Refuting “Radiometric Dating Methods Makes Untenable Assumptions!”
A very common claim of young earth creationists in trying to reject the evidence for an old earth is to loudly proclaim that radiometric dating methods “makes assumptions” and that these “assumptions” are somehow fatally flawed or not supported by evidence. These claims generally land in three different categories: (1) radiometric dating assumes that initial conditions (concentrations of mother and daughter nuclei) are known, (2) radiometric dating assumes that rocks are closed systems and (3) radiometric dating assumes that decay rates are constant. Most young earth creationists reject all of these points. As a scientific skeptics, we ask ourselves: is this really the case? Let us critically examine each of these claims and see if they hold up against the science. While doing so, we will have to learn about how radiometric dating actually works.
There are many different kinds of radiometric dating and not all conclusions we will reach can be extrapolated to all methods used. Also, different radiometric dating techniques independently converges with each other and with other dating techniques such as dendrochronology, layers in sediment, growth rings on corals, rhythmic layering of ice in glaciers, magnetostratigraphy, fission tracks and many other methods. This serves as strong evidence for the reliability of radiometric dating methods.
1. How does radiometric dating work?
A lot of atoms are stable. Some are not. There exists different versions, or isotopes of many elements. These isotopes differ in the number of neutrons they have in their nuclei. Those isotopes that are not stable decay into daughter nuclei. Those that did the decaying are called parent nuclei. If you have a rock that contains radioactive isotopes, these will decay over time. As time goes on, the ratio of the parent to daughter nuclei will change and decrease (as more parent nuclei decay into daughter nuclei, the former decreases and the latter increases). Measuring this ratio gives us an idea of how long ago the rock formed.
But wait a second! Doesn’t this assume that the rocks are closed systems? Surely, if some daughter nuclei left the rock or parent nuclei entered the rock, the dates would come out all wrong! While this is technically true, there are several mini-industries dedicated developing methods and techniques to make sure that there is no contamination and check to see if the rocks where disturbed between forming and being tested by scientists. How is this done? Let’s find out!
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2. Radiometric dating and testing for contamination and disturbances
On of the great things about many forms of radiometric dating is that they are self-checking. That is, you can see if the sample comes from rocks that have been disturbed (or contaminated) or not just by looking at the results. Now, creationists will claim that scientists are just somehow assuming that if samples show an age that does not fit their preconceptions, the sample must be contaminated or leaky. This is false. To see why, we need to look deeper into radiometric dating methods. A very important tool in radiometric dating is the so called isochron diagram and it holds the key to refuting the central creationist claims about radiometric dating.
One of the most beneficial things about it is that it can check itself for accuracy; the method tells you how well the rocks have been closed systems. An isochron diagram is obtained by looking at many minerals from the same rock or from rocks forming from the same parent mineral. Data is plotted on a simple two dimensional graph; the parent isotope on the x-axis and the daughter isotope on the y-axis. Both of these are divided or normalized by a stable isotope of the same elements as the daughter element. So on the x-axis, we have parent/(another stable isotope of the same element as the daughter) and on the y-axis we have daughter/(another stable isotope of the same element as the daughter).
If the samples have been undisturbed closed systems since formation, the data will fall on the same line (the isochron from which the diagram is named). The slope of this line is a function of the age of the rock. If the rock is older, the slope is higher. The reason scientists normalize with another stable isotope of the same element as the daughter is because most chemical or physical processes that occurs normally in nature does not differentiate between different isotopes of the same element when the difference in mass is as small as it is between isotopes of the same element that is used in radiometric dating. This means that the while different rocks contain different absolute amounts of the two isotopes, the ratio is same. At the time of formation for a rock, the isotopes for an element are homogenized and so the composition of a certain isotope is the same in all the minerals in the rock. But what happens when the rocks have been disturbed?
If a rock is heated during its lifetime, the system gets disturbed and some of the parent and/or daughter isotopes may move in or out of the rock. If so, the data will not fall on an isochron line, but will be all over the place. This tells scientists that the sample has been disturbed and cannot be dated with this particular method. So far from rejecting samples because they do not fit a preconceived notion of what the age should be, scientists reject samples because there is ample evidence that it has been disturbed: the data points do not lie on the isochron lines.
Scientists do not assume that rocks have been closed systems; it is a well-supported conclusion from experiments. But what about assuming that initial amounts are known?
3. Radiometric dating and initial conditions
A second property of isochron diagrams is that it actually gives the initial amount of daughter isotope as a result of the method. It is just the y-intercept of the isochron line. At this intersect, the ratio of parent/(another stable isotope of the same element as the daughter) is by definition 0 and so no amount of the daughter here is produced by decay of the parent in the rock. The initial conditions are just read off the graph; it is not just assumed.
