101 Ways To Kill The Dinosaurs

blank writes "Everyone knows there are many impact craters on Earth; around 170 in fact. This article from the Seattle PI points out that more than one of those impacts could have caused the extinction of the Dinosaurs. In Ukraine, scientists found that a well-known crater had been inaccurately dated - the correct date puts the impact sometime around when the Dinosaurs disappeared..."

Comments

Far side

[macdaddy357]

Remember the Far Side cartoon entitled what really killed the dinosaurs? They were all smoking. That is on of the all time classics. I'd post a link if I knew of one.

Simple really

[infonography]

Politics killed them, that and lawsuits over patents, copyrights, and anti-trust. I wonder if we could work the DMCA into it some where. Or we could just ask Strom Thurmond.

Re:Simple really

[Anonymous Coward]

I think H-1B hunters came to Earth, so the dino's retreated to Mars or something.

For pete's sake.

[Neck_of_the_Woods]

You would think they would just realize the it might have been more than one. Look at last 1/2 dozen that smaked into Jupiter.

Nothing like a one two punch to really put a cloud in the sky and cool things down.

Agreed.

[Captain_Stupendous]

When you think about it, it makes a hell of a lot more sense that an earth-covering cloud of crap would come from a series of impacts, rather than just a single huge one.

1) Asteroids, meteorites and comets tend (okay, massive generalisation here, but whatever) to travel in packs (a la Leonides and Perseides).

2) I don't kow about you, but I have trouble believing that a single impact could wipe out "all" life without destroying the planet, ripping off the atmosphere, etc...

Re:Agreed.

[AlXtreme]

My thoughts exactly, problem is that this must be one huge (numbers and size) pack to devastate the earth, as many would miss their target.

Imho there must have been a major collision relativly close to earth that caused for hurling massive amounts of relativly small asteroids at earth. The chance that a random "pack" of asteroids would all hit earth without direct cause seems to me to be very slim...

Re:Agreed.

[GayBliss]

But all life was not destroyed. There are many species that did not become extinct during that time. I don't think an impact from any object is necessary to explain the dinosaur disappearance. The earth is going through one the largest mass extinctions in its history right now. No impact required.

Effects on Radioactive dating

[BCGlorfindel]

Does anyone with a better knowledge of radioactive dating than me know what kind of effect these impacts have on radioactive dating methods? Would there be any, and if so on what scale? Furthermore how localized would the effects be, and finally how could/are they compensated for? The part of the article about how few craters have been accurately dated got me wondering about what kind of complications they presented for dating methods in the area around them.

Re:Effects on Radioactive dating

[Anonymous Coward]

The impact itself would not adversely affect radiometric dating techniques in terms of screwing up decay rates, or isotopic ratios, etc. That's all misinformed FUD that you might hear people spew.

While I'm a geologist who has done a lot of radiometric dating (U-Pb and 40Ar/39Ar), I don't know much about how this particular crater is being dated. However, I can imagine that the heating and melting caused by an impact event actually HELPS you date the event.

Consider a rock. It may have some amount of 40K and 235U and 238U and 232Th that decay over time. The daughter products of those decays (39Ar from K and 206Pb and 207Pb from the U and Th) accumulate within the rock (actually within specific crystals, but I won't get into details) over time. The minerals, however, are only closed systems below a certain temperature (it varies depending on the specific mineral) called the closure temperature. Above the closure temperature, solid state diffusion creates an open system and the daughter products can escape from the crystal structure.

Now if the impact hits and melts the target rocks (heating them way above the closure temperatures of any minerals they may contain), the radiometric clocks in the target materials will be reset! Once the melt cools and solidifies, though, the "rock clocks" will become closed systems again, and radiogenic daughter products will accumulate again.

The best material to go after from the melted target would be stuff that quickly cooled to form glass. Things like tektites. Since they are glassy, we know they cooled very quickly (too fast to form mineral grains). So dating glassy tektites (probably with 40Ar/39Ar, a fancy variant of K-Ar dating) is one way to pinpoint the timing of the impact.

Re:Effects on Radioactive dating

[young-earth]

what kind of effect these impacts have on radioactive dating methods?

Radiometric dating has so many problems that it probably wouldn't effect it at all.

