeontological evidence - all of which suggests a gradual demise over 5 million years or so.

And there's also the other important apolalyptic event of the time - the Deccan traps of India tally at around 65 million years of age. Possibly linked to a disturbance of the Earth's mantle by the impact - but probably not as the impact simply did not have as great an impact energy as is being claimed (through the "threshold" argument).

So why are the public being fed this apocalyptic asteroid/comet theory?

And, more so, why are scientistis disregarding geological evidence in the first place to sustain such an argument?


There. Rant over.

 

[Survivor]

Well, as for why it is popular, environmentalists and anti-nuke activists really liked the idea.

But that doesn't mean the theory has no merit. In a top heavy ecosystem (like any ecosystem that has dinosaurs in it) a relatively small global event--or even a hemispheric event--could easily cause a domino effect. Just because our modern ecology appears to be far more robust doesn't mean that that single event couldn't start a chain reaction in a global ecology that supported dinosaurs.

And I think you're getting carried away when you characterize the Chicxulub event as not being large enough anyway. It was a serious impact. Maybe not large enough to directly kill animals all over the planet, but then, no one is suggesting that. The bottom line is that it appears to have been the most significant destabizing impact.

As for that 5 million year long extinction period, http://news.bbc.co.uk/1/hi/sci/tech/1209870.stm suggested that the K-T boundry is nowhere near that time span. I'm thinking that some of your conclusions are unusual enough to require at least a little more explaination.

 

[Brian G Turner]

This following statement from this article from New Scientist about possible future asteroid collisions, pretty much sums up the entire issue of the Dinosaur extinction:

"Virtually everyone agrees that the asteroid that hit Chicxulub in Mexico 65 million years ago killed the dinosaurs, but how it did so is unclear. A long-standing theory is that clouds of dust hung in the upper atmosphere for months, blocking sunlight and stopping plants growing. But no one is sure that this is really the reason..."

The logic here is astounding - the statement basically states that "here is a theory that no one understand but everyone should agree on".

This statement is obviously at odds with the classic general scenario, detailed here in an earlier report.

The main contention is not simply that the asteroid event is being heralded as a sole cause for the extinction of the Dinosaurs - but also, the pro-asteroid camp itself has declared that calculations show that there could not the be energy required to cause a global catastrophe. (Sorry - I know this was mentioned in New Scientist articles, but those are not available online.)

As for the idea of a cascading global phenomena - generally it's the cause of which is the actual cause of dissension. For example, asteroid impact, or Deccan Traps vulcanism? Yet are generally already assumed to support the notion of a sole cause asteroid impact within mainstream science.

The problem I suspect is that the issue has become deeply politicised - there is contrary evidence on both sides of the fence and in each theoretical camp. I also strongly suspect that the impact theory is being promoted in majority by US researchers - anything that affected the USA must also have had an equal impact on the rest of the world! This is almost astonishingly suggested here, where a single dig in Hell's Creek, which suggests flourishing life on the North American continent until 65 mya, therefore means extrapolates to mean that the entire world was therefore subject to the local variations of local North American flora and fauna!

You mentioned the article on the leaves record - but that merely records rising CO2 rising - and does nothing to support the idea of a impact unless an impact has already been accepted as being the true scenario!

A more general look at the issue, such as in this article shows some of the contention of the entire arena. Look at the article carefully and the argues used by the pro-impact group are very picky, compared with the general evidence of the period being presented.


Also note how the atmosphere over the extinction of Dinosauria differs from the great Permian Extinction of 250 mya. Because of the current posturing over the impact theory for 65 mya, therefore the Permian Extinction must follow the same modus operandi - yet this really isn't being supported at all, as described here and here.


Generally...

The problem here is more likely that the debate has settled too far into "either/or", and the notion of "single cause theory", which is dangerously close to oversimplification.

The actual global evidence, so far as I can see it, is localised disturbance to North America by the Chicxulub impact, but a general trend of extinctions already occurring. What this cause is no one seems to know, but it does appear that the Deccan Traps event greatly accelerated the issue - an issue already in occurrence.

The idea of "either/or" is just insupportable, but that s precisely what is being touted as the accepted position by mainstream science - in favour of the impact theory, of course.