4. Radiometric dating and decay rates
In a last ditch effort, young earth creationists exclaim that scientists just assume, without warrant, that decay rate are constant. However, this is not the case. Decay rates have been shown to be constant, despite very high pressure and temperature. Furthermore, by studying supernovas far away, scientist have determined that decay rates have been constant in the ancient past as well. Not only that, different radioactive isotopes decay differently and it is enormously improbable that a postulated difference in decay rates would affect all of them in the same way, yet as we have seen, different radiometric dating methods converge on the same date (within margins of error). Fourthly, decay rates can be predicted from first principles of physics. Any change would have to correspond to changes in basic physical constants. Any such change would affect different forms of decay differently, yet this has not been observed. As a final blow to the already nailed shut coffin of young earth creationism, had decay rates been high enough to be consistent with a young earth, the heat alone would have melt the earth.
5. Conclusion
Scientists do not assume that rocks have been closed systems, but they test for it. If all the data points fall on the isochron line, it has been a closed system; it it scatters, it has not and that rock is not used for dating with that method. Scientists also do not assumed that initial conditions are known; this is just read off the graph at the y-intercept. Finally, by studying supernovas, scientists know that decay rates have been constant in the past.
6. References and Further Reading
Dalrymple, G. B., (2004) Ancient Earth, Ancient Skies: The Age o the Earth and Its Cosmic Surroundings. Stanford: Stanford University Press.
Marshak, S., (2008). Earth: Portrait of a Planet. Third Edition. New York: W. W. Norton & Company.
Hedman, M. (2007). The Age of Everything. Chicago: University of Chicago Press.
Isaak, M. (2004). CF210: Constancy of Radioactive Decay Rates. Talk.Origins. http://www.talkorigins.org/indexcc/CF/CF210.html. Accessed 2011-08-12.
Isaak, M. (2004). CD001: Geochronometry and closed systems. http://www.talkorigins.org/indexcc/CD/CD001.html. Accessed 2011-08-12.
Isaak, M. (2004). Geochronology and initial conditions. http://www.talkorigins.org/indexcc/CD/CD002.html. Accessed 2011-08-12.
The reliability of percentage remaining (50% of the remaining rule) that has been used by scientists for the relative half-lives elapsed in responding to radiometric dating method is in question.
Refer to the right hand side of the table in the website address, http://en.wikipedia.org/wiki/Half-life. A list of percentage remaining that corresponds to the number of the relative half-lives elapsed are presented as follows:
No. of half –lives; Fraction remaining; Percentage remaining
0—————————–1/1————-100%
1—————————–1/2————-50% (=100% above x 50%)
2—————————–1/4————-25% (=50% as above x 50%)
3—————————–1/8————-12.5% (=25% as above x 50%)
———————–so on and so forth—————————–
n—————————–1/2^n———- (100%)/(2^n)
Using the above principle, we could arrive with weird and illogical conclusion below that would place the reliability of radiometric dating method into question:
If anyone of atoms, let’s say, atom A, has been selected from a parent isotope, let’s say, lutetium, to test the radioactive decay, this atom would surely have 50% of its atomic nucleus to be activated in radioactive decay in accordance to the 50% remaining rule as mentioned above. The rule has turned up to find favour in selecting an atom if one would examine the possible decay from parent isotope since it might not be possible if there would be more than one atom is selected as mentioned below:
If any two atoms, let’s say, atoms A and B, would be selected to test the decay, atom A might not respond to radioactive decay due to the existence of atom B in accordance to the 50% remaining rule. Or in other words, there would only be one atom responds to decay if there are two.
If any three atoms, let’s say, atoms A, B and C, would be selected to test the decay, atom A might not respond to radioactive decay due to the existence of atoms B and C in accordance to 50% remaining rule.
If any four atoms, let say, atoms A, B, C and D, would be selected to test the decay, atom A would have much lesser chance to respond to decay due to the existence of atoms B, C and D. There would turn up to have 2 atoms to respond if there are four as a result of 50% remaining rule is applied.
If there is a piece of 10,000 kg big rock[, let’s say, 10^(a billion) atoms], 50% of the big rock (turns up to be 0.5×10^(a billion) atoms would not activate in radioactive decay and these would cause the above four selected atoms, i.e. atoms A, B, C and D, to have even much lesser chance to respond to decay due to the possible present of many half lives in the future as a result of the existence of numerous atoms. As a result of the wide spread of the 50% inactive atoms within this piece of big rock, it is easily to destroy a piece a rock so as to locate a small portion that does not respond to decay due to it might need to wait for many half lives later in order to respond to decay as a result of the present of numerous atoms in accordance to 50% remaining rule. This is not true since scientists could anyhow pick up any rock, let’s say, lutetium, and yet still could locate decay emitted from it and this has placed 50% remaining rule into query.
If there is a gigantic mountain with 5,000 km height, 50% of this mountain would not respond to radioactive decay. This mountain certainly consists of a huge sum of atoms when huge volume is covered. As 50% of inactive atoms would have spread throughout the whole mountain as a result of 50% remaining rule applied, it would turn up that it would be easily to locate a small portion of rock from the mountain that would not respond to radioactive decay. However, that is not true when scientists would pick up any substance, let’s say, Carbon-14, from environments for examination since they could easily locate a small portion that would respond to decay. This has placed the reliability of 50% remaining rule into question as a result of the ease in locating a small portion of substance that would respond to decay despite its immense size.
