SCIENCE & TECHNOLOGY
The Age of the Earth
Part 2: Radiometric Age Dating
By Steve Webb
Greetings in Christ! I am a Christian geologist who has been working in this field of science for 38 years. I take the Bible as the accurate inspired word of God, as I have done since my youth. As explained in a prior introductory blog, I believe the Earth is considerably older than 6000 years and I do not believe that this conflicts with Scripture. The immensity of this subject is more than book length. In fact it would require many books, particularly to explain to those with limited science backgrounds. Due to the fact that my time and energy for writing on this subject is limited, all I can do is bite off a single small piece of this at a time. You can either like what I say or reject it. In any case, there are not many areas that I can speak with true authority, but this is one of them. I know my geology. I hope you will give me audience.
The single topic that I am addressing in this short note is radiometric age-dating. I plan to do this in non-technical terms. There is no shortage of technical literature on this subject if you want to get into it, starting with the basics in Wikipedia. Radiometric age-dating (RAD) is based on the recognition that radioactive isotopes have measureable decay rates. There are hundreds of such isotopes that have been used for age-dating. RAD has been performed on isotopes with half-lives ranging from 10 years (tritium) to over a billion years (Samarium 147). This brings up the immediate question as to how someone could possibly postulate something in the range of millions or even billions of years when mankind hasn't even been around that long. The answer is simply by mathematical extrapolation. Decay rates are measured and extrapolated. There is no guesswork to it.
Young Earth Christians (YEC) have had a field day criticizing RAD on several fronts. One of these is the admitted assumption that RAD depends on constant decay rates. How do we know that radioactive decay rates have remained constant over time? The answer is that we don't. However, RAD does not stand on its own with respect to judging time passage. Astronomers would quickly jump into this discussion talking about how they have come to measure the speed of light and stellar distances independent of radiometric age-dating. But since I am not an astronomer I will say no more on that account. Instead I will say that I see geological processes at work for which reasonable time estimates can be made. These processes include sedimentation rates, erosions rates, precipitation rates, soil formation rates, and others. As but one example, limestone (a sub-specialty expertise of mine) has upper limits on the rate at which it can be deposited. This is because it is primarily a biologically deposited sediment that is dependent directly upon algal contribution along with variable contribution from other organisms. There is no way to speed up the deposition of this kind of rock beyond a certain upper limit. Flood waters won't increase it. Neither will cataclysmic events. When these kinds of processes are taken into account, a judgment can be made as to the passage of time. While it is impossible to accurately calibrate radiometric age-dating via this means of comparison, one can still get a sense of whether things seem reasonable. To be more specific, when I see a pile of sediments (typically thousands of feet thick) that have a large time difference between the top and the bottom as measured by RAD, I would likewise expect to see processes at work that have required considerable amounts of time. And I do. The processes are compatible with the RAD's both for long time spans and short time spans.
Another area where YEC's have criticized RAD, and I have heard sermons on this since my youth, is by pointing out the many things that can and do gone wrong with it. Are they right? Can huge errors be made in RAD? Of course they can! There can be errors due to contamination, insufficient sample, poorly calibrated instruments, technician error, incorrect isotope choice, poor collecting techniques, and other reasons. They can also be abused by people intentionally trying to discredit them, which I have sadly witnessed. But if such error is possible, why should we trust it? My reply is: Why should we trust any kind of testing? Why should we rely on blood tests, water purity tests, air quality tests, toxicology tests, DNA tests, along with hundreds of other tests? They are prone to the exact same kinds of errors. I personally had a blood test one time that came back with a very strange chemical imbalance. Upon further testing and sleuthing, it turned out that the vehicle that transported my blood had lost its air-conditioning and the sample became overheated, causing erroneous results. If I had accepted the test results at face value I would have undergone unnecessary medical treatment.
So knowing that test results can be erroneous for any kind of testing, what do we do about it? A number of things: 1) We check for repeatability, 2) We cross-check against other methods, and 3) We check for reasonableness. In RAD if we don't achieve repeatability, the data is not accepted. It doesn't matter whether or not this lack of repeatability is clearly understood, it is just too risky to trust the data. In RAD we also usually have the luxury of being able to cross-check one RAD method against another RAD method. It is a powerful means of determining the level of confidence.
With respect to reasonableness, results need to make sense laterally, taking into account geologic variation along the same horizontal strata, and vertically, comparing strata above with strata below. By analogy, if you fill your compost bin year after year with dirt and leaves, the compost at the bottom will be older than that at the top. This is the same principle with sedimentary rock. There are cases in geology where this natural ordering is distorted but they are rare and easily recognized. In other words, if RAD dates do not progressively show younger dates in a stratigraphically upward direction (and I have never personally seen an exception), they would fail the test of reasonability.
I think many Christians perceive RAD as a means by which evil scientists are trying to disprove the Bible. This is furthest from the minds of the people for which I work. We are just trying to piece together the geology and this is a powerful tool that has proven itself in solving practical problems particularly in oil and mineral exploration. It would be discarded in a heartbeat (as have other methods) if it had not proven itself. There are many more pages that I could write on this subject but I am intentionally trying to keep this short and readable for the average reader. I pray that you will consider the things that I have said. Blessings and keep the faith!
Please note, as a ministry, GotQuestions.org officially holds to Young Earth Creationism. We truly and fully believe that Young Earth Creationism best fits with the biblical account of creation. However, we recognize that Old Earth Creationism is a valid viewpoint that a Christian can hold. In no sense is Old Earth Creationism heresy and in no sense should Old Earth Creationists be shunned as not being brothers and sisters in Christ. We thought it would be worthwhile to have some articles that positively present Old Earth Creationism, as it is always good for our viewpoints to be challenged, motivating us to further search the Scriptures to make sure our beliefs are biblically sound.
Image credit: Antelope Canyon by Jean Edmonds; All rights reserved
Age of the Earth: The SeriesPart 1: Introduction
Part 2: Radiometric Age-Dating
Part 3: Dinosaurs
Part 4: Tree Rings
Part 5: The Meaning of Yom
Part 6: Other Scriptural Difficulties
Part 7: Noah's Flood
Part 8: Hebrew-Judaeo Worldview
Part 9: Who were the Cavemen?
Part 10: The Garden of Eden
Part 11: Bible Genealogies
Tags: Controversial-Issues | Science-Creation
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