Ten things you need to know about the age of the earth

Now as I keep saying, my position on the whole creation and evolution debate is simple.

Make sure that your facts are straight.

Genesis 1-11 is a part of the Bible that leaves a lot open to interpretation, and while it may seem audacious and bold and uncompromising and full of faith to opt for the most radical interpretation (a Literal Six Day Young Earth Creation, non-evolution, dinosaurs on Noah’s Ark etc), if you’re supporting this position with demonstrable falsehoods and displays of ignorance, you won’t be upholding the Bible; on the contrary, you’ll be undermining it.

Unfortunately, I frequently see well-meaning but badly informed Christians making claims about the age of the earth, and about how it is determined, that are demonstrably and indisputably untrue. Some of these are just rumours and hearsay, and some of them just demonstrate ignorance, but there is also a lot of misinformation out there being published by certain people with PhDs who should know better.

So before you rush into the debate with all guns blazing, here are ten things that you need to know about the age of the earth, the ages of rock strata, and how they are determined.

1. It is based on measurement and mathematics, not on guessing or presupposition.

I sometimes hear people claiming that determining the age of the earth is “guessing at best,” or that if you looked at the evidence with different, young-earth “glasses,” you’d get different, young-earth results. Or that old-earth results are based entirely on an a priori commitment to the theory of evolution and philosophical naturalism.

This is nonsense. The age of the earth is determined first and foremost by measuring things. Measuring and guessing are complete polar opposites, and measuring anything gives the same result no matter what “glasses” you look at it through. You could look at Mount Everest with glasses that make it look like it’s just four inches high all you like, but that won’t stop you from getting a height of 8,848 metres when you actually measure it.

Anyone who tells you that rocks don’t come with time stamps doesn’t know what they’re talking about. Rocks contain radioactive elements such as uranium-238, potassium-40, rubidium-87 and so on, which decay exponentially at well-established rates. When a rock cools below a certain temperature (the “closure temperature”), these elements are “locked in” in ways that follow certain highly predictable patterns. Scientists can then take samples from the rocks, measure their composition, determine how much these patterns have changed, and in that way determine the age of the rock.

You may have heard that radiometric dating has to make assumptions about the original composition of the rocks — how much of the “parent” and “daughter” isotopes were originally present. This is not true. There is a technique called isochron dating which avoids this assumption altogether. By taking multiple samples from the rock, you can plot a graph of 87Rb/86Sr against 87Sr/86Sr: its slope will give the age of the rock without having to know anything about its original composition. If there has been any contamination or leakage, the points on the graph will not lie on a straight line.

2. Its assumptions can be — and are — rigorously tested.

The claim that “historical science” relies on assumptions that can’t be tested because nobody was there to check (the “were you there?” argument) is simply not true. Historical assumptions can easily be tested by cross-checking different dating methods whose assumptions are independent of each other.

One particularly spectacular example comes from measuring rates of continental drift. In places such as the Hawaiian islands, the dates of lava flows increase linearly with distance from the hot spot in the earth’s crust over which the various islands have formed. In recent years, it has also become possible to measure continental drift directly using GPS. Everywhere we look, the measurements are exactly the same within the measured range of errors.

I’ve occasionally seen claims that different methods only give the same results because they make the same assumptions of uniform rates, or because they adopt the same worldview. This is patent nonsense. The whole point of cross-checks is to test assumptions, not to make them. In any case, any alternative explanation in which the rates weren’t constant would need to have something affecting all the different measurements in exactly the same way, in exactly the same proportions, in exact lock-step with each other, by a factor of up to a million. Since the different rates include nuclear decay, continental drift, formation of tree rings, lake varves, ice core layers, coral growth and a whole lot of other things as well, such a proposition is quite frankly preposterous.

3. Its reliability is measured and calculated as well.

The scientific consensus is that the age of the earth is 4.54 ± 0.05 billion years.

Note the second part of that figure — ±0.05 billion years. It indicates an uncertainty of just one percent. It means that scientists have a 95% confidence that the age of the earth is no younger than 4.49 billion years and no older than 4.59 billion years. Uncertainties fall away exponentially as you move away from the centre of the range, and the chance that the error could be even three or four times as big as that figure is so low as to be effectively zero.

Error bars and uncertainties are not guesses either. They are determined by taking multiple measurements and calculating a statistical property called the standard error of the mean — a precisely defined quantity derived from the “spread” of the results about their average value. There are similar formulae for how to calculate uncertainties when calculating the slope of a graph.

This figure also takes into account the confidence levels that scientists have that rates such as nuclear half lives are constant. They do not blindly assume that these quantities never changed in the past; on the contrary, they study the evidence to determine limits to how much these quantities could have varied over billions of years. These limits are plugged into their formulae.

