The Geologic Column

Didn't see this actually answered yet:

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Redstang writes:
When the concept of the geologic column was first established, how did they know what dates to give each layer?

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The dates were not known with any certainty or accuracy before the advent of radiometric dating. The relative ordering of layers was, of course, obvious, and there was much speculation about both the age of the earth and the age of individual layers.In the last decade before the 20th century Lord Kelvin estimated the age of the earth at no more than 24 million years based upon thermodynamic estimates of how long it would have taken the molten earth to cool. Geologists and biologists felt their own evidence supported a much greater age, hundreds of millions of years, and so a sort of compromise concensus age of around 100 million years served for a while.This uneasy compromise was short-lived, for in the early 1900s radioactivity was discovered, and it was quickly realized that the heat from radioactive materials in the earth's core would have slowed cooling, thereby pushing back the age of the earth considerably. Application of the principles of radioactive decay to dating minerals quickly followed, initially with just the uranium/lead method, later by more accurate and less error prone methods such as potassium/argon and rubidium/strontium. The age of individual geological layers was quickly established, thereby also proving what had previously been only an assumption, that a geologic layer had the same age wherever found in the world.Geologists and biologists were gratified that Lord Kelvin's estimate was far too young, but were as staggered as everyone else as ongoing efforts pushed the antiquity of the earth first into the hundreds of millions of years, then past a billion years, then past billions of years, finally arriving at the current consensus age of 4.56 billion years.--Percy

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Redstang writes:
... it is usual to obtain a spectrum of discordant dates and to select the concentration of highest values as the correct age. (Armstrong and Besancon).

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... the thing to do is get a sequence of dates and throw out those that are vastly anomalous. (Curtis et al)

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Do you really believe that scientists who are cooking the data are also admitting it publicly? These quotes are probably genuine because most Creationist quotes of scientists are genuine, but they're very likely taken way out of context, and the one from Curtis is very hard to figure. Perhaps the quote is from a joke he told at a party. A search of the web reveals that your "Curtis et al" is Garniss Curtis, a well-known geochronologist. If you look at this critique of Woodmorappe you can see that what Curtis considers "vastly anomalous" is when he can't get agreement anywhere close to 1%, and even then the last thing he would do, indeed the last thing any respectable scientist would do, is "throw out" the anomalous dates. And if they did do it they'd never, ever, admit it.It helps to bring some simple common sense to some of the quotes you're going to see from Creationist sources. Perhaps it would help to turn it around and think how likely it would be that Creationists would say wildly negative things about Creationism. If someone quoted a Creationist saying something like, "Creationist criticisms of radiometric dating are largely without merit," wouldn't you be a bit skeptical? You would, right? So would I, and I'm an evolutionist. It just makes sense that people wouldn't go around ripping the very things they deeply believe in.So when you see Creationist quotes of geologists ripping their own science to which they've devoted their lives, you might try casting a skeptical eye.Anyway, the link describes where dating of the same layer using two different methods yielded dates of 32.5 and 34.4 million years, a difference of only 6%. A mere 6% difference is probably not what you had in mind when you saw the term "vastly anomalous."You can be sure radiometric dating is not false and scientists are not simply, in effect, pulling dates out of a hat because of the fact that scientists have not fractured into many opposing camps, each with their own favorite set of dates. If the results of radiometric dating were largely random and unreliable we'd have situations such as one group claiming the dinosaurs became extinct 65 million years ago, others claiming it was only 35 million years ago, and yet others saying it was 100 million years ago. The reason there are no such dramatic disagreements but instead extremely broad consensus among scientists about the age of the geologic layers is because radiometric dating gives consistent and accurate results.Your closing lengthy excerpt comes from ICR Impact No. 307 by Andrew A. Snelling. His claim that Brent Dalrymple's early work contradicts his later claims is the opposite of what is actually the case.Brent Dalrymple is a well-known, one might even say famous, geochronologist. He did much of the landmark work establishing the guidelines and baselines for more accurate potassium/argon dating, and part of this work entailed measuring Ar-40 levels in relatively young lava flows to make certain that Ar-40 actually did evaporate from the hot lava. One additional thing he verified was that intrusions (basalt from lava that didn't make it all the way to the surface but rather became trapped within or between geologic layers) cannot be reliably dated using K/Ar dating because the Ar-40 had no opportunity to escape into the atmosphere and so is still trapped in the rock.If you look at reference #3 for where Snelling says he got the dates that he attributed to Dalrymple you'll see that the reference is not to Dalrymple but from Snelling himself. Snelling's text attributes the dates to Dalrymple, but in reality they come from a different Snelling paper. Follow the link in reference #3 to this Snelling paper titled The Cause of Anomalous Potassium-Argon "Ages" for Recent Andesite Flows at Mt Ngauruhoe, New Zealand, and the Implications for Potassium-Argon "Dating" and you'll see the 7 dates of young basalts that actually come from Dalrymple are less than 2 million years old. Since K/Ar dating is only used for material older than 50 million years, a possible residual amount of Ar-40 at levels measured by Dalrymple could cause no more than a 2 million year descrepancy, and Dalrymple's work help establish guidelines for correcting even that small error.Snelling then goes on to list a number of other Ar-40 measurements of young basalts, but he never provides references for these numbers, and they're certainly not Dalrymple's. Most of the dates are much less than 50 million years, but some of them are huge, like 580, 690 and 700 million years, and if true it would mean that K/Ar dating is largely unreliable. But if that were the case then K/Ar dating could not yield the consistent results that it does.So something is wildly wrong with Snelling's numbers. I see some of the oldest dates come from volcanoes near the ocean, and lava under water solidifies far too rapidly for the Ar-40 to escape, so perhaps that explains these old dates, but there's no way to tell for sure.Bottom line: Snelling's data is a ringing indictment of radiometric dating, but his numbers are unattributed and suspect, and don't jive with reality anyway.--Percy

