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Radiometric dating falsely assumes initial conditions are known (Talk.Origins)

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Response Article
This article (Radiometric dating falsely assumes initial conditions are known (Talk.Origins)) is a response to a rebuttal of a creationist claim published by Talk.Origins Archive under the title Index to Creationist Claims.

Claim CD002:

Radiometric dating falsely assumes that initial conditions are known, that none of the daughter components are in the mineral initially.

Source: Morris, Henry M., 1974. Scientific Creationism, Green Forest, AR: Master Books, p. 139.

CreationWiki response:

It needs to be noted that this book is more than 30 years old and new methods have been developed in that time, some of which are intended to fix this problem.

(Talk.Origins quotes in blue)

1. Isochron methods do not assume that the initial parent or daughter concentrations are known. In basic radiometric dating, a parent isotope (call it P) decays to a daughter isotope (D) at a predictable rate. The age can be calculated from the ratio daughter isotope to parent isotope in a sample. However, this assumes that we know how much of the daughter isotope was in the sample initially. (It also assumes that neither isotope entered or left the sample.)

With isochron dating, we also measure a different isotope of the same element as the daughter (call it D2), and we take measurements of several different minerals that formed at the same time from the same pool of materials. Instead of assuming a known amount of daughter isotope, we only assume that D/D2 is initially the same in all of the samples. Plotting P/D2 on the x axis and D/D2 on the y axis for several different samples gives a line that is initially horizontal. Over time, as P decays to D, the line remains straight, but its slope increases. The age of the sample can be calculated from the slope, and the initial concentration of the daughter element D is given by where the line meets the y axis. If D/D2 is not initially the same in all samples, the data points tend to scatter on the isochron diagram, rather than falling on a straight line.

It needs to be realized that the cited source predates isochron dating, so this is simply a case of the source's being out of date. However, the claim is still valid for most dating methods. At its core, Isochron dating assumes uniformitarian geology; therefore, if the rocks being measured were formed by processes outside that theory, such as the Genesis Flood, the dates derived by it are wrong. So while Isochron dating does not assume that none of the daughter components are present when the rock was formed, it still makes assumptions about the rocks' initial conditions. As such, the first part of this claim is essentially correct.

2. For some radiometric dating techniques, the assumed initial conditions are reasonable. For example:

The assumed initial conditions are reasonable inside uniformitarian geology, but not necessarily in flood geology or some other model.

  • K-Ar (potassium-argon) dating assumes that minerals form with no argon in them. Since argon is an inert gas, it will usually be excluded from forming crystals. This assumption can be tested by looking for argon in low-potassium minerals (such as quartz), which would not contain substantial argon daughter products. 40Ar/39Ar dating and K-Ar isochron dating can also identify the presence of initial excess argon.

So by Talk Origins' own admission the claim is essentially correct for potassium-argon dating. The question is whether or not the assumptions are reasonable. They are only reasonable inside uniformitarian geology. Even the most basic model based on the Genesis Flood would destroy the no-initial-argon assumption. One model that would destroy all three approaches is if the rocks were water-laid sediment rather than laid down in a volcanic eruption. In that case the rock would inherit the isotopic makeup of the source's material and thus make the rock's radiometric date earlier than it really is.

  • The concordia method is used on minerals, mostly zircon, that reject lead as they crystalize.

So by Talk Origins' own admission the claim is essentially correct for this method as well. Again, the question is whether the assumption is reasonable or not? It is only reasonable inside uniformitarian geology. According to the creation model these zircons were most probably formed on Day 3 of the creation week. They would have crystallized very quickly, if not instantaneously and therefore there would have been no time for total lead rejection.

  • Radiocarbon dating is based on the relative abundance of carbon-14 in the atmosphere when a plant or animal lived. This varies somewhat, but calibration with other techniques (such as dendrochronology) allows the variations to be corrected.

This makes carbon-14 accurate to a point, but carbon-14, dendrochronology and other methods are all mutually calibrated to each other. More importantly, they are all calibrated to uniformitarian geology. The results are different when the same data are interpreted by Flood geology.

  • Fission-track dating assumes that newly solidified minerals will not have fission tracks in them.

Of all assumptions given by Talk Origins, Fission-track dating is the only truly objective one, but it turns out that the calculations of fission-track decay constants are calibrated to other radiometric dating methods, particularly potassium-argon, and as such they are based on the same assumptions as potassium-argon. So it turns out that the original claim is correct once again.

See Also

Radiometric dating

Radiometric dating problems

Accelerated decay