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Radiometric Dating or How Old is that Rock?

See also


How Old is the Earth and Universe?

Radiometric dating gives the Earth an age of about 4.5 billion years and the Universe an age of about 17 billion years.  The accuracy of radiometric dating is often checked by comparing the radiometric date with non-radiometric dates of objects, such as historical accounts, tree rings, ice cores, etc.  These results repeatedly demonstrate the validity of radiometric dating.

There are over 40 different radiometric dating methods.  Each has it own application, limitations, and dating range.

See also How Old is the Earth? for a more detailed discussion

See also Young Earth Evidence

Want an in-depth knowledge of how the age of the Earth is determined?
Read The Age of the Earth by G. Brent Dalrymple


How Radiometric Dating Works

Some of the Primary Radiometric Dating Methods

Parent Daughter Half Life(years) Dating Range(years) Items Typically Dated
Uranium-238 Lead-206 4.5 billion Greater than 10 million Zircon, Uraninite.
Uranium-235 Lead-207 704 million Greater than 10 million Zircon, Uraninite.
Potassium-40 Argon-40 1.3 billion Greater than 100,000 Muscovite, Biotite, volcanic rocks.
Rubidium-87 Strontium-87 49 billion Greater than 10 million Muscovite, Biotite, Metamorphic or Igneous rocks.
Carbon-14 Nitrogen-14 5,730 100- 40,000 Wood, Charcoal, Peat, Bone, Tissue, Carbonates.

General history of radiometric and Carbon-14 dating

In depth description of dating written for Christians

An Essay on Radiometric Dating By Jonathan Woolf

Isochron Dating

Other radiometric dating sites


How do we know that radiometric dating methods are accurate?

The accuracy of radiometric dating is often checked by comparing the radiometric date with non-radiometric dates of objects, such as historical accounts, tree rings, ice cores, etc.  These results repeatedly demonstrate the validity of radiometric dating.  Carbon-14 dating has been extensively tested against known historical items, such as King Tut's wooden coffin, with excellent results.  See Lake Suigetsu Algae for another such example.  While there are occasional false dates caused by contamination and leaching, overall, radiometric dating has been demonstrated to be very accurate.  Critics make much use of these false dates.  But just because radiometric dating doesn't work every time, this doesn't mean that it doesn't work.  After all, just because Detroit produces a lemon once in awhile, that doesn't mean they can't make cars.

The accuracy of argon radioisotope dating has been verified by testing it against known volcanic eruptions showing that it is accurate.

Event Biblical events have been accurately dated using Carbon-14.  A tunnel believed to be built by King Hezekiah and described in the Bible (Kings II 20:20; Chronicles II 32:3, 4), was dated using carbon-14 and uranium-thorium dating to show that it was built near the time of the Judean king (700 B.C.).


The Dead Sea Scrolls:  Some papyrus manuscripts contain exact dates when they were written and others have been dated using paleography, a method of determining a date from the style of characters.  Carbon-14 dating gives the same dates.

Why do recent lava flows date to thousands
of years old when radiometrically dated?

Also the samples are dated using various isotopes giving matching results.  If radiometric dating wasn't accurate, then for this to happen, the decay rate for each different isotope would have to have changed by the same amount and contamination and leakage of many different elements in the sample would have to be equivalent.

Want to Learn More


Criticisms of Radiometric Dating

The rate of radioactive decay is not constant and was faster when the Earth was young, therefore giving a false indication of old age.

For radiometric dating to be accurate, one has to know how much of the parent and daughter elements were present when the decaying started.

For radiometric dating to be accurate, one has to know how much of the parent and daughter elements either escaped or were added since the decaying started.

Since all matter was created at once, shouldn't everything have the same date?

Why are some radiometric dates so far off of what we know they should be, such as recent lava flows that give incredibly old dates.

The RATE project has assembled a group of scientists to investigate the accuracy of radioisotope dating.  They claim to have found evidence to disproving its accuracy and have produced the video Radioisotopes and the Age of the Earth based on these results.

Fossil wood found in ancient limestone (Hawkesbury Sandstone)


Answers to the criticisms

What is the evidence that decay rates have remained constant?

The stars provide an observable record of radioactive decay.

On several occasions, astronomers have been able to analyze the radiation produced by supernovas. In a supernova, the vast amount of energy released creates every known nuclide via atomic fusion and fission. Some of these nuclides are radioactive. We can detect the presence of the various nuclides by spectrographic analysis of the supernova's radiation. We can also detect the characteristic radiation signatures of radioactive decay in those nuclides. We can use that information to calculate the half-lives of those nuclides. In every case where this has been done, the measured radiation intensity and the calculated half-life of the nuclide from the supernova matches extremely well with measurements of that nuclide made here on Earth.Now, because light travels at a fixed rate (a bit under 300,000 kilometers per second), and because stars are so far away, when we look at a distant star we're seeing it as it was when that light left it and headed this way. When we look at a star in the Andromeda Galaxy, 2,700,000 light-years away, we're seeing that star as it was 2,700,000 years ago. And when we look at a supernova in the Andromeda Galaxy, 2,700,000 years old, we see nuclides with the exact same half-lives as we see here on Earth. Not just one or two nuclides, but many. For these measurements to all be consistently wrong in exactly the same way, most scientists feel, is beyond the realm of possibility.