Every dating done on a known-age volcanic rock has resulted in wildly inaccurate data. Example: Mt. St. Helens rocks were dated at (varies by sample, that alone should raise red flags about the radiometric dating concept) values ranging from 350,000 to 2,800,000 years. The samples came from the dome, which was known to be 8 years old at the time of the testing. Apologists for radiometric dating respond that this is a case of poorly selected samples; yet they have no counter-example of a well-chosen sample that shows the correct date. Nor do they answer how to know that tests in other sites are correctly chosen, aside from their rather vicious ad hominem attacks.

Further examples: the Hualalai volcano, which erupted in 1800-1801, was tested at 1,600,000 years old. The Etna volcano eruption of 1792 is dated at 1,410,000 years ago. There are many others but that makes the point - radiometric dating is badly flawed, from K-Ar to C14 to isochrons to Ru-Sr and the rest.

So since every case where the age of a rock is known the measured age is wrong, on what basis is the assumption made that rocks where the age is unknown that the methods are correct?

Science is supposed to be about repeatable experiments with falsifiability criteria. Falsification of radiometric dating is simple: find a rock of known age, if the test can't repeatedly produce the correct answer, then the method is not accurate. So it's time to find another dating method that does produce repeatably correct results with known age samples.

Re:Effects on Radioactive dating

[jericho4.0]

Just because radiometric dating can give wildly inacurate results, doesn't invalidate it. Any signifigant heating of a rock after it is formed can drive of daughter atoms, giving it a younger date than it really is.

Incomplete melting or cooking in other gases can give a higher date. Geologists take radiometric dating with a grain of salt for that reason

Re:Effects on Radioactive dating

[young-earth]

Thanks for your honest reply:

Just because radiometric dating can give wildly inacurate results, doesn't invalidate it.

But please consider this point: what other measurement techniques are widely used, quoted to the public as absolute truth, taught in schools as authoritative, yet have such a description from a defender of them?

And consider the definition of science as requiring both falsifiability and repeatable experiments. Can you cite an example of a known-age rock that was repeatedly accurately dated? If not, then the only proven results of radiometric dating are those that point out its inaccuracies, and there are none that prove its accuracy.

Yes of course many things make radiometric dates potentially inaccurate, such as heating too much or too little, leaching, initial conditions that are other than assumed, proximity to sources of radioactivity, diffusion, etc.

But any measurement used in science needs to be proven to be accurate before it's blindly accepted, and radiometric dating has not achieved that.

Take Carbon-14 as another case. Live mollusks have been tested and, were they able to be surprised, they would have had their shells knocked off by the news that they have been dead for 2300 years according to C14 dating. Or take the writing of Dr. Robert Lee in the Anthropological Journal of Canada in 1981:

The troubles of the radiocarbon dating method are undeniably deep and serious. Despite 35 years of technological refinement and better understanding, the underlying assumptions have been strongly challenged, and warnings are out that radiocarbon may soon find itself in a crisis situation. Continuing use of the method depends on a fix-it-as-we-go approach, allowing for contamination here, fractionation there, and calibration whenever possible. It should be no surprise then, that fully half of the dates are rejected. The wonder is, surely, that the remaining half has come to be accepted.... No matter how useful it is, though, the radiocarbon method is still not capable of yielding accurate and reliable results. There are gross discrepancies, the chronology is uneven and relative, and the accepted dates are actually the selected dates.

Re:Effects on Radioactive dating

[jericho4.0]

I'm going to guess from your nick that this is a bit of a pet subject for you. :-)

I can't cite examples. I belive that there are problems with the technique, and that there have been wildly inacurate results published as fact. I do think, though, that science can take uncertianty into account, and still provide valuable insight.

One thing I'm not sure about; when you say 'known age' do you mean 'known to be 2.3 million years old' or ' formed in lava 10 years ago'. As far as I know, there is no other way to date very old rocks than through radiometric dating, and inacuricies in younger rocks doesn't prove much.

Re:Effects on Radioactive dating

[Anonymous Coward]

every case you cite are attempts to apply radiometric dating to exceedingly young samples. of course it doesn't work! you have to have samples old enough for there to have been enough decay for there to be a measureable amount of daughter product. otherwise the signal to noise ratio in even the best mass spectrometer will give shit data -- there's not enough signal!

Re:Effects on Radioactive dating

[young-earth]

Allowing the point you have made, the bottom line result remains: there is no known case of a known-age sample (age known via a completely different method) that tested accurately and repeatably. Yes you may say the problem is we only absolutely know the ages of things that are so young that they cannot be accurately measured due to variations in initial conditions or contamination levels of decay products.

However the conclusion remains: radiometric dating has never been verified by anything other than radiometric dating. That is circular reasoning, and it is not a valid basis for science.

