Proving Evolution: Post 1 - Dating Methods

First, a note on the title of the series of posts. Science does NOT "prove" things. Anything. Ever. (No, really... not anything). "Proof" is for math and alcohol. What we are really talking about here is "evidentially supported to the greatest extent manageable". But if you say that then people who don't understand science just declare "Aha! But you didn't PROVE it!" ...as if that was relevant. So, we end up with titles like this. Any science purists out ther who are outraged at the inexact terminology, my abject apologies.

Now, getting down to things. This is a series of posts I wrote up a long, long time ago while banging my head against the brick wall that is "people on the internet who believe in Creationism". I think it does a pretty decent job of covering a LOT of information while maintaining a balance between being not so technical the average non-scientific type can't understand it if they take a real shot at it... but technical enough that it remains accurate and not distorted by horrendous over-simplification.  I'll be throwing them up here over he next week or so.

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Dating Methods


Carbon (C14) Dating:

C14 dating is used to date the remains of organic, air breathing organisms up to approximately 50,000 years old. While living these organisms breathe the atmosphere, which contains trace amounts of the radioactive isotope Carbon 14 that is constantly being produced in the upper atmosphere through neutron bombardment. So long as they are alive the C14 content of their bodies will remain in equilibrium with the C14 content of the atmosphere. When they die respiration ceases, along with the intake of any new quantities of C14. Over time the C14 decays with a half-life of 5568 years into N14. By measuring how much C14 remains un-decayed the time elapsed since the death of the organism can be determined.

A common misperception of C14 dating is that it relies on the assumption that atmospheric C14 levels remained constant in the past so that we can know how much C14 an organism started off with. While this was an assumption made when the technique was first developed about half a century ago it has not been the case for several decades. Historical atmospheric C14 concentrations have been charted and calibrated using both dendochronology and lake varves which incorporate organic sediment in their annual deposition layers. One particularly good example of this is Lake Suigetsu in Japan where cores have been drilled to a depth of 45,000 annual layers. Because of the layering process we have an independent count of exactly how old every layer is… and because the layers incorporate organic material (the remains of a surface algae which dies off every year and sinks to the bottom of the lake) each layer can be C14 dated as well, and using these two data points the atmospheric C14 content can be charted all the way back for the entire time span encompassed by the varve core. This data (cross-checked against multiple other sites and methods) then allows us to apply C14 dating to other sites already knowing how fluctuations in atmospheric C14 concentrations in the past will effect the results… and allowing us to calibrate out error that would otherwise be introduced due to those past fluctuations.

Just one more note on C14 dating... once this calibration scale was applied it was discovered that previous C14 dates had been underestimating ages. By a few percent. There are also the occasional examples of C14 dates which have supposedly been wildly inaccurate. Many of these examples are the result of grossly improper applications of the method. For example, one I have encountered quite often is the "C14 dating of a living snail shell" that came back as thousands of years old... I believe this is one of Hovind's pet illustrations. The mollusks in question were extremely inappropriate subjects for C14 dating, which anyone familiar with the method would know. They form shells which are in equilibrium with the carbon content of the water sources in which they live... NOT the atmosphere. No C14 lab worth it's salt would ever date such an organism without warning the person requesting the test of the reservoir effect that would most likely render the test results invalid.

Longer Ranged Radiometric Dating:

There are a great many longer ranged radiometric dating methods using radioactive isotopes with longer half-lives than C14. I’ll quickly review a couple of them.

1. Argon-Argon (Ar40-Ar39) dating. Argon-Argon is a method closely related to Potassium-Argon, where the age of a sample is determined by measurement of how much of the potassium-40 in the rock has decayed into Argon-40. However, with the Argon-Argon method it is also possible to tell if there is any Argon-40 present which is NOT a product of the decay of the potassium in the sample. This is done by placing the sample to be dated in close proximity to a nuclear reactor for several hours. The resulting neutron bombardment from the reactor causes potassium-39 in the sample to be transformed into Argon-39. Argon-39 has a half-life of only 269 years, and is not found in nature… so any subsequently detected argon-39 is known to be a product of the decay of the potassium-39 in the sample. After this is done the sample is then put through an incremental heating process and the released argon-40/argon-39 ratios are measured at every stage. A sample that contains only argon-40 that is a product of the decay of the potassium-40 in that sample will release argon-39 and argon-40 in the same proportion at EVERY heating step. If there is parentless argon-40 in the sample that is not a product of the decay of that sample’s potassium-40 however the ratios will change at different heating stages. This eliminates the popular claim that excess parentless argon in a sample can cause that sample to date as older than it really is.

2. Rubidium-Strontium (Rb-Sr) dating. Very useful for dating igneous rocks in particular. There are many different isotopes of Strontium (Sr-87, Sr-86, etc…). Rubidium-87 decays into Strontium-87. When magma first cools into an igneous rock formation all parts of the rock will have the same ratio of strontium-87/strontium-86 because the isotopes are freely dispersing through the molten rock prior to that time. However, once the rock hardens different parts of the rock will have different rubidium/strontium ratios than others since the atomic make-up of rubidium is larger than that of all the strontium isotopes and it will be incorporated into the structure of some minerals more or less easily than that of others. From that point on the rubidium will continue decaying into strontium-87… and the areas of the rock with higher initial ratios of rubidium/strontium will have their concentrations of strontium-87 increase at a higher rate than those with a lower ratio of rubidium-strontium. By taking multiple measurements from different sections of a sample and plotting their final ratios of strontium-87 to other strontium isotopes which, not being byproducts of the radioactive decay of other elements, have remained stable since the formation of the rock… the initial ratios of those isotopes throughout the sample can be determined and the elapsed time since the samples formation is established. Again, this method is highly resistant to any objections that we have to assume the concentrations of the isotopes in the samples being dated in order to date them. That is simply not the case. The initial concentrations are experimentally determined.

For further info on the various radiometric dating methods, and since (I believe) all the other participants in this discussion are Christians, I would highly recommend this page:

Radiometric Dating

Dr. Wiens goes into considerably greater detail than I have, there’s the added advantage of several visual aids, and he’s not a godless atheist like me for those that tend to distrust us as a matter of principle… just in case there are any of those reading along.

Constancy of Decay Rates

For my last point in this post I’ll address one more often-encountered claim. That we just assume that decay rates have remained constant over time. This is not true. The constancy of decay rates over time has been independently established by multiple tests. Among them the isotopic analysis of the byproducts of the Oklo Natural Fission Reactor at Gabon which establish that decay rates have undergone absolutely no detectable change for a minimum of the past 1.8 billion years. There is also an entire battery of interstellar observations that can be made that would detect a past alteration of decay rates since that would require a change of the fine structure constant of the universe… with quite readily observable effects. Effects which are never observed no matter how far away (and thus how old) the object is we are looking at.

And that is a summary of the “evolutionary” position on dating methods. The dates arrived at are accepted and used in establishing ancient evolutionary timelines, ages of fossils, etc... because there is extremely solid evidentiary support for the reliability of those methods.