It has been shown that slight changes in decay rate are possible.  And it may even be be possible that yet unknown mechanisms have changed the decay rates.  However, this would have severe consequences.  Every time an isotope decays into its daughter element a certain amount of heat is released.  If the decay rate increases, the same total heat is released, just over a shorter period of time.  Right now, this heat keeps the Earth's core molten.  Otherwise the Earth would have cooled billions of years ago.  In fact, before nuclear energy was understood, Lord Kelvin calculated that the Earth would have cooled in a only few hundred million years (he, of course, didn't know about nuclear heating in the core).  If the decay rate had increased by the amount suggested by the Young Earth Creationists, then the heat released would almost certainly have evaporated the Earth.  While it is possible that the decay rates have not been perfectly constant, even changes of a few percent would have dire consequences for the Earth.  To imagine that it is off by a factor of 450,000 as required by the claims of the Young Earth Creationists is about as improbable as something can get.


How can we know how much of the parent and daughter elements were present when the decaying started?

U-235 and U-238 provide a means to verify the assumption of how much of the parent and daughter elements the sample started with.  

  • Uranium's daughter element is lead.  Common lead contains a mixture of four isotopes.  Since the proportions of the lead isotopes are very nearly constant, lead-204, which is not produced by radioactive decay, can be used to accurately estimate the original quantities of lead-206 and lead-207.  This provides an accurate estimate of the original daughter element..
  • U-235 and U-238 have different half-lives.  The comparison of the dates a sample gives using each of these elements provides further evidence that the initial assumptions were correct for this sample.

Potassium-Argon dating - Argon does not react chemically, so any found inside a rock is very likely the result of radioactive decay of potassium.


The most accurate test of the assumptions about the starting parent and daughter elements is to date the sample using multiple methods.  Since the dating methods use different parent and daughter elements, it is highly unlikely that the sample could be contaminated in a way that would affect the different methods in such a way as to all give the same wrong date.  Matching dates provide strong evidence that the initial assumptions were correct.

The following applies to minerals.  It does not apply to some of the other techniques, such as Carbon-14 dating.

Minerals form by recognized chemical processes that depend on the chemical activity of the elements involved. The chemical behavior of an element depends on its size and the number of electrons in its outer shell. This is the foundation of the periodic table of the elements, a basic part of chemistry that has stood without challenge for a hundred and fifty years. 

The shell structure depends only on the number of electrons the nuclide has, which is the same as the number of protons in its nucleus. So the shell structure doesn't change between different nuclides of the same element. K39 is chemically identical to K40; the only way we can distinguish between them is to use a nonchemical technique like mass spectrometry. (Note: It's true that some natural processes favor some isotopes over others. Water molecules containing oxygen-16 are lighter and therefore evaporate faster than water molecules with oxygen-18. However, as far as is known such fractionation occurs only with light nuclides: oxygen, hydrogen, carbon. The atoms used in radiometric dating techniques are mainly heavy atoms, so we can still use the axiom that mineral-forming processes can't distinguish between different nuclides.)

So the processes that are involved in mineral formation can't distinguish between nuclides. Sr86 atoms and Sr87 atoms behave identically when they bond with other atoms to form a mineral molecule. If there are ten Sr86 atoms for every Sr87 atom in the original magma melt, there will be ten Sr86 atoms for every Sr87 atom in the minerals that crystallize from that melt. 

Isochron dating does not even require knowing the starting amounts, thus eliminating this criticism altogether.

Why are some radiometric dates different from what they should be, such as recent lava flows that give incredibly old dates.

I dropped my watch in water and it stopped, so I went to store to purchase another.  As I looked at the watches on display, I noticed that while most kept good time, some were many hours off.  Behind the counter was a man repairing watches.  Apparently some watches consistently give the wrong time.  Water immersion had caused my watch to not work at all.  I realized I had no choice - I immediately left the store without a new watch.  After all, I had just proved that watches can't keep time!

I've got 100 watches.  Ninety-nine give the same time, one is wrong.  Does that prove that watches can't keep time?

That's the criticism in a nutshell.  Radiometric dating occasionally doesn't work, therefore it must not work at all.  This is clearly absurd.

