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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..."
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.
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.
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.
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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:
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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.
I don't need to be made to look evil. I can do that on my own. - Christopher Walken
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!
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.