Your position is one of false premises, and false dichotomies. To pick an example. Diatoms. Why did half of the diatoms suffer extinction, and the other half survive? First off the question implies a false dichotomy that if some went extinct, then all should have suffered extinction, this isn't true. Secondly, the question ignores the simple observational fact that not all species of diatoms live in the same environment, and not all Diatoms will be subjected to the same stressors by a single event. Even amongst the macrofauna there are some readily discernable patterns, for example, those species that appear to have suffered less attrition are those that were capable of seeking shelter for extended periods in damp places or fresh water environments. Why did Australian Marsupials survive where North American marsupials did not? Please Register or Log in to view the hidden image! Geography and climate may have been a factor in this. (and queue the next ridiculous question "But why didn't dinosaurs survive in Australia").
I'm not ignoring anything. You can read about it generally here: http://en.wikipedia.org/wiki/Cretaceous–Tertiary_extinction_event I particularly like the last paragraph: "In a review article, J. David Archibald and David E. Fastovsky discussed a scenario combining three major postulated causes: volcanism, marine regression, and extraterrestrial impact. In this scenario, terrestrial and marine communities were stressed by the changes in and loss of habitats. Dinosaurs, as the largest vertebrates, were the first to be affected by environmental changes, and their diversity declined. At the same time, particulate materials from volcanism cooled and dried areas of the globe. Then, an impact event occurred, causing collapses in photosynthesis-based food chains, both in the already-stressed terrestrial food chains and in the marine food chains. The major difference between this hypothesis and the single-cause hypotheses is that its proponents view the suggested single causes as either not sufficient in strength to cause the extinctions or not likely to produce the taxonomic pattern of the extinction." I believe the jury is still out, and scientists are still looking for more information on this. But some people have already reached firm conclusions, and don't want to look any further.
In science, the jury is always still out. Even with the firmest conclusions. I agree that a person should not disregard further study. However, I also think a person should not ignore a mountain of evidence in favor of a foothill of one. Rather, they should try to determine what single model most accurately describes what occurrences led to both sets of evidence.
Technicaly, this is an ad-hominem, but I would precisly expect you to make a comment like this. Besides which, at this point your entire argument is based on "I can't imagine a causal mechanism therefore there is none". Some times extinction is as simple as not being able to migrate fast enough to keep up with your niche and the climate zone that it exists in.
Quite the opposite. Obviously there is a causal mechanism, we just haven't been able to prove exactly what it was. Clearly the meteorite impact might well have had something to do with it, as it does occur quite close in time to the extinctions. But to what extent, and how, is not known. That is, the causal connection is not established so far as I can tell. Of course, any regionally located species directly impacted (squished by the meteorite) would have been impacted. But how did species on the other side of the globe die out, and why did closely related species in their orders not die out. Those are the causal connections not explained.
Utter bullocks. Alvarez Hypothesis on Wiki If nothing else the global distribution of Iridium should be enough to tell you that your assertions are ill founded. Besides which, what about this statement: Excludes the possibility of some ecosystems being pre-stressed?
"triggering" is quite a lot different than "causing". You still haven't explained how the event caused the extinction of the dinosaurs; or do you subscribe to the earliest 'explanation' that they all died within a matter of days/weeks from starvation? If you think simply positing an asteroid strike explains things, then you might as well pack your bags and go home, 'cause you're not really interested in the causation - how did it happen? It's almost certainly far more complex of an analysis than anything you've imagined thus far - and we're still elucidating information that goes towards that analysis. And I've been well aware of the global distribution of Iridium since it was first reported in 1980
This has to be some of the most ignorant BS I've seen you post on this thread so far, even if for no other reason than the position you're attributing to me is directly contradicted by posts I've made on this thread. I'm well aware of the complexities involved, which is PRECISELY WHY I keep refering back to specific examples, and stating them as examples. Really? Because your posts suggest otherwise (for example your suggestion that the asteroid would only kill those dinosaurs that got squashed by it). To illustrate a couple of the points that either you've been ignoring, or you're ignorant of. The global distribution of Iridium suggests a global distribution of dust after the impact. There's evidence for virtually global forest fires as a result of the impact. Your biggest problem is that you're thinking too small mindedly, which is funny because that's essentially what you've just gotten through accusing me of. You strike me as being of the ilk that suggested that Alvarez's hypothesis was nonesense because they thought that it meant that one stone had to fall from the sky for every dinosaur.