Certainly radiometric dating has its limitations.  There are known conditions that will induce error in the dating, such as contamination and leaching.  Sometimes it's possible to tell in advance when a specimen can't be dated properly, other times it's not.  Consequently, some samples are going to give false dates.  It's just a fact of life.  Just like medical tests that sometimes give false positives.  Does this mean the test is worthless, or does it simply mean it has limitations and should be used with caution?  Detroit makes millions of cars each year.  Some of those cars are lemons.  Do a few lemons prove that Detroit can't make cars?   Geologist will tell you to cross check dates with other dating methods to verify that it's not a lemon.  But the vast majority of radiometrically dated samples give accurate and consistent dates.  The exceptions don't mean that the method is invalid, just that it's not perfect and a little common sense should be used.

See a detailed example of some failed Mt. St Helens lava datings and an explanation of why they failed (with diagrams)

Creationists sometimes take advantage of the known conditions that will produce false dates.  They will gather samples that meet the conditions known to produce false dates and then hold it up as "proof" that radiometric dating doesn't work.  See Radioisotopes and the Age of The Earth for examples of this.

My sister was just diagnosed with thyroid cancer. When she told me the treatment for her type of cancer has a 97% cure rate, at first I was relieved. Then I realized, hey it fails 3% of the time! Worse yet, those “doctors/scientists” can’t even always explain why it fails. What kind of faulty science is that? If real world factors cause it to occasionally fail, then clearly this treatment is useless and totally invalid. Especially since they can’t even always explain why it failed. How can they truthfully believe that this cancer treatment works? When they claim that it works, they’re just ignoring all the times it doesn’t work.

I’ve also decided to start playing baseball again. I played for the base team when I was in the service, but I was never a very good hitter. Ted Williams has a book on hitting tips. I thought he’d be a good person to get some tips from. Then I found out his batting average was only .344! Clearly his batting method doesn’t work! I mean, after all, if his method occasionally fails, than it can’t be valid – wouldn’t you agree? When he claims he can hit a baseball, he’s just blatantly ignoring all the times he struck out.

Someone needs to call Detroit. They claim they know how to make cars. But clearly this is not the case. After all, sometimes cars come off the assembly line defective. Just because the vast majority of them run, that doesn’t give them the right to claim their manufacturing methods work!

And don’t get me started on radiometric dating. It might be true that it has been shown to provide accurate and consistent results most of time. It even gives correct results when compared with non-radiometric dating methods.  But, every once in a while, real-world factors such as contamination and leakage cause invalid results.
Scientists even admit that sometimes they can’t explain why a particular sample failed to date properly. Sometimes all the samples from a given area give weird results.
So when they claim radiometric dating works, they’re just basing that on the thousands of times it worked and ignoring those occasional failures. How bogus is that?

It’s a good thing places like AiG are there to provide a fair balanced view of this critical issue.

Want to learn more?


Carbon-14 Dating

Since it has a relatively short half life of 5,730 years, it is used to date relatively recent items, usually less than 40,000 years.

Carbon-14 (C-14) is a radioactive isotope of carbon-12. Carbon-14 is continuously created by cosmic rays bombarding nitrogen in the upper atmosphere. The atmospheric carbon dioxide (CO2) contains this C-14.  Living organisms then acquire carbon from carbon dioxide while they are living.  When the organism dies, the C-14 begins to decay into nitrogen-14.  The proportion of carbon-14 remaining give an indication of how long ago it died.

While the rate of creation of C-14 appears to be roughly constant, there are factors that affect it..  Volcanic eruption, or other events that give off large amounts of carbon dioxide, can reduce local concentrations of C-14.  The ratio of C14 has also been reduced by a few percent due to the release carbon dioxide by industry. It is also affected by solar wind and the earth's magnetic field.  These factors are known to affect the accuracy by as much as 5%.

Critics of C-14 dating make much of the difference in C-14/C-12 ratios across time.  However, they usually conveniently fail to mention that these factors only affect the date by a few percent.  An item dated as 30,000 years old would be off by only 1 - 2,000 years due to changes in C-14 ratios.   Also, much research has been done to determine the past values for this ratio.  Numerous items whose dates are historically know have been C-14 dated with excellent results.  See Accuracy for examples of these.


Viewer Feedback

2006-01-15 Anonymous (Atheistic Evolutionist) wrote
Interesting, Factual, Biased to Evolution

2006-01-31 Anonymous (Young Earth Creationist) wrote
Articles were very helpful, much of which i agree. seems we all have a strawman or two in our worldview closet. if only we would get them out and discuss with charity over a cup of java. maybe without caffiene of course. looking forward to any response on RATE's trace C14 in diamonds and other 'carbon dead' artifacts. What is seems strange is they are selective as to what rates are accelerated ie certain decay rates but others and diffusion rates seem to be unaffected? Perhaps we all have faulty bricks in our houses and even some that we still have put any motar on as of yet.
also although you have a lot of good links from all sides, you may want to add www.c14dating.com unless i missed it. thanks

epicidiot reply: Thanks for the link.  I have added it.  I am working on a response to trace C-14 problems.  It should be ready soon.  I'm always interested in online civil and intellectual discussions of theses issues.  I'm also happy to add well-written rebuttals to my web pages.

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