Welcome! I can totally relate to what you’re talking about, as I’ve heard that one all my growing up years. As an adult I was surprised to find out Carbon-14 wasn’t the only dating method considering how often it was dissed in YEC materials.
I’m sure the more science-minded users here will have better resources, but here’s one that I appreciated in response to some of Kent Hovind’s arguments, since those are ones I grew up hearing:
“Carbon dating” is one of the most misused terms when used outside of science. No one carbon dates a rock because rocks aren’t valid samples for carbon dating. The limit for carbon dating is about 50,000 years, so if you hear someone say that carbon dating returned a date of 10 million years then they are getting something really, really wrong.
Carbon dating can only accurately date organic material from the past 50,000 years, or so. Carbon-14 (14C) is continually made in the upper atmosphere as cosmic rays and other high energy particles bombard Nitrogen-14. Plants take up 14C in the form of carbon dioxide and make sugars from it. Herbivores eat the sugars in the plants, and carnivores eat the herbivores. Therefore, all terrestrial life has about the same 14C content in their bodies as that found in the air. When those organisms die they stop the turnover of 14C in their bodies. The 14C slowly decays over time, and we can determine how long ago something died by how much 14C is left. Since the half-life of 14C is only 5,700 years it can only be used over a relatively short span of time. It is also worth noting that aquatic life can derive its carbon from dissolved stores in lakes and oceans which have a different percentage of 14C than the atmosphere does.
One of the keys to 14C dating is historic levels of 14C in the atmosphere. The production of 14C can change, so dates have to be calibrated to these historic values. Luckily, there are known annual deposits that contain either atmospheric carbon or organisms which allows this type of calibration. Such records include ice layers, tree rings, and lake varves. Here is a graph showing the relationship between uncalibrated 14C age and the actual age of these objects:
As you can see, the actual age drifts slightly from the 1:1 line, and this is the calibration that is added to 14C dates.
The other source of possible error is contamination. If older carbon from the environment works its way into your sample then it will date older than it should. One way to check this is look at the overall carbon isotope makeup of your sample. Photosynthesis tends to favor the ligher isotope of carbon which is 12C. Therefore, if your sample is organic and not contaminated by inorganic carbon from the environment then it should be rich in 12C compared to inorganic sources of carbon.
Long story short, 14C dating can be accurate within a limited time span if done properly with carefully selected samples. In other words, it is just like the rest of science. It is a very reliable technique when done correctly.
Thank you for this insight. So, if C-14 only works for about 50000 years, what methods are being used to date the earth, fossil record, etc?
Thanks!
Wow. So much I didn’t know. Thankful for your analysis and information.
Rubidium-Strontium is one that comes to mind just off the top of my head for billions of years … but there are bunches more. I have a feeling you’re about to hear from some here who are much more knowledgeable than I am about it. So I’ll defer for the moment and watch the responses myself.
I will describe the general methods, but keep in mind that there are always exceptions. I am not a geologist, so this is stuff I have picked up over the years. If there are any mistakes I encourage any geologists to correct them. With that said . . .
Most of those techniques date igneous rocks (i.e. rocks that form from cooling molten lava) using other radioactive elements with longer half lives. One example is U/Pb dating of zircons. Uranium decays through a whole chain of intermediates until it reaches Lead which doesn’t decay, so these are the elements that are measured for the age of the zircon. The reason zircons are used is that when they crystalize from molten lava they exclude Pb and include U in their crystals. This is due to the difference in charge between U and Pb. Therefore, when a zircon forms it has no Pb in it, but it does have U. Another cool feature is that there are two U isotopes that have different half lives. 238U decays to 206Pb with a half life of 4.47 billion years and 235U decays to 207Pb with a half life of 710 million years. If you date a zircon using both decay chains and they produce the same age then you have extra confidence that the date is correct.
The other common dating techniques are K/Ar and Rb/Sr if you want to google them.
Just one note. Geologists don’t directly measure the age of fossils. Instead, they date the igneous rocks around the fossils, be it in the layers where the fossil is found or the layers above and below the fossil.
Hi Austin, welcome!
