The other day I was confronted with a question. What do you think about the knife that was found recently and dated to be millions of years old? Doesn’t that make you question the bible’s creation story? For me it doesn’t cause doubts because there are other reasonable arguments for god’s existence, like the evidence of objective moral truth or the evidence for intelligent design. This did however cause me to think about the evidential strength of dating objects to disprove creation and the age of the earth. In fact I knew nothing about radiometric dating and I must admit that learning about it seemed a bit intimidating. I am also sure that this intimidation is what leads most people to just accept this type scientific statements as fact instead of taking a critical look at the process. This lack of knowledge was also a bit exciting because I got to roll up my sleeves and learn something new. What I discovered was there are some key assumptions hidden in this research which makes some of the dates a little less concrete (pun intended) than you may be led to believe. My hope with this posting is that I can try and make a complex topic a little more simple to understand and point out some “faith” given to this process by some in the scientifc community. I also posted some links to the source material for my journey not only to credit those whom I have received this information from, but to allow you to dive in yourself if you wish to further your understanding of the topic.
It’s all about the Half Life:
The half-life is the time it takes for any quantity to fall to half its value as measured from the beginning of a given time period. Within the dating of ignaeous rocks or organic materials the quantity of material to be measured is radioacitve decay. To illustrate this take for example carbon dating of bones with C14, which has a half-life of 5,730 years. Once a living thing dies the isotope C14 will decay or emit radiation over time (more on this later). That is to say that when something dies and the amount of C14 in the bones is at fifty percent than 5,730 years have passed. In another 5,730 years the half value of that amount will have dissipated meaning only twenty five percent of the original amount will remain. After three half lives only twelve and a half percent and so on until there is no radioactive material left to measure. So a half-life is the amount of time it takes an isotope to decay or decrease by fifty percent.
Carbon C-14 Dating:
Carbon -14 dating is used to date dead organic matter like plants, animals, and humans. There are three naturally occurring varieties of carbon contained in living things, C12, C13, and C14. Of these Carbon 14 (C14) is used in dating because of the three, this is the isotope which is unstable and decays. This means that once something dies C 14 begins to decay and the half life cycle begins, C12 and C13 the other carbons found in organic matter are stable and do not decay. Organic matter, like us humans, plants, and animals have this carbon in our bodies because of the air we breathe and the plants and animals we eat. This C14 gets into our food and air when cosmic rays bombard the atmosphere, produce neutrons, and when these hit nitrogen they produce radioactive C14. When this C14 is combined with oxygen it becomes carbon dioxide and is consumed by plants and animals, which we eat.
When a living thing dies the intake of C14 ends and the half life begins. So how do we know how much C14 something started with? For this part of the equation scientist begin by measuring the C12, the stable carbon and relate it against how much C14 is still in the item. They then establish the half life based on this ratio. This is where we run into the first assumptions. The first assumption here are that the amount of C12 and C14 in the atmosphere have always been stable. That is to say that carbon in the atmosphere is the same now as six thousand years ago or even back to 1940 when Willard Libby developed this technique. The second assumption is that all things emit C14 at the same rate. Even if this assumption is correct Carbon dating with C14 will not allow dating past approximately seventy five thousand years because of its half-life.
Radiometric Dating of Rocks:
The most common radiometric dating of rocks is by dating Igneous rocks, these rocks are the result of lava and include rocks like granite. These rocks are used for dating because science believes that the clock starts on the half-life of these rocks when the lava cooled and formed them. As with carbon dating, dating igneous rock requires an isotope to decay over time that can be measured. In this case the isotope decays and turns into another isotope, this is called the parent daughter system. In the case of Granite Uranium-238 (the parent) will decay into Lead-206 (daughter). By determining the amount of parent and daughter isotopes present scientists assume that they can determine the age of the rock. This type of dating suffers from the same assumptions as carbon dating that; the initial condition of the rock’s isotopes are known, that isotopes decay at the same rate over time, and that external conditions did not change the rate of decay.
Assumptions on Initial Condition and rate of Decay have big Implications:
I will try to use an everyday example to illustrate the assumptions and how inaccurate they make the conclusions of dating rocks and carbon based objects. Say you found a car idling in your driveway and you wanted to know how long it had been sitting there. You look inside, see that the car has half a tank of gas, and you conclude that when a car with a full tank of gas is idling, it will deplete a half tank of gas in four hours. You therefore conclude that, the car has been idling in your driveway for four hours. We are making some pretty big assumption here aren’t we? We are assuming the gas tank was full when it arrived prior to us observing it, and that it was only idling during the time it was outside of our observation. What if it was parked just prior to you coming outside and when it was left it had a little over a half tank of gas? you just concluded that what was actually 2 minutes of the car idling in your driveway was four hours. Also, what if the car had a full tank but was parked in your driveway for 1 hour while someone pressed on the gas pedal, raising the RPM’s causing the car to burn gas at a faster rate? you are now off by three hours. This example although simple shows that by assuming the starting isotope variable and the rate of decay variable you can be off in estimations by well…. it appears millions of years.
RATE Group Findings:
The above example is further illustrated by the findings of the RATE group (Radioisotope and the Age of The Earth) . In 1997 a group or research scientists conducted a study to see if the variable assumptions outlined above and commonly used in radiometric dating are valid. To give you two examples the researchers took rock samples from Mount Saint Helens lava dome formed in 1986 and had it tested using the parent daughter method described above. The tests showed that the rock was 500,000 to 2.8 million years old even though it was known to only be 11 years old. The group also took rock samples from Mount Ngauruhoe eruptions of 1949, 1954, and 1975. When these rocks were tested they we’re reported to be dated between 270,000 and 3.5 million years old. These examples show two things, that when these rocks are formed they have a significant amount of daughter isotopes already in them, and the assumptions made with regard to dating rocks using the parent daughter method is unreliable.
How about them dinosaurs? Well I saved this for last because the dating of fossils uses a combination of the two methods. Fossil dating usually includes super positioning, which is testing the rocks above and below the fossil. They use the parent daughter isotope method to “correlate” the age of the fossil based on the age of the rocks around it. Carbon dating for fossils is generally only done when they believe that the organic remains are less than seventy five thousand years old. However, some fossils thought to be millions of years old have been tested using carbon dating and found to still contain amounts of C14. This may lead you to conclude that dinosaurs are less than seventy five thousand years old.
What the information shows is that the scientific methods used for carbon dating and radioisotope dating are not generally in dispute, what is questionable is the interpretation of past events and the starting variable of the radioisotopes. The bottom line is the science is fallible here and radiometric dating is far from direct evidence. It is certainly far from disproving a young earth. We must also keep in mind that when presuppositions drive scientific pursuits the data will always be compromised. My article has hopefully given you some good information from which to ask questions when new “evidence” arises with regard to the earth being millions of years old.
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