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# Radiometric dating

(Redirected from Radioisotope dating)
Jump to: navigation, search 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. But new 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. Other methods such as Potassium-argon dating and Isochron dating are based on faulty assumptions and so unreliable as to be useless.

## Basic principles 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 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.

For example, in the 238U-206Pb series, 238U is the parent isotope and the others are daughter isotopes. 206Pb is the final daughter isotope and the one assayed in radiometric dating.

In order to calculate the age of the rock, geologists follow this procedure:

1. Measure the ratio of isotopes in the rock.
2. Observe the rate of radioactive decay from the mother to the daughter isotope.
3. Calculate the time required for the mother isotope to produce all the observed daughter isotope, according to this formula: $t={\frac {1}{\lambda }}\ln \left(1+{\frac {D}{P}}\right)$

where:

• t is the age of the specimen;
• D and P are the numbers of daughter and parent isotope today;
• λ is the decay constant for the parent atom.

The decay constant has dimensions of reciprocal seconds. In the special case in which parent and daughter atoms are present in equal quantities, the age of the specimen is the half-life of the parent isotope: $t^{{1/2}}={\frac {\ln 2}{\lambda }}$

Half-life (t1/2) is the amount of time required for one-half of the nuclei in a radioactive sample to decay into another kind of nucleus. 

## Assumptions

The various isotope dating methods rely upon several assumptions. They are:

1. Known amounts of daughter isotope (usually zero) at start.
2. No gain or loss of parent or daughter isotopes by any means other than radioactive decay (closed system).
3. 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 known, is the weakest assumption. For example, 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.

To understand this, recall the above formula. The greater the amount of daughter isotope, the greater the apparent age.

The proportion of argon to radioactive potassium in the sample today is observable, and the decay constant of potassium is readily calculable by measuring the amount of argon produced from the decay of 40K after a specified time. But the age of the rock and the proportion of argon to radio-potassium in the sample originally are not observable. As any first-year student of algebra soon learns, a single equation with two unknown variables cannot be solved. In fact, the above formula is far too simple, because it assumes that the amount of daughter isotope was zero at start. The formula below is a proper model that admits the possibility that some daughter isotope was present when the rock formed: $t={\frac {1}{\lambda }}\ln \left(1+{\frac {D-D_{0}}{P}}\right)$

where D0 is the amount of daughter isotope present at start. In order to simplify the formula, scientists generally assume that igneous rock contains no argon when it forms, because the argon, being a noble gas, would escape from the cooling lava.

This assumption has been repeatedly falsified. Fresh volcanic rock is routinely found to have argon in it when it first cools. In these cases, lava of a known age of no more than several thousand years (and in one case, no more than ten 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"

Numerous fossils have been found in strata inconsistent with the evolutionary model of Earth's history. These out of place fossils would seem to pose a problem for radiometric dating methods which are still calibrated based on the position of fossils (relative dates) in the geologic column. However, these fossils are not problematic if one simply disregards their existence.

If the date generated by isotope dating analysis agrees with the conventional interpretation of the geological column, paleontologists will accept it as valid. A date that disagrees with that interpretation is dismissed as an anomaly. This is not an example of malfeasance, but rather the result of assuming that the theory of evolution has been proved reliable, and therefore these seeming anomalies are due to contamination or other causes of analytical error. 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.

## Types of Radiometric Dating

• Carbon-14 dating: Uses the ratio of 14C to 12C to determine the age of biological remains. Contrary to popular belief, 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.
• Uranium-Lead dating
• Potassium-argon dating: K-Ar dating was used for a long time despite being challenged by creationists for its faulty assumptions and data. It is no longer defended 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, after K-Ar's faulty assumptions were exposed. 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.

## Problems

Main Page: Radiometric dating problems

Creationists have responded to this challenge in varying ways and cited 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 magnetars 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 global 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 and Mt. St. Helens. 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.

## Common Decay Series

Main Article: Radioactive decay