Radiometric dating

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Mass spectrometer used to determine the proportions of isotopes contained in a sample of igneous rock.
Mass spectrometer used to determine the proportions of isotopes contained in a sample of igneous rock.

Radiometric dating utilizes the decay rates of certain radioactive atoms to date rocks or artifacts. Uniformitarian geologists consider this form of dating strong evidence that the Earth is billions of years old. However, research by creationists has revealed a large number of problems with radiometric dating. In some cases such as Carbon-14 dating, radioactive dating actually gives strong evidence for a young Earth, while other methods such as K-Ar dating and Isochron dating are based on faulty assumptions and so unreliable as to be useless.

Contents

Types of Radiometric Dating

  • Carbon-14 dating: Carbon-14 dating gives solid evidence for a young Earth;
  • Helium diffusion: This dating method, developed by creationists, is based on the rate of Helium diffusion from zircons, which gives many rocks a maximum age of 6,000 +/- 2,000 years.
  • Potassium - Argon dating: (K-Ar) dating was used for a long period despite being challenged by creationists for its faulty assumptions and data; it is no longer held up as reliable, even by uniformitarian geologists, because it is entirely dependent on the assumption that igneous rocks never have any Argon when they initially cool, and that assumption has been repeatedly demonstrated to be false as igneous rock of known age has been "dating" to ages far older than its actual age, because there was Argon in it when it formed.
  • Concordia dating: Concordia dating rests on the same assumptions as K-Ar, namely that there was none of the daughter isotope (in this case Lead) in the sample when it originally cooled. Like the assumption in K-Ar, however, this assumption is also unfalsifiable, making this method equally unreliable.
  • Isochron dating: Isochron dating was introduced as an attempted substitute for K-Ar dating, due to K-Ar's faulty assumptions. However, Isochron dating bears faulty assumptions of its own. It assumes the homogeneity of the sample when it originally formed, an assumption which is always false in whole rocks, and unfalsifiable in minerals.

Isotope Dating

Parent and daughter isotopes commonly used to establish ages of rocks.
Parent and daughter isotopes commonly used to establish ages of rocks.

Many atoms (or elements) exist as numerous varieties called isotopes, some of which are radioactive, meaning they decay over time by losing particles. Radiometric dating is based on the decay rate of these radioactive isotopes into stable nonradioactive isotopes. To date an object, scientists measure the quantity of parent and daughter isotope in a sample, and use the atomic decay rate to determine its possible age.

In the Image:u238.gif - Image:pb206.gif series, Image:u238.gif is the parent isotope and the others are daughter isotopes. Image:pb206.gif is the final daughter isotope and the one used in radiometric dating.

In order to calculate the age of the rock, the following procedure is followed:

  • The ratio of isotopes in the rock is measured;
  • The rate of radioactive decay from the mother to the daughter isotope is observed;
  • It is assumed that there was none of the daughter isotope in the original rock, even though the composition of the original rock cannot be observed.
  • It is calculated how long it would take for the mother isotope to produce all of the observed daughter isotope, assuming there was none of the daughter isotope in the rock when it was originally formed.

Assumptions

The various isotope dating methods rely upon several assumptions - the main assumption being that all daughter isotopes are the result of decay over time to the exclusion of other possible sources or processes. It is also assumed that the sample in question exists in a closed system. Such a closed system does not really exist, but open system effects can't be determined easily, so for many methods it is simply hoped that the ratios are at equilibrium.

These methods all have the same basic assumptions:

  • Known amounts of daughter isotope at start;
  • No gain or loss of parent or daughter isotopes;
  • A constant decay rate;

Challenging the assumption of original composition

The first assumption, that the amount of the daughter isotope in the original rock, is the weakest assumption. K-Ar dating assumes that there was no Argon in the original rock. But if there was argon in the rock when it originally formed, then the age calculated will be millions of years too high.

The reason for this is simple algebra. Rocks are dated according to the following formula:

Age of rock = ((Argon in sample today) - (Argon in sample originally) / (Potassium in sample today)) x (Halflife of Potassium).

The Argon in the sample today is observable, the Potassium in the sample today is observable, and the Halflife of Potassium is observable. But the age of the rock and the amount of Argon in the sample originally are not observable.

As a matter of basic ninth grade algebra, A single equation with two unknown variables cannot be solved. If the scientist assumes that there was no Argon in the rock when it was originally formed, but there was, then the scientist's calculation will be wrong: he will calculate the age of the rock far too high.

It is generally assumed by scientists that rocks have no Argon in them when they form, because, it is believed, the Argon would be gas, and would therefore escape from the molten rock.

However, this assumption has been repeatedly demonstrated to be untrue. Fresh volcanic rock is routinely found to have Argon in it when it first cools.[1] In these cases, lava of a known age of no more than several thousand years had argon in it when it formed, so that the rock was calculated by K-Ar dating to be millions of years old, even though it was known to be only thousands of years old.

"Calibration" and disregarding "Out of Place Fossils"

All radiometric dating methods are still calibrated to relative dates in the geologic column. If the date that is generated by isotope analysis agrees with the conventional interpretation of the geological column, it is accepted as valid, while dates that are in disagreement are dismissed as an anomaly. This is not an example of malfeasance, but rather the result of assuming that the theory of evolution has been proven reliable, and therefore these seeming anomalies are concluded to be due to factors such as contamination. These out of place fossils or rocks are not considered a reason to question the theory. This makes independent testing of these dating methods impossible, since published discrepant dates are rare.

Creationist Responses

Main Page: Radiometric dating problems

Creationists have responded to this challenge in varying ways and citing numerous problems with radiometric dating. Creationists admit that there is significant evidence of daughter isotopes well in excess of what could be generated by decay at contemporary observed rates within the timescale they contend to be true.

Some have proposed that the errors could be attributable to excess original daughter isotopes (though isochron dating methods minimize this) and accelerated decay caused by external phenomena. While astronomers have found that Magnestars emit radiation that could cause bouts of accelerated decay, and that these bouts may be more common than originally thought, the amount of heat produced by the radiation during the short period presents a problem for creationists.

A more common approach is to allow for accelerated nuclear decay during the early portion of terrestrial history, when those elements which decay naturally were buried far below the crust (or far below the waters of the Biblical flood, in some models), therefore dealing with the heat problem. One possibility for the accelerated decay comes with the possibility of variable speed of light. Other theories simply hypothesize that during certain periods of time God sped up the process, these are called singularities in creation science.

In addition to the above methods of dealing with this challenge, creationists have contended a whole raft of problems with both the older and newer methods of radiometric dating. They cite several examples of discordant dates when multiple methods are tried on the same rock, many anecdotes of dating techniques giving obviously wrong data (including some where rock formed after 1900 was dated as being over 3 million years, such as at Mt. Ngauruhoe. John Woodmorappe claims that discrepancy in data is prevalent, and accuses scientists of throwing out most of the inaccurate results, giving the illusion of accuracy. He also indicates how mixed families of rock can give anomalous isochron readings, some of which would indicate a negative age for certain rocks. His book, The Mythology of Modern Dating Methods, documents approximately 200 quotes by secular geologists indicating problems with the various dating methods.

Radioactive Decay Series

References

The radioisotope age dating book and DVD set by the RATE group - (Purchasing Info)
The radioisotope age dating book and DVD set by the RATE group - (Purchasing Info)

Creationist References

Secular References


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See Also

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