The main problem here lies on scientists have placed 50% remaining rule on each half life and that half life is meant to be a very long years. For example, for Carbon-14, it would take 5730 years for the 50% of the initial remaining to turn up to lose its capability in radioactive decay in order to have 50% of what has remained after the initial remaining to activate radioactive dating. What if actual result of decay would not follow the sequence of 50% remaining rule in which it would take a shorter period to become inactive in decay instead of that 5730 years, using 5730 years as a base to presume that the decay would last in every half year would simply falsify the age that would be computed through radioactive dating method. What if the so-called, radioactive decay, would not cause any decay but it would restart its initial operation after numerous years later, the reliability of radiometric dating method is in question.
The following is the extract from the last paragraph that is located in the website address, http://www.askamathematician.com/2011/03/q-are-all-atoms-radioactive/:
[…But in general, the heavier something is, the shorter its half-life (it’s easier for stuff to tunnel out).]
The percentage remaining (50% of the remaining) to the responding to the number of half-lives elapsed contradicts the phrase, the heavier something is the shorter its half-life, as stated above. This is by virtue of the biggest the rock the heaviest it is and the biggest the rock the wide spread will be the 50% of the non-activation of nucleus to be in decay and it would lead to the longer the half-life due to the application of 50% remaining rule as spelt out above and this leads to the contradiction of the statement as stated in this website in which the heavier would lead to shorter half-life.
What if this 50% remaining rule as mentioned above would have applied to Carbon-14 (the Parent Isotope), the following condition would appear:
Years —————Half lives—Percentage Remaining
0———————-0———-100%
5730—————–1———-50% (100%*50%)
11460 (=5730*2)–2———-25% [50% (the above)*50%]
17190 (=5730*3)–3———-12.5% [25% (the above)*50%]
22920 (=5730*4)–4———-6.25% [25% (the above)*50%]
——————and so on and so forth—————————
4,500,000,000——837988—8^(-1)x10^(-251397)
Note that the above years have been computed up to 4.5 billion years due to the scientists suggest the age of the earth to be that.
From the 50% remaining rule that has been computed for Carbon-14 above, it could come to the conclusion that 50 atoms out of 100 would remain active in radioactive decay in 5730 years and the rest would turn up to have lost their value in radioactive decay. 25 atoms out of 100 would remain active in decay by 11460 years and the rest would turn up to have lost their decay. 12.5 atoms out of 100 would remain active in decay and the balance would turn up to have lost their decay by 17190 years. 6.25 atoms out of 100 would remain active in decay and leaving the balance to have lost their decay by 22920 years. 1 atom out of 8×10^(251397) would remain active in decay and the balance would have lost their capability in radioactive decay by 4.5 billion years. As 1 atom for Carbon-14 out of 8×10^(251397) would remain in active by 4.5 billion years in accordance to 50% remaining rule, it implies that it would need to get large amount of atoms from Carbon-14 so as to detect the existence of radioactive decay. This is not true in science since it is easily to locate Carbon-14 that would emit radioactive decay and this has put the reliability of 50% remaining rule into query.
Some might support that the 50% remaining rule is subjected to exponential progress. Let’s assume that what they say is correct and presume that the half lives for Carbon-14 in 4.5 billion years would be shortened by 80% as the result of exponential progress. The percentage remaining would turn up to be (100-80)%x8x10^(251397) and that is equal to 16×10^(251396). Or in other words, only 1 atom would respond to decay out of 16×10^(251396) and the rest of them should have turned up to have lost their value in decay. The ease to locate Carbon-14 that would respond to decay currently has put the reliability of radiometric dating method into question.
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Thanks for commenting!
No, it is not. The half-life is simply defined as the time period it takes for 50% of the remaining nucleotides to decay. The half-life can be, and has been, determined by careful experiments that conform with the models used.
You have misunderstood the basics of nuclear physics. Your view that an atom have multiple nucleus and that 50% of these decay after 1 half-life. This is not the case. You have a certain about of a certain radioactive substance. After 1 half-life, 50% of the nuclei of this substance have decayed. It is something that is the case for the population of all nuclei. It tells you nothing about a single atom.
When you test the decay rates, you do not select two atoms, you use a substance that contains billions and billions of atoms. You start at t = 0 and measure the number of nuclei N(0). Then, at a certain time = t afterwards, you measure the number of nuclei that have not decayed N(t). Then you plug those values into this formula:
N(t) = N(0) e^- lambda * t
This can be derived from simple facts by anyone with knowledge of differential and integral calculus.
No, that is not how it works. Eventually, all the radioactive nuclei in the mountain will decay. The probability does not refer to the probability that a single nuclei will decay (there are no “inactive nuclei”), but rather to how many of the nuclei will have decayed after one half-life.
We know from observing supernovae that the decay rate is constant over time. There is no escape.
Carbon-14 is not used to measure the age of the earth. Only substances with much longer half-lives are used for dating the age of the earth, such as radioactive forms of Rb (Rb-87), which has a half-life of 48 billion years.
This effectively destroys your position.
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