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xxx writes:
Mark, can you say honestly that you really understand this dating method and all the inner workings of it?

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Radiometric dating is so simple anyone can understand it. You only have to know the following, and I'm sure you already know most of it:

• An atom consists of a nucleus composed of protons and neutrons surrounded by orbiting electrons.
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• The type of an element is governed by the number of protons in the nucleus. Potassium (K) has 19 protons in it's nucleaus, while argon (Ar) has 18.
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• An element's atomic weight is the sum of the protons and neutrons in the nucleus, since protons and neutrons weigh approximately the same.
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• While an element always has the same number of protons in the nucleus, the number of neutrons can vary. The atoms of an element with different numbers of neutrons are known as isotopes. In the case of potassium, by far the most common isotope is K-39, meaning that most potassium atoms have 19 protons and 20 neutrons. The most common isotope of argon has 18 protrons and 22 neutrons for an atomic weight of 40.
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• Some isotopes are unstable, meaning they spontaneously decay to become a different element through the loss of a proton. In the case of K/Ar dating, K-40 is unstable and can spontaneously decay to Ar-40.
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• The rate of decay is specified in terms of the half-life. The half-life of K-40 is 1.25 billion years, meaning that it takes 1.25 billion years for half the K-40 in a sample to decay to Ar-40.
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• The age of a sample is determined by measuring the ratio between the parent and daughter materials, ie, between K-40 and Ar-40. The proportion of K-40 that has decayed to Ar-40 combined with the half life gives you the age. I can provide you the actual equations if you like.

Now I have to take back some of my opening statement. K/Ar is the simplest of dating methods. The isochron methods are more complex, and in the last couple decades new techniques have become available that are even more complex.In geologic layers that contain materials amenable to more than one dating technique, the dates are found to agree a great preponderance of the time.--Percy

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Redstang writes:
One of the ironies of the evolution-creation debate is that the creationists have accepted the mistaken notion that the fossil record shows a detailed and orderly progression and they have gone to great lengths to accommodate this `fact’ in their flood geology.

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Raup, David M. Evolution and the fossil record Science, Vol. 213 (July 17, 1981) p. 289

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Raup is a well known mainstream paleontologist, and this quote is not something a mainstream paleontologist would say. A search of the web for this quote finds it with both more and less surrounding context, but otherwise always the same.The obvious question is one often asked: What is the point of quoting scientists appearing to say something they obviously don't believe? If scientists actually believed the things Creationists make them appear to be saying then many scientists must reject evolution. But this is simply not the case, so what sense is one to make of these quotes?I've looked up this quote, and Raup writes precisely what he is quoted as saying, but, as expected, it's been taking out of context. The quotation is from the concluding paragraph of a much longer letter.When taken all by itself, this quote appears to be conceding that the geological column does not contain a record of change over time. But in the body of the letter Raup is taking issue with the common but erroneous view that evolutionary change is one of orderly progress. He explains that this is definitely not the case, and compares it more to price fluctuations on Wall Street. So when Raup in his conclusion denies "a detailed and orderly progression" in the fossil record, he isn't saying it isn't a record of change, but merely that it isn't a record of orderly progress.Gould often says the same thing, that not only is the fossil record not one of progress, but that it isn't even possible to predict how life will respond to selection pressures. There are simply too many factors involved. Life gets bigger and smaller, obtains eyesight and loses it, obtains legs and loses them, leaves the sea and returns. This isn't an orderly progression, and that's all Raup was saying.--PercyPS - If anyone's interested in the full text of the Raup letter just let me know.