Re:Effects on Radioactive dating

[Anonymous Coward]

the validity of the theory behind radiometric dating is without question. radioactive decay is solid. each radiometric system has it's own complexities, yes, but those complexities are well understood. the weak link is the geologic context of samples used in dating.

there is no way to "please" you in that there is no "brute force" way to prove the techniques in the manner you describe. nevertheless, the theory behind radiometric dating is well understood. moreover, mutiple dates using different systems of material from the same sample have been shown to give consistent results (a rather important and reproducible result you seem to shrug off).

do you have more substantive objections to radiometric dating? have you indeed studied or been trained in the theory behind the various techniques? i hope we can have more in depth discussion of the potential problems behind the techniques than just the naive observation that young samples don't work so good.

Re: Effects on Radioactive dating

[Black Parrot]

> Does anyone with a better knowledge of radioactive dating than me know what kind of effect these impacts have on radioactive dating methods?

Hope springs eternal in creationists' breasts.

Re:Effects on Radioactive dating

[young-earth]

Citing qualifications is not IMHO a useful endeavor. The facts are more useful.

And yes your insight is quite correct - there is no way to validate the method. However your assertion that the only weak link is the geologic context is, I believe, a bit of an understatement. While the geologic surroundings are quite important, so are simple things like: if the rock is exposed to air and sunlight, diffusion of Ar will be accelerated over a rock buried in a glacier. Similarly a fast-moving stream or river will cause leaching which can effect several of the minerals used in dating.

But perhaps most significant are the assumptions made about both the initial conditions and about the time between formation and measurement. Initial conditions which are not known can have a profound effect on the measurements. And the assumption underlying all of this is generally referred to as "uniformitarianism". To the reader who may be unfamiliar with this term, that is a reference to the assumption that everything is today as it has been in the past, that there were no major disruptions in the environment, that gradual change is the only agent of change.

The opposing theory to uniformitarianism admits that we don't know what conditions were like thousands of years ago, that radioactive decay might be effected by, for example, a neutrino burst from a supernova, or from a different phenomenon that we can't explain today. It also asserts that the Grand Canyon, for example, was not formed over billions of years, but was actually formed far more rapidly (and there is strong evidence of that being the case).

Re:Effects on Radioactive dating

[Anonymous Coward]

>if the rock is exposed to air and sunlight, diffusion of Ar will be accelerated over a rock buried in a glacier

i'm sorry but that's pure nonsense. exposure to air or sunlight at the earth's surface will NOT affect volume diffusion of Ar in geologic materials. even the lowest closure temperature systems routinely used for 40Ar/39Ar, K-feldspar, have closure temperatures of ca. 150 degrees C. below that temperature, you'll have to wait around a hell of a long time before you get any appreciable diffusion of Ar out of the crystal.

>Similarly a fast-moving stream or river will cause leaching which can effect several of the minerals used in dating

again, no. can you please give me an example of the scenario's you have in mind. alteration of minerals by hydrothermal fluids will affect the dates you get. for instance, you can alter micas (muscovite and biotite) to chlorite which will give you a huge component of "extraneous" 40Ar. but that's what i mean by geologic context being the weak link. if you are a geologist worth his salt, you wouldn't try to date a rock that's been heavily altered, especially if the micas have been chloritized.

i know all about uniformitarianism and catastrophism (the "opposite" worldview). however, appealing to catastrophism for exotic wasys of screwing up radiometric dating is a bit of a stretch. explain to me exactly how a nutrino burst would affect radioactive decay, for instance.

finally, the most recent research points to the grand canyon being cut within the last 5 million years. i don't think anyone has thought it's taken billions of years to cut (at least no one's thought that for a long time).

Re:Effects on Radioactive dating

[young-earth]

Just one simple point for your claim that dates are repeatable inside one rock. Check out

C.S. Pickles, S.P. Kelley, S.M. Reddy and J. Wheeler, "Determination of High Spatial Resolution Argon Isotope Variations in Metamorphic Biotites," Geochemica et Cosmochimica Acta, 61 (1997): pp.3809-3833

for the conclusion:

128 Ar isotopic analyses were obtained from ten profiles across biotite grains in high-grade metamorphic rocks, and Ar-Ar ages within individual grains ranged from 161Ma-514Ma

That's a factor of better than 3 for the range.

How do you explain that one?

