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The fatal flaw with radioactive dating methods


Published: 30 July 2009 (GMT+10)
This is the pre-publication version which was subsequently revised to appear in Creation 32(1):20–21.
scientific dating

Many people assume that the dates scientists quote of millions of years are as reliable as our knowledge of the structure of the atom or nuclear power. And radioactive dating is so shrouded with mystery that many don’t even try to understand how the method works; they just believe it must be right.

But the basic concept of radioactive dating, sometimes called radiometric dating, is not difficult, especially since all of us regularly calculate how much time has passed: for example, since our birth, or since we started on a walk. A swimming race is a familiar situation that illustrates the simple principles involved in measuring time. Once we understand what we actually need to do we can apply the same principles to radioactive dating, and see if the methods do what they are claimed to do.

Picture a swimmer competing in a 1,500 metre race and an observer with an accurate wristwatch. We note that at the instant the swimmer touches the end of the pool our wristwatch reads 7:41 and 53 seconds. How long has the competitor taken to swim the race?

When I have asked an audience this question they have looked at me incredulously and said, “Starting time?” They realize that you cannot know how long the swimmer took unless you knew the time on the wristwatch when the race started. Keep that in mind when you think about working out the age of something. Without knowing the starting time it is impossible to establish the time for the race. Note: Impossible.

Actually, knowing the starting time is still not enough. During the race you have to watch the swimmer and count how many laps he has swum so you know that he has done 1,500 metres. And you have to check to make sure he touches the end for each lap. Without these observations you cannot be sure that the time is valid. That is why you need three timekeepers to independently record the times during the race to meet the standard needed to enter the record books.

Would it make any difference if the watch we were using was more accurate? Absolutely not! You could talk about the tiny quartz crystal and the piezoelectric effect used to provide a stable time base for the electronic movement. You could describe the atomic workings of the quartz oscillator and how it resonates at a specific and highly stable frequency, and how this is used to accurately pace a timekeeping mechanism.

The fact is that you can only establish the time for the race if it was timed by two or more reliable eyewitnesses who observed the start, the progress and the finish of the race.

This illustrates the problem with the radioactive dating of geological events. Those who promote the reliability of the method spend a lot of time impressing you with the technical details of radioactive decay, half-lives, mass-spectroscopes, etc. But they don’t discuss the basic flaw in the method: you cannot determine the age of a rock using radioactive dating because no-one was present to measure the radioactive elements when the rock formed and no-one monitored the way those elements changed over its entire geological history.

The educational page hosted by the US Geological Society provides one recent example of the way radioactive dating is explained to the public. They focus on the technicalities of radioactive decay, etc. but don’t even mention the fact that we can’t measure the concentrations of isotopes in the past.

So, the fatal problem with all radioactive dates is that they are all based on assumptions about the past. You can get any date you like depending on the assumptions you make. And that is what geologists do—they make up an assumed geological history for rock after the event, depending on the numbers that come from the geochronology lab that measures the isotopes in the rocks now. Dating secrets explains how this works in practice. Some real-life examples of how geologists change their assumptions after the event include the dating of Skull KNM-ER 1470 (see The pigs took it all) and of the Mungo skeletal remains, Australia (see The dating game).

Next time you see dates quoted of millions of years remember that the numbers are not scientific measurements of time elapsed. They are the result of big philosophical assumptions.

Helpful Resources

Readers’ comments

Mason S.
Rob's right. If you know how far something traveled and the rate at which it traveled then you can find how long it took.

distance = rate x time

With radiometric dating we're instead looking to find the time (or age.) The formula would look like this:

time = distance / rate

So far they've been able to prove that the rate of decay is a constant so we've got one variable.

Next they're able to observe how decayed it is so they know the "distance" and have the final variable.

The answer is a little bit of math away.

And sure people will shout about the inaccuracies of radiometric dating but in every case I've found it's been the fault of the geologist/scientist/whoever and not with the process

Tas Walker
Hi Mason,
Sure, if you knew all that information about your rock sample you could calculate the time. But have you ever thought about where you would get that information from, since you can't travel back in time to measure it?
M. M.
Hahaha Rob, dont try to be a smartass when you dont know nothing about the metaphor in the depth.. How can you compare your wisdom to geological timing? -.- yeah, you got trolled by the author, And God bless you author for this wonderful article.
Narindra R.
As far as I know, secular scientists have it all wrong with C14 dating because they don't take in account the Divine Flood, which engulfed billions of tons of trees and changed drastically the C14/C12 coefficient.
Kim B.
As a swimmer myself, I can say you are correct. In fact, only a week ago I swam in a 1500 metre event, where my first 100 metres was eight seconds faster than my second. I would have been perfectly happy to have an assumption of my final time deduced from the time for that first 100 metres. Two minutes makes a massive difference overall!
Rob S.
Your statement “Without knowing the starting time it is impossible to establish the time for the race” is false. If you know the pool’s length and the swimmer’s speed, you can calculate the time for the race. You absolutely do NOT have to know the starting time.

In mathematics the formula is: distance = rate x time

Given the distance and the rate, you can calculate the time. Knowing the end point gives you the start point and the total time.
Tas Walker
So, Rob, how do you measure the swimmer’s speed?

Rob S. replies:

Take two observable points, measure the distance between them and the time it takes to swim them, and calculate the rate (r = d/t). Again, absolutely no reference to the race’s starting point is needed.

Tas Walker responds OK, Rob, so you measure the swimmer's speed over the last 10 metres of the race. Are you telling me that he has been swimming at that speed for the whole race? And how do you know how many lengths of the pool he has swum?

Unless you watched the race from the beginning you would not have a clue as to how many laps he has swum or how long he took.

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