I really don't get where you're coming from with your blatantly hostile ad hominems, and your sense that you've read my mind, when in fact you haven't the foggiest clue. I never suggested that only critters directly impacted/squished would be the ones that died, and no others. Certainly the shock wave alone would have gone for quite some distance. And yes, Walter was reporting a global distribution from the dust of a pulverized asteroid. So what. How does that explain the cause of the extinction of the dinosaurs, when so many other species continued onward, including the ancestors of our own? I'm still looking for the causation, which you don't seem to be providing.
I read that when it first came out in paper, probably 1978. Great book indeed. I generally prefer Niven's solo work, but that collaboration with Pournelle was a good one. There were a lot of nice little touches, like the guy realizing he was looking at the last case of Perrier he would ever see. It had a somewhat more positively optimistic ending than The Postman, which I also enjoyed. (Never saw the movie.) * * * * NOTE FROM (ANOTHER) MODERATOR * * * * This is a place of science and you of all people know how the scientific method works. Your assertion was challenged because you provided no evidence. The obligation is yours to do so. This is reasonable since it should be much easier for you to track down one of your own sources than for the challenger to find it. In the future please respond appropriately to challenges and keep the discussions moving forward. Even if the language is not always scholarly in tone.
Thankyou for pointing that out Fraggle. Walter. To summarize the global effects of the Chixculub impact. Shock CO[sub]2[/sub] production from the decomposition of carbonates. The introduction of tens of thousands of cubic kilometers of vaporized rock into the atmosphere. Burning off at least 25% of the global vegetation. The earthquakes and volcanic eruptions that would have been generated around the world. It's been estimated that the temperature of the surface of the continents may have dropped by as much as 40 K, and that the light levels may have fallen below the levels required for photosynthesis for several months. The currents created by the thousand foot high tsunamis would have dragged the anoxic water up from the depths (or some of it anyway) and resulted in at least a partial oceanic turnover. I've seen at least one paper looking at dinoflagellates, coccolithophora, and diatoms that suggests that one of the factors that may have contributed to the survival of some species, but not others, is resistance to acid rain. The point that I have endeavored to make, and that you appear to have repeatedly failed to understand is that there wasn't necessarily any single feature that enabled one species to survive, where another did not, and there wasn't necessarily any single causal mechanism generated by the impact that resulted in the death of one species and survival of another. Also, your comments appear to ignore subtelties such as the point that what may have been a survival feature at the time of the impact, could have lead a species to extinction after the impact (for example the increase in surface temperature for about a century after the impact generated by the sudden introduction of a couple of hundred gigatons into the atmosphere in a period of seconds to hours). So a species that initially survived the cold, the collapse of the food chain, and the loss of sunlight might have perished with the increased surface temperatures as the atmosphere cleared.
So how does pointing out that critters directly squished by the impact implies that they are the only ones that would be killed? Your whole attitude is of reading things into my posts that simply aren't there. Elsewhere I mentioned the shock front that would be deadly - certainly not death by being directly squished by the asteroid. So what exactly do you believe you've added that wasn't already present in the Wikipedia article I cited, one of the easiest of references to find. I believe your list of extinct critters is contained in that article. What I'm still looking for is the causation mechanism - and you've suggested some. But what features, for example, of the dinosaurs caused them to go extinct, whereas similarly sized animals such as mammals did not. That is what I thought the subject of your post was, and there simply wasn't much there other than 'the asteroid did it'. And I did cite that last paragraph in the Wikipedia article which references the idea that it was simply a triggering event of other processes already in effect.