Re:Effects on Radioactive dating

[Anonymous Coward]

If you cared to read the rest of the abstract (and indeed the rest of the article as I did) you would see that the age profiles the authors obtained are diffusion profiles. To wit (from the abstract):

"These apparent age variations cannot be explained by chemical alteration and require diffusion of excess argon into the grains...The age profiles show a remarkable fit to theoretically derived curves for volume diffusion of argon."

Re:Effects on Radioactive dating

[young-earth]

I didn't dispute the fact that it fits the model for volume diffusion; I was addressing your claim in your post:

mutiple dates using different systems of material from the same sample have been shown to give consistent results (a rather important and reproducible result you seem to shrug off)

which this paper clearly refutes.

Re:Effects on Radioactive dating

[fluffy666]

Every dating done on a known-age volcanic rock has resulted in wildly inaccurate data. Example: Mt. St. Helens rocks were dated at (varies by sample, that alone should raise red flags about the radiometric dating concept) values ranging from 350,000 to 2,800,000 years.

This was the dating of phenocrysts and xenoliths - rocks that soldified before the eruption. Strange you failed to mention this. Of course, if you are talking about a 500 million year old rock, a systematic error of 2 million years isn't that important.

There are many others but that makes the point - radiometric dating is badly flawed, from K-Ar to C14 to isochrons to Ru-Sr and the rest.

I'd like to see how you think isochrons are flawed. Radiometric dating does have independant testing - different methods can be used on the same rock, and importantly, relative dating techniques can be applied (superposition, timing of fault movement, etc.). There is no way of other physical processes systematicaly changing the dates - a neutron flux would, for instance, make some dates look much younger and others much older. Changing basic physical constants has the same effect.

One independant technique that has been used successfully is that of sea floor dating. Since we know where - and at what temperature - sea floor crust is formed, we can calculate how old it is according to the depth using heat flow calculations. These calculated dates agree with the radiometric dates, AND dates calculated from sea floor spreading rates. So three independant methods all agree.

Re:Effects on Radioactive dating

[Anonymous Coward]

re: sea floor calculations - you're still making assumptions about uniformatarian conditions... without those assumptions, neither of your two calibrating methods would yield the results you desire.

Re:Effects on Radioactive dating

[fluffy666]

So you are claiming...

a) That several different radiometric dates 'just happen' to agree.

b) That this value *also* agrees with thermal conduction/contraction models, and

c) That this value *also* agrees with ages derived from spreading rates, and

That this is all a coincidence.

Could you perhaps explain to me a model that has a different age *and* accounts for all of this? Remember that if you start changing the laws of physics for one, it'll rebound for the others.

Or will you just run away?

Re:Effects on Radioactive dating

[Anonymous Coward]

Will you ignore the fact that radiometric dating frequently produces different answers for one set of samples, and that the "correct" date is then selected? Will you ignore the fact that the most widely accepted model of continental drift now in favor is one put forward by a creationist, as his computer model explains things that nothing else does?

I do not have the depth of expertise to fully answer to your satisfaction the issues you have brought up, but I know there are answers available in several books. Are you open-minded enough to read them?

Re:Effects on Radioactive dating

[Anonymous Coward]

>the most widely accepted model of continental drift now in favor is one put forward by a creationist, as his computer model explains things that nothing else does?

that's very interesting. please elaborate on this.

Re:Effects on Radioactive dating

[Anonymous Coward]

I'm at work now, no access to materials, so I can only refer you to John Baumgardner's work as being the authority on this.

Re:Effects on Radioactive dating

[fluffy666]

Will you ignore the fact that radiometric dating frequently produces different answers for one set of samples, and that the "correct" date is then selected?

Experimental error happens. Indeed, creationists go to great lengths to find examples of such:

Bad dates

The data is taken from a creationist publication that mined the literature for examples of bad dates - yet they STILL average out to being correct!

Will you ignore the fact that the most widely accepted model of continental drift now in favor is one put forward by a creationist, as his computer model explains things that nothing else does?

What, this one?

Flood/catastrophic plate tectonics model

You do realise that this model implies that the entire ocean floor was created in a year? Given that the oceanic crust is 6km thick and covers 53% of the planet, this implies that the entire ocean was boiled off. This model is not 'widely accepted', it is wrong.

Problems with floods..

You have, of course, still failed to answer with regard to the thermal gradients and cooling in the oceans, why all the different radiometric techniques give the same age, and why the ages agree with those given by continental drift extrapolation. Hell, I even have to post your arguments or you!