What's sad here is that other possibilities offer themselves, but are ignored because they do not fall directly into the "either/or" camp. For example, what about the theory that the Deccan Traps eruption occurred due to a large impact on that site? Maybe I've already argued against it, but it would present a far smaller mechanical problem in terms of an extinction scenario, especially with reference to articles such as this which expressly addresses the notion of impacts puncturing the earth's crust (and especially reference this with the notion of the vulcanism associated with the Permian Extinction, as above). There's also the notion (again, sorry, not available online) of the earth's crust being shocked by impacts, and that an impact at Chicxulub may have been enough to cause the Deccan Traps event.


Anyway - that's a mighty long-winded looking post, so I'll leave it there. I'll finish with reference to two other online articles - this one here has a nice generally neutral appraisal, with further links to specific topics, whilst the website of Dewey McClean, who postulated the Deccan Traps event as an extinction trigger, can be found here.

 

[Survivor]

Okay, first off, let's get one thing straight. Vulcanism on the scale of the Deccan flows cannot have been directly caused by an impact. They were the result of activity in the Earth's mantle, and an impact big enough to have initiated that activity would have destroyed nearly all multi-cellular life forms on Earth. There is no evidence for an impact on that scale in the fossile record either.

The exact mechanisms of mass extinction due to a large impact are unknown because we have never been able to study an impact of that size on the Earth. The iridium rich layer in the K-T boundry covers all the continents on Earth, though, so this was not a local event to Central America (even if it were, all the land masses were closer together back then). It strongly suggests that the locally catastrophic event was followed by global reduction in insolation, which would have adversely affected plant populations world-wide (this would have greatly contributed to increases in carbon dioxide levels, but vulcanism remains a strong influence there). We don't know exactly how much dust was injected into the upper atmosphere, exactly how long it was up there, exactly how much it reduced insolation, but we do know that it was a global event.

Your rejection of the Hell's Creek evidence is a silly prejudice. Europe, Asia, and North America were all a single landmass with a high degree of climatic similarity 65 million years ago. The Hell Creek Formation was selected because of its geology, not because "anything that affected the USA must also have had an equal impact on the rest of the world!"

It has been theorized that possibly the 10 kilometer object that created the Chicxulub crater may have been only a fragment of a larger object that broke apart and struck several places. I see no reason that this is impossible, or even unlikely. It has also been posited that the mass extinction was made worse by other factors, like the Deccan vulcanism. I think that this is nearly certain. But the fact remains that the available evidence supports a fairly sudden global mass extinction of 70% of the species known to have existed at that time, and an impact as being the primary cause of that extinction. There are competing theories but none of them have the same degree of evidence or argument supporting them.

There was an impact, and it did have a significant global impact. The physical evidence is very clear on this point. No other competing theory has as strong a claim. That doesn't mean that work on elucidating what else was going on is pointless. Quite the opposite. But it is bad science to claim that because work is being done on the Deccan flows or the evolution of flowers or weakening of the Earth's magnetosphere, this somehow invalidates the evidence presented in favor of an impact.

You say,
[glow=red,2,300]The idea of "either/or" is just insupportable, but that s precisely what is being touted as the accepted position by mainstream science - in favour of the impact theory, of course.[/glow]
But you are the one making the error of thinking about it as an either or issue. The fact of the matter is that the impact theory meets an extraordinary standard of evidence. No other theory has met that standard. It is not because of "impact theory chauvinism" that other theories are met with skepticism and calls for evidence, but because that is the way science is supposed to work. When someone makes a claim, they are asked to provide evidence. Scientists that have strong evidence in favor of a plausible theory do not simply give equal footing to a theory that does not have the same level of evidence in its favor. To ask the scientific community to abandon that method of ranking various theories is to abandon the idea of science altogether.

 

[Brian G Turner]

The idea of an impact being responsible for the Deccan Traps is merrely a suggestion that there may be other possibilities. I'm simply trying to break the "either/or" issue which is really my perception of how the issue is being presented in the scientific and general media.

I don't deny the K-T boundary shows a global event - but, as always, the primary question is what was the actual effect of the event. It does seem that too much speculation is being relied on. We know there is an impact. We know there was a mass extinction (though whether it was a short or sudden is still very contentious). But the idea that the impact therefore led to the mass extinction, in the absence of supporting mechanisms, is simply speculative. My rant above being based on this speculation being considered as "scientific evidence" - when this evidence simply says that something occured, but we do not understand the processes involved that may have led to the extinction (we can postulate the "nuclear winter" scenario, but again this is simply speculation and not quantifiable).

The Hell's Creek evidence I do not dismiss - what I was being dismissive of was applying the conclusions of local conditions to a global stage, when there is very much conflicting evidence to the contrary. There is by no means a clear sudden extinction excepting at a local level, with other geographic areas apparently showing gradual extinction in terms of millions of years. Which means that's there's a problem in relying too much on single locale data when inferring a global effect.