The end result gives an error of just one percent. Your car’s speedometer is less accurate than that. And six thousand years falls so far outside of this error range as to be ridiculous.

For what it’s worth, the fact that its uncertainty is known contradicts the claims of some YECs that old-earth ages merely arise from old-earth presuppositions designed to make space for evolution. There is no possible way whatsoever of starting off with vague, non-specific “old-earth presuppositions” and ending up with a final result that is constrained to within just one percent.

4. Much of the evidence comes from the oil industry.

Jonathan Baker, a Christian geochronologist and author of the Age of Rocks blog, explains this quite clearly in his article, “Can Young Earth Creationists Find Oil?” As he explains, oil companies need to know both the ages of the oil deposits and their geothermal history. Too young, or too cool, and the deposits will be “premature” — still solid, and impossible to get out of the ground. Too old, or too warm, and they will have been baked into oblivion.

There is no way that petroleum geologists could be artificially inflating the ages of oil deposits and rock strata in order to accommodate an evolutionary worldview. They are paid to produce results that are correct, not results that are ideologically convenient. If their measurements really were ideologically motivated in that way, oil companies would waste a fortune (and a lot of political good will) drilling in all the wrong places, the geologists would be fired and spend the rest of their working lives flipping burgers in McDonald’s, and the radiometric labs would be sued out of their insurances.

5. There is no circular reasoning involved.

The claim that “fossils are used to date rocks and rocks are used to date fossils” is so misleading that it is, to all intents and purposes, a flat-out lie. Rocks that are used to date fossils are dated first and foremost by radiometric dating. Index fossils are then only used to date rocks that can not be dated radiometrically. There is nothing circular about that.

Similarly, claims that nuclear decay rates are determined from known ages of rocks are also misleading. This would only suggest circular reasoning if this were the only way that these rates were determined. It is not.

Reasoning is only circular if you have two different lines of evidence that both depend entirely on each other. In every claim of supposedly circular reasoning that I have seen, there have been other independent lines of evidence involved which haven’t been mentioned that break the circularity.

6. Fewer than 10% of radiometric results are “bad.”

There is a vast difference between “doesn’t always work” and “never works.”

Young earth organisations love to point out cases where radiometric dating didn’t work — for example, when different methods gave wildly different, or otherwise apparently wrong, results. However, if radiometric dating really were a chaotic mess that couldn’t distinguish between thousands and billions of years, these “bad dates” would be ubiquitous, while close agreement between different dating methods would be all but non-existent.

This is not the case.

Dr. G. Brent Dalrymple, one of the foremost experts on radiometric dating, estimates that no more than 5-10% of radiometric results are “bad.” In other words, more than ninety percent of the time, there is no disagreement; the resultant dates are as expected; and different dating methods do indeed give the same result.

Anomalous dates are not unexpected, and usually indicate that the rocks in question had a complex geothermal history, being heated sufficiently at one point or another to partly reset their “clocks.” However, far from demonstrating that radiometric dating never works, the fact that these cases are the exception rather than the rule demonstrates that 90% of the time, it works just fine.

In any case, there are over forty different isotopes used in radiometric dating, and each will work for some kinds of samples but not others — again, cross-checks between different methods tell us which is which. The fact that carbon-14 does not work on traffic cones, for example, does not prove that uranium-238 does not work on zircon crystals in granites.

Furthermore, the disagreements between different radiometric dates catalogued by the RATE project differed by up to about twenty percent. Disagreements of just twenty percent in a minority of results do not justify claims that all dating methods are systematically in error by a factor of up to a million.

7. Radiometric dating is expensive.

The number of samples that have been dated by multiple methods, with no surprises and with an agreement to within one percent or better, to ages far in excess of six thousand years, runs into the hundreds of thousands. Each sample costs as much as a small car to collect, store, process, and analyse in order to determine a date.

If “evolutionists” really were “throwing out dates that don’t fit their preconceived notions,” millions of results costing hundreds of billions of dollars in total must have been discarded over the past sixty years or so.

Why are there no accountants and bean counters creating a stink about this colossal amount of money being thrown away on wholescale scientific fraud? Given the number of young-earth creationists in the US Congress, why are none of them proposing the simple fix to the problem of requiring pre-registration of all radiometric studies? And why is there nothing about it on Wikileaks?

8. There are no reliable findings of primordial radiocarbon in ancient coals and diamonds.

The RATE project, a young-earth creationist research project that ran from 1997 to 2005, claimed to have found carbon-14 in ancient coals and diamonds that by rights should not have contained any.

Their work was reviewed by Kirk Bertsche, an evangelical Christian radiocarbon expert, who pointed out that not only were the amounts of radiocarbon very low, they also showed clear patterns that were characteristic of contamination. For example, the amount of radiocarbon in heavily processed samples was found to be much higher than those that had undergone comparatively little processing.

