Radiometric dating

Radiometric dating is a method of determining the age of an artifact by implausibly assuming that decay rates have been constant (see below for the flaws in that assumption) and measuring the amount of radioactive decay that has occurred. Radiometric dating is mostly used to determine the age of rocks, though a particular form of radiometric dating—called Radiocarbon dating—can date wood, cloth, skeletons, and other organic material.

Because radiometric dating fails to satisfy standards of testability and falsifiability, claims based on radiometric dating may fail to qualify under the Daubert standard for court-admissible scientific evidence. It is more accurate for shorter time periods (e.g., hundreds of years) during which control variables are less likely to change.

Radiometric dating (often called radioactive dating) is a technique used to date materials such as rocks, usually based on a comparison between the observed abundance of a naturally occurring radioactive isotope and its decay products, using known decay rates. It is the principal source of information about the absolute age of rocks and other geological features, including the age of the Earth itself, and can be used to date a wide range of natural and man-made materials. Together with stratigraphic principles, radiometric dating methods are used in geochronology to establish the geological time scale. Among the best-known techniques are radiocarbon dating, potassium-argon dating and uranium-lead dating. By allowing the establishment of geological timescales, it provides a significant source of information about the ages of fossils and the deduced rates of evolutionary change. Radiometric dating is also used to date archaeological materials, including ancient artifacts. Different methods of radiometric dating vary in the timescale over which they are accurate and the materials to which they can be applied.

Calibration

In order to calibrate radiometric dating methods, the methods need to be checked for accuracy against items with independently-known dates.

Carbon dating, with its much lower maximum theoretical range, is often used for dating items only hundreds and thousands of years old, so can be calibrated in its lower ranges by comparing results with artifacts who's ages are known from historical records.

Scientists have also attempted to extend the calibration range by comparing results to timber which has its age calculated by dendrochronology, but this has also been questioned because carbon dating is used to assist with working out dendrochronological ages.

Otherwise, calibration consists of comparing results with ages determined by other radiometric dating methods.

However, tests of radiometric dating methods have often shown that they do not agree with known ages of rocks that have been seen to form from volcanic eruptions in recent and historic times, and there are also examples of radiometric dating methods not agreeing with each other.

Young earth creationists therefore claim that radiometric dating methods are not reliable and can therefore not be used to disprove Biblical chronology.

Acceptance and reliability

Although radiometric dating methods are widely quoted by atheists, they are inappropriate for aging the entire universe due to likely variations in decay rates. Atheistic scientists insist that Earth is 4.6 billion years old while the Bible (the infallible word of God) suggests that the world to be around 6-10 thousand years old.

C14 dating was being discussed at a symposium on the prehistory of the Nile Valley. A famous American colleague, Professor Brew, briefly summarized a common attitude among archaeologists towards it, as follows:
"If a C14 date supports our theories, we put it in the main text. If it does not entirely contradict them, we put it in a footnote. And if it is completely 'out of date', we just drop it."
Few archaeologists who have concerned themselves with absolute chronology are innocent of having sometimes applied this method...

A geological guidebook published by the Queensland government acknowledges that the dates are not absolute, but must be interpreted:

Also, the relative ages [of the radiometric dating results] must always be consistent with the geological evidence. ... if a contradiction occurs, then the cause of the error needs to be established or the radiometric results are unacceptable

One example of scientists not accepting radiometric dates is that of Mungo Man, a human fossil from New South Wales. When originally found, it was dated by radiocarbon dating at around 30,000 years old. This was later revised to 40,000 years. Another scientist later used other methods to derive a date of 62,000 years. The original discoverer, unconvinced by this result, used a different method again, and again came up with a date of 40,000 years.

The fallibility of dating methods is also illustrated by the fact that dating laboratories are known to improve the likelihood of getting a "correct" date by asking for the expected date of the item. For example, the Sample Record Sheet for the University of Waikato Radiocarbon Dating Laboratory asks for the estimated age, the basis for the estimate, and the maximum and minimum acceptable ages.

Some major methods of radiometric dating

There are several major types of radiometric dating in use:

1. Radiocarbon dating, also called carbon dating
2. Potassium-argon dating
3. Uranium-lead dating
4. Uranium-thorium
5. Rubidium-strontium dating

Explanation by Analogy

No method exists for measuring time, except by measuring it as it is passing. Therefore, the age of an artifact must be calculated.

The basic principle in any dating method is to find a process that is occurring at a measurable rate and which is causing a change, measure the rate of that process, work out what state the artifact was in at the beginning of the process, observe what state it is in now, and to calculate how long the process at the measured rate would need to occur to effect that change.

For example, to work out how long a candle has been burning, the following steps would be needed:

1. Measure how long it takes the candle to burn down a given amount.
2. Find out how long the candle was when it started burning.
3. Measure how long the candle is now.
4. Calculate the difference between the two lengths.
5. Calculate how long it would need to burn in order to burn that length.

For most radiometric dating methods, one radioactive element changes by a process of nuclear decay into another element (often through a number of intermediate steps). For example, uranium will eventually decay into lead. So to measure how old a specimen containing some uranium and some lead is, the following steps are required:

1. Measure the decay rate of uranium.
2. Find out how much uranium was in the specimen to start with (this might be done by assuming that all the lead was originally uranium).
3. Find out how much uranium is in the specimen now.
4. Calculate how much uranium has turned into lead.
5. Calculate how long it would take that much uranium to turn into lead, given the measured rate. Calculations involve the well-established function for exponential decay: <math>F</math>_{<math>t</math>}<math>=e</math>^{<math>-kt</math>}.

Bibliography

• Lamb, Andrew, Carbon dating into the future 24th March, 2007 (Creation Ministries International).
• Faure, G. and Mensing, T., Isotopes: Principles and Applications, Wiley & Sons, 2005.
• Walker, M., Quarternary Dating Methods, Wiley & Sons, 2005.
• Walker, Tas., Radioactive decay rate depends on chemical environment, Journal of Creation 14(1):4–5, April 2000.
• Walker, Tas., The way it really is: little-known facts about radiometric dating, Creation 24(4):20–23, September 2002.