The idea that the Chicxulub crater could have been caused by a fragment is certainly an interesting and viable prospect - and would bring the whole impact theory far closer to the actual aim of explaining a sudden mass extinction. As I referred to before, I've read the impact camp stating that the Chicxulub event could not have had enough energy to cause the postulated global devastation - which immediately smells of fudge. Being more open with the possibility of multiple impacts thereofre opens a better playing field to work the theory on, but as you may have noticed, it's the single impoact that get's primary attention as a sole cause.

I think at the end of the day I simply hate the notion of "sole cause" in any complex system. Our understanding of vulcanism means that know that the Deccan Traps must have been having a significant effect on the global atmosphere, ergo also on the patterns of life on earth. And as I hopefully presented above, the whole issue of a single apocalyptic impact is actually quite contentious. Then again, when you really look at a number of more recent scientific theories you also enter areas of sometimes strong debate (Cosmology likely being the prime example).

I guess somewhere I just feel that the media itself is being too glib with the issue, white-washing a complex matter into black-and-white terms. In which case, perhaps this entire thread has less been about ascertaining the probability of impact theory, as much as questioning media presentation of the issue. Which means that if really I am ranting that the media doesn't present arguments very well, then I'm in hopelessly obvious waters and my objections to impact theory become pedantic.

 

[Survivor]

Okay, I get that you're disturbed by the way the media lumps theories into the catogories of "science" or "speculation" as though there is any nonspeculative science.

But you have chosen a poor topic for this discussion. And I don't know that you're operating with a clear understanding of the issues here either. A couple of times you've suggested that the K-T boundry isn't, without providing any evidence of this. If you want to contest an established theory, then you should really provide some evidence. Like the idea that the dinosaurs died out gradually over millions of years. I would need to see something published on that. Your objections to the Hell Creek evidence seem based on nothing more than personal bias, since it was part of a contiguous landmass that represented about half the land on Earth at the time we're talking about. And your distaste for the idea of a "sole cause" is obviously nothing more than that, personal distaste for the idea. When an organism dies suddenly rather than slowly, there almost always is an outstanding factor that caused death. The same is generally true of ecosystems and other homeostatic complex systems. That doesn't mean that such things never occur as a result of several small things happening coincidentally, but it is rare.

Also, I think that you are missing some key elements of a paleontologic mass extinction. The 70% figure was of species that are recorded in the fossil record. That means that large animals were way overrepresented in that extinction figure. The dinosaurs were sitting on the top of a very big food pyramid. A fairly minor (by modern standards) global environmental impact that affected part of the base of the food chain would cause almost all of the peak to collapse. The Deccan vulcanism wouldn't have injured plants worldwide, whereas a dust cloud would certainly have done so. None of the links that you have provided seem to point to significant criticisms.

I am sensitive to the fact that the Permian extinction probably was not caused by an impact...or at least not in a manner consistent with theories about the K-T extinction. I am also sure that in the popular media the Permian extinction (which is probably less well known simply because it didn't kill the dinosaurs) is usually something of a footnote, despite the fact that it is probably a more interesting extinction. But evidence of events that long ago is hard to come by. But I see little confabulation between the two. Paleontologists know the difference, and John Q. only cares about what killed the dinosaurs anyway, not what happened to the odd looking amphibians.

My problem is that your "rant" doesn't appear coherent or connected to the evidence. I could go on a dozen rants much stranger than yours, but I would feel compelled to back them up with evidence of some kind.

 

[Brian G Turner]

The problem I had with the Hell's Creek report is simply that it was a local study, whereas here was a report I cited purporting to be a wider global study, and yet concluded a gradual extinction worldwide.

The sole cause is indeed personal taste, but here it seems especially applicable in terms of there being a coinciding event with the volcanic eruptions of the Deccan Traps, which is believed to have caused global effects in terms of pollutant emissions, especially in terms of SO2.

Recent articles on the impact theory have stated that the Chicxulub event would not have had sufficient energies to cause the global devastation postulated in the classic model, and instead the theory is examining the idea that the key factor regarding the impact lies in the rocks being struck - notably, that is was a cloud of SO2 formed from the
original impact that caused the global devastation.

But, wait - this is precisely the cause already attributed to the Deccan Traps vulcanism. There is an incongruity forming here, not least because the theoretical effects of SO2 release from the Deccan Traps is already is already acknowledged to have a significant global impact.