The question is not my open-mindedness - I'm fully prepared to take creationist arguments on their merits. You are the one dismissing science without even learning about it first. THAT is closed mindedness and you know it.

Re:Effects on Radioactive dating

[cp99]

Will you ignore the fact that radiometric dating frequently produces different answers for one set of samples, and that the "correct" date is then selected?

Now would be the time were you present some supporting information on this slur that you've just cast on the scientific community. I know that I'll be waiting in vain for you to supply some.

Will you ignore the fact that the most widely accepted model of continental drift now in favor is one put forward by a creationist, as his computer model explains things that nothing else does?

What objective evidence do you have for his model being the most widely accepted?

Re:Effects on Radioactive dating

[cp99]

It is a bit of a pet subject for young-earth. He or she has an ideology to defend, and will hence use what ever it takes to support it.

To use his mollusc example, radiodating is frequently very bad to the point of being useless on very young samples (the definition of very young depends on the technique). Also, carbon dating requires that the organisms derive their carbon from the atmosphere. Molluscs get very little of their carbon from the atmosphere.

The creationists have take a system which is well known to geologists to be bad for carbon dating, applied it anyway, and use the results to discredit radiodating.

However, the only thing which they discredit, is any claim of honest or integrity which they once may have had.

Re:Effects on Radioactive dating

[Anonymous Coward]

Re: supporting information on the selective use of dating - check out G. Brent Dalrymple's paper in the early 60's where he documented this (before he became dogmatic). But for an authoritative discussion on the problems, see the publication "Mythology of Modern Dating Methods" by John Woodmorappe. It is incredibly dry reading, but answers all your objections (and those of talkorigins which are typically specious).

Re:Effects on Radioactive dating

[cp99]

So, do I have this right, your evidence is a paper from the 60's, and another work by a creationist well known for trying to mislead others.

This article shows how your reference plays up small differences in dating.

Carbon Dating.

[Nyphur]

An interesting note is that many objects that hit the earth contain radioactive isotopes of carbon, which can mess with the carbon-dating technique used to date the craters. As an object of such mass and velocity to cause the destruction of the dinosaurs would vapourise on impact, covering the crater with this radioactive Carbon isotope.

There was a small mountain with a lake and trees coverign it etc somewhere that was dated as much older than the earth itself, because if the readioactive Carbon caused by such a collision. Actually, that radioactive carbon is what heats the lake: It's a regular paradise :)

Re:Carbon Dating.

[Anonymous Coward]

14C dating is NOT used to date the extinction event that killed the dinosaurs. That was 65 million years ago. 14C is only useful for things 50,000 years old AT THE OLDEST.

Re:Carbon Dating.

[GrimSean]

Since Carbon-14 has a half-life of 5.73 x 10^3 years, I really doubt that your mountain was dated using it. Craters (and other geological formations, such as you mountain) are not dated using it as it's half-life is only about 5 or 6 thousand years, meaning it's only useful to date back approximately 70 thousand years, as any specimens from before that would have to be made entirely out of C-14 for any of it to survive to modern times. It's interesting to note that we are screwing over archeologists of the future thanks to the industrial revolution - there is more C-14 present in the atmosphere now due to pollutants (Nitrogen + neutron = Carbon-14). Potassium-40 and Uranium-238 are the isotopes used to date old rocks, as their half-lives are 1.26 x 10^9 years and 4.5 x 10^9 years respectfully. It is most likely that the crater in question in the above article was inaccurately dated due to an abundance of the isotope used to date it being present in the meteor that caused it.

Re:Carbon Dating.

[j_w_d]

As others have no doubt pointed out, you misunderstand what radiometric dating is, and more importantly, you seem to be missing something about the nature of radio-carbon, such as where it comes from, its half-life, and its application in archaeological and paleontological dating.

First C-14 is the only readioactive form of carbon used for radiometric dating. No physical collision at any speed that occurs in the earth's vicinity could produce it. The isotope is produced by the interaction of cosmic rays and N-14 (that is a nitrogen isotope). The C-14 later decays reverting to N-14 and emitting a neutrino. The produciton of C-14 takes place within the earth's atmosphere. The atmosphere alone contains enough gas in any form to act as a significant source to donate radiocarbon into the biosphere. No significant amount of carbon arrives from space and no C-12 coming from space could have any significance to the production of C-14; they are not related, and C-12 plays no roll in the existence of C-14.