This article explains all the main dating methods used in geology, including a section on radiometric dating, with all the different elements that can be tested for. The neat thing is that different dating methods can often be used to cross-check a proposed date. It isn’t quite the guesswork and wishful thinking operation that YEC sources make it sound like. It’s math.
A great book on the age of the earth written by a couple of Christian Geologists is The Bible, Rocks and Time: Geological Evidence for the Age of the Earth. In includes a discussion of radiometric dating of rocks in chapters 14 and 15 that covers the various methods.
For an example of how radiometric dates can be cross checked read this article by Joel Duff Smoking Gun Evidence of an Ancient Earth. His site is full of articles that refute the YEC position.
Here is a link to thread that links some great articles comparing lake varves, tree rings, and carbon dating. The ASA article has some good graphics charting the comparison, which is tough to argue against.
Here is the graphic, showing how stuff you can look at and count (tree rings and layers in a lake) overlap and correspond to carbon dating.
BioLogos has a lot of resources aimed at non-scientists. Look in the resources section for videos on the science behind evolutIon.
This link talks about dating methods:
https://biologos.org/resources/audio-visual/how-old-is-the-earth
Carbon-14 dating only works for organic objects up to 50,000 years old. It compares the ratio of 14C to 12C found in today’s atmosphere to the ratio in the object to be dated. While alive, a living thing has the same ratio of 14C to 12C as in the air. The C12 is stable, but the C14 decays to C12 once the tree or animal dies with a
half-life of 5,000 years. so that an object 5,000 years old would have 1/2 of the original C14, 10,000 years old would have half of that, or 1/4, and so on.
Of course, we don’t know if the amount of
C14 in the air has always been the same, but objects from Egypt and tree rings an with known ages have allowed us to calibrate C14 dating very accurately back 10,000 years. The amount of C14 in air fluctuates a little, but not by orders of magnitude, so that objects measured at 20,000 years are not really less than 6,ooo years old. Some of the Geiger counters used in the 1950s were not very accurate, a fact pounced on by YEC’s at the time, but modern means of measuring C14 are very accurate and more sensitive.
Some YEC’s asked if the earth is billions of years old, why do we have any C14 left. The answer is that C14 is continuously formed when cosmic rays hit the upper atmosphere.
Thank you all very much. This is incredibly helpful and reassuring!
It’s this type of data that I have yet to see YEC’s really explain, specifically the lake varve data. I have seen YEC’s try to claim that a flood could create the varves, but how could a flood sort leaves and insects by their 14C/12C ratios? If the leaves and insects in these varves were alive when the flood happened then why shouldn’t they all have the same 14C/12C ratios? Moreover, why would the 14C/12C dates for the lake varves also overlap with the same data from tree rings and ice layers (we could add speleothems to the list if we wanted).
Also, apologies if this is a repeat but @jammycakes has written some excellent pieces on this topic in particular. I don’t have a link to his other blog but found this writeup that covers many of the same ideas:
Ten things you need to know about the age of the earth » james mckay dot net
Here is Jammycakes other blog. Good stuff.
That is quite a competitive field!
An internet search of dating methods is probably a bad idea.
Dr. Roger C. Weins is a Christian, but also a PhD Physicist with a specialty in radiometric dating methods and has done work for Caltech and the Los Alamos National Laboratory. Dr. Wiens has written an excellent paper designed to provide an overview of the different dating methods to Christians which brings the science down to the layperson level.
Excellent article, I had read it years ago, but still one of the best at explaining things.
Forgive me if this was mentioned by someone else earlier. There is now an updated “tree-ring, varve, carbon-14” paper based on a whole new round of C14 measurements in Lake Suigetsu. The paper includes a step-by-step demonstration of why we can be confident in the conventional understanding of tree-ring growth, varve formation, and carbon-14 production and decay. The paper also includes descriptions of the methods YEC employ for the purpose of creating doubt. The paper will become open access to non-ASA members after January. If you aren’t a member, or don’t know a member, you can email me at davidson@olemiss.edu and I can send you a pdf (please do not post it or send it to friends before January).
Davidson, G. and K. Wolgemuth (2018) Testing and verifying old age evidence: Lake Suigetsu varves, tree rings, and carbon-14. Perspectives on Science and Christian Faith , 70(2):75-89.
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