The Iridium spike I certainly side with the impact model as being evidence of an extra-terrestrial impact. But the whole issue of targeting the Chicxulub crater as being the sole cause of global devastation (over any time period) just isn't being supported in the literature at the moment.

What makes discussion about this topic particularly difficult is that New Scientist keeps the majority of its articles unavailable online unless you're a subscriber, so I can't link to key articles I'd like to refer to.

The rant is especially rooted in the original italicised statement - there is far more contention and debate related to this issue than was being allowed by the author of that article. I guess that's simply what I'm reacting to - essentially, the dumbing down of such issues into tabloid "scientific fact".

Btw - do feel free to start your own rants, should you wish. I figured the purpose of a rant is simply to express frustration with a particular issue, rather than necessarily present a specific debate criteria backed by evidence.

 

[Survivor]

Hell Creek

[glow='2080a0',2,300]Fastovsky suggests that MacLeod failed to take into account the limitations of the fossil record. The only good records of dinosaurs in the last 10 million years of the Cretaceous, he says, come from western North America in the final two million years of this period. Others were not preserved, reducing the apparent diversity.
[/glow]

Evidence, evidence, evidence! In the only place that has a good fossil record of the K-T boundry, the evidence indicates that extinction was sudden. When you look at areas that do not have as good a fossil record of the K-T boundry, you can say that the extinction might have been gradual. That's like deliberately choosing to use a blurry picture of a perpetrator rather than a clear surveillance photo because that way it might have been your ex-wife, whereas the sharper photo excludes her as a suspect.

The Deccan vulcanism was clearly primarily lava flows. There is no way to know whether it injected a significant amount of contamination into the atmosphere. You are positing uncertainty as a reason to accept that theory, while using uncertainty over the exact effects of an impact to discredit the theory that you personally dislike.

Everything in a healthy scientific community is vigorously debated. If there is not debate over a theory, then that theory has become orthodoxy, and as such is no longer science. Physicists debate the idea that light-speed is really the absolute limit of propagation and whether the theory of relativity is correct. Cosmologists debate whether the Big Bang really happened. But in scientific debate, the evidence has to be the tie breaker between what is accepted as current science and what is not. And the preponderence of evidence is still on the side of the impact theory by a long margin.

That doesn't mean that it is "fact" for all time. Paleontologists can and should continue to look for evidence both for and against that theory as any other theory. But to attack the scientific community for siding with the evidence in this case is absurd. The scientific community should always side with the evidence. Otherwise there is no pressure on scientists to look for evidence to support their theories. Then it would be the "natural philosophy" community rather than the scientific community.

 

[Brian G Turner]

Okay, somewhere among that terrible blue glow is a statement that shoots down the gradual extinction theory - assuming it holds out to further research.

Anyway, I think this thread has served its purpose in terms of satisfying a rant - and regardless as to whether my protests were pointless or not, it;s been fun revisiting this topic.

I will indeed keep an eye out for further articles.

One of the most endearing thing about science - especially when you move towards cosmology and astrophysics - is the sheer expanse of mystery, debate, and contention that it has to ride on. It gives it an exciting edge - I had a great physics teacher all the way through secondary school (11-18 years of age), who effectively (perhaps inadvertently) taught myself that sciene is not about discovering answers, but about discovering new questions.

 

[Survivor]

: Sigh... :

I went ahead and fixed the "terrible blue glow" thing. But it isn't about discrediting gradual extinction, or the Deccan lava flows or whatever.

We have to accept that as science moves forward, our theories will be modified. Otherwise it is dogma rather than science. One of the most unfortunate setbacks of the scientific community is the evolution/creation debate, because evolution is now preached more dogmatically than creation ever was. But the fact remains that creationism is a load of crap. Science has not been well served by either camp, but at least the creationists have the excuse of not being actual members of the scientific community. The evidence now seriously suggests that life did not originate or even "evolve" on this planet, not as we currently understand the term. The cosmological evidence strongly suggests that we are not the most advanced species in the galaxy, or even close to being "advanced" by the standards that must apply to most existing intelligent species. But the UFO hysteria of the 50's has seemingly made the idea of advanced extraterrestrial intelligence anathema to most of the mainstream science community.