Second, who ever told you about the "small mountain" had a serious case of rectal-cranial inversion. Additional radiocarbon would cause an organic mass to appear younger, not older, though many thoroughly confused and consistently ignorant creationists persist in thinking the opposite.

Last and most important, radiocarbon has a half-life of about 50,000 years and a useabilility range for dating purposes of about 100,000 years at best, if accelerated mass spectroscopy dating methods are employed. Since dinosaurs disappeared from the planet about 70,000,000 years ago, radiocarbon is useless, because about 1400 half-lives of radio carbon have passed. For practical purposes that means that there is no C-14 left in any sample you look at.

Re:Carbon Dating.

[Anonymous Coward]

You claim creationists have things backwards, and you claim the half-life of C14 is 50,000 years? And that's not a typo on your part since you then multiply 50000 times 1400 to get 70E6.

Next time you choose to slam a group of people, you'd better be a little more accurate in your own facts. The half-life of C14 is 5730 years by most estimates, though some labs have slightly different figures.

Re:Carbon Dating.

[j_w_d]

You are correct. The 50,000 was the result of me hurrying. I added an extra zero there when I entered what was intended as a rounded figure in the calculator, then stupidly repeated it when I (accurately) transcribed my mistake, and carefully punctuated it. The two common half-life figures I am familiar with are the Libby half-life of 5568 +/- 30 years and the Cambridge figure of 5730 +/- 40 years which you mention. This of course puts the Cretaceous about 14,000 radiocarbon half-lifes away, not the mere 1,400 I had came up with there.

Thanks for the correction. It is why there is peer review in science.

Multiple Impacts

[ZahrGnosis]

I wouldn't be surprised if the dinosaurs died off as a result of a multiple-impact object, instead of a single crater. Something similar to what
Shoemaker-Levy 9 did to Jupiter. Are there any known examples of related impact sites on earth? I imagine that'd be hard to prove, but it would be a neat piece of trivia.

I killed the dinosaurs

[A55M0NKEY]

I went back in time and infected them with the flu. They all died.

Nanananana

[Anonymous Coward]

Mirror Matter Mindy Moop

Error margins?

[Confuse Ed]

re:

Example: Mt. St. Helens rocks were dated at (varies by sample, that alone should raise red flags about the radiometric dating concept) values ranging from 350,000 to 2,800,000 years

<RantMode>

Why do people (the 'media' in particular) always miss out the error margins when quoting scientific results? The first thing you should learn when doing any form of quantitative science is error analysis: without this all the results are meaningless as you have no idea of the certainty or significance of them.

For example, with these results you quote, if the measured result were actually 2.8 Million years +/- 2 million years, then that would not give any cause for concern, or 350 thousand years +/- 10 million years would be as good as spot on. OTOH if the results were 2.8 Million +/- 1 year then we should definitely be questioning the accuracy of such measurements.

<RantMode>

Catastrophism vs. Gradualism

[Psion]

Let's not forget that many species of dinosaurs were in decline well before the k-t event that is generally accepted as the point (65mya) when dinosaurs went extinct. Although the idea of a big rock killing all the dinosaurs is popular with geologists and catastrophists, many paleontologists still don't buy this explanation. Some even point to birds as the direct descendents of theropods and insist that dinosaurs never really went extinct in the first place.

Re:Catastrophism vs. Gradualism

[fluffy666]

Events at the KT boundary:

1: Long term climate change, over 10 million years or so; a fairly gradual cooling with changes in sea level. Makes the dinosaurs less energy efficient.

2: Medium term, repeated massive volcanic events in the Deccan Traps. These would cause repeated climatic fluctuations; again this is bad for the big animals.

3: Short term, one or more asteroid collisions causing a very severe short term climatic shock.

It's worth pointing out that if you have any one of these in isolation - which has happened many times - you do NOT get an extinction on the KT scale. Personally I go for the 'It was everything at once what diddit' theory.

Re:Catastrophism vs. Gradualism

[tiedyejeremy]

Add to your theory of combined events (Gradualism) the discovery of the propensity of late theropods to nesting and body coverings and the very well reasoned theories that thermoregulation by internal means would have been required and you have the natural progression from large meat eaters to smaller and smaller animals that could have survived the gradual onset of the K-T extinction - which is no extinction at all; merely a rapid evolutionary step from dinosauria to avions!

and also the precursory event leading to my run on thoughts and sentences...

From The Simpsons....

[CastrTroy]

Homer: Oh, a book of Gary Larson Cartoons. I don't get it(flips page), I don't get it(flips page), I don't get it(flips page), .......