Furthermore, he pointed out that although they did attempt to take contamination into account, they did not follow the correct procedures for doing so. High-end radiocarbon laboratories go to extreme measures to avoid contamination, even so far as operating in specially constructed buildings with shielding against cosmic rays. The RATE team merely subtracted a “standard background.”

Contamination in carbon-14 dating is well studied and its vectors are well known. Before ancient samples can be demonstrated to contain primordial radiocarbon, contamination must be rigorously eliminated. To date, no finding of primordial radiocarbon in ancient coals and diamonds has adequately done so.

9. Young-earth “evidences” are based on low-precision measurements and unrealistic assumptions.

Consider the amount of salt in the sea — quoted by Answers in Genesis as one of their ten best evidences for a young earth. A number of things are immediately obvious.

  • It is based on rates that are extraordinarily difficult to measure, requiring massive international surveys.
  • No error bars in the measurements are quoted; only a vague hand-waving claim about being “generous to uniformitarians.” The error bars would almost certainly be large — well above ±10% for many of the different factors involved.
  • It is based on rates that can not realistically have been the same in the past as they are today, even in a “uniformitarian” model.

When up to date, accurate figures are used and everything is taken into account, a state of equilibrium — where the long-term amount of salt leaving the sea is the same as the amount entering it — is well within the range of experimental error. In fact, there is no evidence that the seas really are getting saltier with time.

Now compare that to radiometric dating.

  • It only requires a relatively small number of measurements (a few dozen) from each rock formation.
  • The error bars in both the measurements and the final result are a fraction of ±1% or better, and are always quoted.
  • It is based on rates that can not realistically have varied in the past without proposing radical new laws of physics for which there is no evidence whatsoever.

The amount of salt in the sea may be only one “evidence” for a young earth, but it is far from unique. Most of the “evidences” are vague at best about exactly what upper limit they place on the age of the earth, and in some cases don’t place any upper limit on the age of the earth at all. On the other hand, old-earth studies tend to be high precision, and the limits they place on the ages of the samples that they test are tight. The underlying assumptions are very, very reliable, for the simple reason that…

10. Accelerated nuclear decay is science fiction.

Perhaps the most outlandish claim that I’ve ever seen coming from the young earth movement is the RATE project’s hypothesis that nuclear decay rates must have been a billion times higher at certain points in the past six thousand years: notably during the first two days of Creation Week and during Noah’s Flood.

What makes this one so outlandish is that they themselves admitted that this would have released enough heat to raise the temperature of the earth’s surface to 22,000˚C — nearly four times that of the surface of the sun. Not only would there have been no Flood left, there would have been nothing left to be flooded!

On top of that, they acknowledged that no known thermodynamic process could have removed this amount of heat fast enough, and that any cooling process would also have had to have cooled rocks such as granites much faster than water, otherwise the oceans would have frozen over.

You can read all this in chapter 10 of the RATE project’s technical report, on pages 758-765.

The RATE team’s ability to downplay the seriousness of this problem is astonishing. Despite their own admission of an impasse of extraordinary proportions, the project has been portrayed as a success, with conferences, books and videos hailing it as providing conclusive evidence for a young earth, and accelerated nuclear decay being presented in their rebuttals of radiometric dating as if it were a proven fact. Randy Isaac of the American Scientific Affiliation (the US equivalent of Christians in Science) describes this portrayal as dishonest, and it’s not hard to see why.

Scientists do not blindly assume that radioactive decay rates are constant. Evidence for this comes from several different directions, not least the numerous cross-checks that are regularly done between radiometric dating and non-radiometric methods such as ice cores, lake varves, tree rings, Milankovitch cycles, and a whole lot more.

In any case, accelerated nuclear decay is the kind of discovery that would win a Nobel Prize if it could be shown to have any merit. Claims of this nature need to be supported by an extraordinary amount of evidence. A single set of studies by a single team working with a predefined agenda, that have never been replicated or even published in a mainstream peer reviewed journal, simply isn’t anywhere near sufficient.


For anyone wishing to discuss science and faith, there are plenty of interesting points for discussion out there, such as the apparent fine tuning that’s evident in the universe. The fact too that there are many questions about physics to which we don’t have the answers should also give us pause for thought, and perhaps instil humility in us as we marvel at God’s creation. But we don’t do ourselves any favours by claiming that scientists don’t know things that they do, or that they are just making things up when they are not, or that they are always changing their minds when they are not, or that they can’t test their assumptions when they can. Nor do we do ourselves any favours by getting all gung-ho and rushing headlong into the debate with all guns blazing only to prove that we haven’t a clue what we are talking about. Proverbs 19:2 says, “It is not good to have zeal without knowledge, nor to be hasty and miss the way.” In our discussions about these matters, let us be wise as serpents and innocent as doves.

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