I'm glad that paleontologists and geologists in good standing can work on alternatives to the Impact theory of the extinction of the dinosaurs. But I'm also glad that the Impact theory is still regarded as the conventional explanation, because it has most of the good evidence on its side. When it doesn't, then it will have to be relegated to the status of an interesting coincidence (I personally believe that won't happen anytime soon, barring the discovery of a previously unknown geological record of the K-T boundry--or perhaps a means of looking back in time ala PastWatch). I see a healthy scientific debate that is based on and decided by the evidence, and that's all to the good. I can only wish that all other fields of science were as healthy.

 

[Brian G Turner]

LOL @:

"One of the most unfortunate setbacks of the scientific community is the evolution/creation debate, because evolution is now preached more dogmatically than creation ever was. But the fact remains that creationism is a load of crap. "

There was simply something in the way you said it - the entire debate summarised most concisely.

Yes - one of the frustrating points about the evolution camp is Richard Dawkins's quite outspoken attacks on religious/spiritual beliefs. It seems that if he cannot personally see something quantified, then that something cannot exist - a little amazing from someone claiming to support evolutionary theory, which still seems quite embryonic in terms of ratifying the mechanics. Shame we lost Stephen Jay Gould - never actually read much of his writings, but what I did appeared to have a thoughtful maturity about it. Dawkins, on the other hand, often seems to read as if he's ranting - and little different in attitude from the very people he rails against.

 

[Brian G Turner]

Just found the website for "nature" magazine, and noted one of their more recent news items was about controversy over analysis of the first drilled core samples from the Chx crater - claim being that that single impact could not have done the damage claimed by the classical "mass-extinction" scenario:

Mass-extinction controversy flares again

 

[Brian G Turner]

And just for the sake of it, here's an article on another possible extinction event from 380 million years ago, now being suggested as caused by an impact:

Second mass extinction linked to impact

Please note that this postulated impact occurs well before the Permian Extinction, which occurs around 250 million years ago.

 

[dwndrgn]

Ok, I am a science ignoramus...I barely followed those posts but it was invigorating in any case.

Take this with a huge pail of salt...

Couldn't an asteroid/meteor carry foreign bodies that could conceivably (how DO you spell that?) be anathema to the major food source for x dinosaur which happens to be the major food source for xx dinosaur...and so on? I realize you guys weren't debating this at all and I just wanted to toss in my two uneducated cents (they slept through school ;D).

 

[Brian G Turner]

Ssssshh! That's already one of my pet ideas I haven't told of! Actually, mine's a little more complicated that how you've described it. But you're right about the possible foreign body contamination. This is something that Chandra and co have been arguing for quite some time.

 

[Brian G Turner]

I just re-stated some pricinples objections elsewhere, and thought I may as well post them here:

Actually, I don't at all accept that the Chicxulub crater impact is a sole cause for the Cretaceous extinction. There simply isn't the evidence to suggest that a there is room for a sole cause.

Different studies highlight different aspects of the extinction - firstly, that there's is no sudden extinction, and secondly, that any sudden extinction is local-applicable only, ie, North America - which is precisely where all the supporting data for a sole-cause impact extinction comes from.

It's an essential point of note that the impact body *cannot* in dynamic terms actually provide the sufficient transfer of energy to cause of global extinction event. So US scientists "fudge" the issue by claiming that an undefined and entirely speculative "threshold" point was reached. As to the nature of the rocks in the Chicxulub crater - it's entirely speculative and unsupportable that this would have any bearing on the issue. Especially in comparision to the amount of sulphir churned out frmo the Deccan traps.

There's nothing wrong with including the impact event as part of a general long-term "period of extinction" which has multiple causes. One of the more interesting theories is that Chicxulub itselt could have been caused by a fragment of a larger extra-terrestrial impact event. But, again, there's a very real danger that even this is nothing more than a fudge to give an easy "one cause fits all" answer to an incontravertibly complex issue.

 

[Brian G Turner]

And now there's a project underway to take core samples from the Chicxulub crater:
Project to drill into 'dinosaur crater' gets under way - BBC News

Almost bizarrely, there's talk of looking for exotic life that may have formed there. Hedging their bets, or just an argument they had to use to gain the necessary funding?

 

[REBerg]

 

[J Riff]

Wow, great discussion. All I will say is - I think this is all going to straighten itself out, fairly soon. Our ancient history, that is. My first intimation of this came when looking at the pyramid at Giza, 50ish yrs. ago, and realizing that the hotshot scientists I was with - did't know what was what. I knew then that adults weren't so much of a much, and that this Earth was witholding secrets from us. But not forever, muah.*)

 

[Ray McCarthy]

or just an argument they had to use to gain the necessary funding?

yes.