The context of the rest of your posts in this thread, combined with your words. The fact that in the previous sentence you are once again complaining about the perceived lack of a causal mechanism. The sentence amounts to "There is no causal mechanism to kill all of the Dinosaurs, but, I can accept that those in the impact zone would have died". I simply used your language. Only after I mirrored your claim back at you, so it doesn't count in this context. So then you agree that the causal mechanism is plainly stated in the wikipedia article? Awesome, we can move on from this discussion then. Oh wait, no, we can't. Tell me Walter, would it help if I translated the phrase "There wasn't neccessarily one single feature that caused the extinction of the dinosaurs". I've even pointed out some of the similarities between those species that made it through the extinction intact.
Yep, it would help. Did they all die within weeks/months of the event, say from starvation? Or did they survive for years, engaging in a slow decline, with some even lasting thousands of years. Or do you not have any idea either. That would be a nice causation explanation. As I said, I don't have a good handle on the causation as of yet, even if the triggering event was an asteroid.
I would have thought that the phrases like "The collapse of the food chain" would have been fairly self explanatory in this regard. And I've already stated that my understanding is that it's GENERALLY expected that they died out in the days, or years following the impact - remembering that I've already explained to you that the immediate environmental effects of the impact could/would have persisted for up to a century after the impact. Here is what I understand through the Paleontology that I have studied. The primary cause is the collapse of the food chain. It's generally expected that the light levels would have been too low for a period of months, perhaps as much as a year, after the impact for photosynthesis to occur. Those that tended to survive, as I understand it, tended to be omnivorous, carrion eaters, benthic scavengers, deposit feeders, or insectivorous. Consider also, as I have previoulsy mentioned that if you examine land based vertebrates, according to Sheehan and Fastovsky, for example, only 12% of land dwelling vertebrates survived, but 90% of the species in fresh water assemblages survived (also don't forget that the recovery was uneven). According to Sheehan and Hansen: Remembering that birds evolved from dinosaurs, one of the patterns that emerges from those species that survive (that I can recall) is that they tended to be small, and capable of seeking shelter under ground, under rocks, or in trees (not the foliage neccessarily mind). There's also some evidence to suggest that ability to withstand acid rain was important. The temperature would have dropped by 40k. I blieve I have also previously stated that I expect that some species may have survived the initial impact, and subsequent collapse of the foodchain, and maybe even the drop in temperature, only to be wiped out by the rapid rise in temperature that followed it. Once the dust cleared, which potentially took a decade or more, the CO[sub]2[/sub] injected into the atmosphere (most estimates I have seen place it in the hundred of gigatons) would have caused the temperature to increase rapidly (if you accept anthropogenic global warming, then this period may be the closest natural analog to the current situation). So just from a preliminary analysis, there's some causal mechanisms right there: Ability to withstand the collapse of the food chain. Ability to withstand Acid Rain Ability to withstand extended periods of darkness Ability to seek shelter for extended periods. ability to withstand rapid (on a scale of decades) and extreme (temperature variations in excess of 40k) variations in climate.
Now you're starting to get some causation. So, did all of the dinosaurs did out immediately (days/weeks/months), or did some species continue to breed/reproduce for years/decades/centuries, while they decreased in numbers towards extinction?
There's an irony in here somewhere I'm sure. As I understand it, it's generally expected that if the food chain collapsed, then for the most part it would have been over and done with within about month. Having said that though, there isn't neccessarily a way of distinguishing timescales on lets say less than 100 years in most records from that time. Based on my understanding, most of the dying would have occured in less than a year, however, this does not preclude the possibility of extinction of species being driven by rapid climate change after the impact, nor does it preclude the possibility that the impact might have pressured some species to the point of an irrecoverable decline leading to an inevitable extinction. I believe that even today there is an endangerment category reserved for species for which that is true.
To put things in some perspective. If you make the simplifying assumption that the vaporized rock material that was ejected by the impact, which some estimates put at 500 gigatons, was well mixed in the troposphere and stratosphere, you get an average concentration of 19000 μg/m[sup]3[/sup] of what would effectively have been PM10 (as the rock vapour cooled and condensed it would have crystalized into very fine dust) over the entire surface of the globe. To put this in perspective, the WHO guidelines are 20 μg/m[sup]3[/sup], and the worst polluted cities in the world are still 'only' on the order of 200-300 μg/m[sup]3[/sup].
