googlef87758e9b6df9bec.html A Sure Word: The Dating Game: How Old Ages Are Assigned to Rocks

Sunday, June 8, 2008

The Dating Game: How Old Ages Are Assigned to Rocks

During old fashioned revivals, red-faced preachers have often said that some people are more interested in the ages of rock than the Rock of Ages. I guess that’s true to a point but some people believe that there are rocks that are billions of years old. We need to be able to address this and not simply sweep it under the rug as if we’re not concerned with it. If the old dates are correct, it’s direct evidence against a young earth. This undermines the clear reading of Genesis. Then how do scientists date rocks? There are actually several methods. We’ll discuss a few here and also point out some of the flaws in those methods.

First, some rocks are assigned ages based on which fossils are found in them. If you find fossils of trilobites, for example, then scientists will assume the rocks around it are approximately 300 million years old. That’s because they believe trilobites lived 300 million years ago. However, this is a dangerous form of circular reasoning. Consider this hypothetical discussion:

Evolution Scientist: “Those rocks are 65 million years old.”
Creation Scientist: “How do you know that?”
ES: “Because they have dinosaur fossils in them and dinosaurs lived 65 million years ago.”
CS: “How do you know dinosaurs lived 65 million years ago?”
ES: “Because they’re found in rocks that are 65 million years old!”

So we see dating rocks according to the fossils in them assumes the dates assigned to the fossils are correct.

Another method of dating rocks is radiometric dating. Rocks contain unstable isotopes such as uranium and potassium. Over time, these unstable isotopes decay and turn into stable isotopes (uranium decays into lead and potassium decays into argon). The decay rate can be very slow and is measured in terms of half-lives. When a rock of unknown origin is found, scientists can measure the ratio of uranium/lead, for example. Then, they can calculate how long it would take for that ratio to be reached and that becomes the age assigned to the rock.

However, there are a few assumptions that make radiometric dating suspect:

1) It must be assumed that decay rate has always been constant (not faster or slower in the past).

2) We must assume that the beginning ratio of parent element/daughter element was 100/0 – that is, there could be no daughter element present at the forming of the rock.

3) It assumes an entirely closed system. None of the parent element could have leeched out of the rock and none of the daughter element could have entered in.

If any of these assumptions are shown wrong, this entire method of dating is proven unreliable. Is there a way to see if these assumptions are valid? Actually there is!

Dr. Steven Austin, a young-earth creationist and PhD geologist, tested (via potassium/argon testing) some of the rocks formed during the Mt. St. Helens eruption to see what dates the samples would yield. His samples were only a few years old, yet yielded ages between 350,000 and 2.8 million years old! (source here). Needless to say, this is strong evidence against the reliability of radiometric dating. If rocks of known ages cannot be dated correctly with these methods, how can we put any faith in the dates of rocks of unknown origin?

Still another method of dating is radiocarbon dating. Similar to radiometric dating, radiocarbon dating can only be used on organic substances. Carbon-14 (C14) is an unstable isotope found in all living organisms. Once the animal dies, C14 decays into C12. By measuring the C14/ C12 ratio, we supposedly can estimate how long ago the animal lived.

But radiocarbon dating has its own shortcomings. C14 has a very short half-life, only 5730 years. This means that after about 60,000 years, there should be no C14 left in organic material. Scientists estimate diamonds to be millions or even billions of years old. However, recently the RATE project found detectable amounts of C14 in 12 samples of diamonds. The only conclusion is that diamonds cannot be millions or billions of years old for there should be no C14 left in them!

There’s a lot more that could be said about dating rocks. I’m sure I’ll touch on some of these tangent issues in future blogs. However, the fact of the matter is clear: the current methods scientists use to date rocks are riddled with difficulties. How they can use them with a straight face remains the harder question!


NP said...

Firstly, your presentation of index fossils is rather disingenuous. You are implying that the dating of layers based on their fauna was done by simply presuming the ages according to when the fossilized organisms were supposed to have lived. But the fact is that the rocks in which they have been found have been dated using radiometric dating. Your problem hence is with that of induction, i.e. it would be akin to arguing that not all copper wires conduct electricity just because some do.

Secondly, your reservations with radiometric dating are quite unreasonable. The claim that the known decay rates of isotopes were not always constant is both unfounded and hypocritical. Unfounded because you have no evidence, theoretical or otherwise to demonstrate that the laws governing nuclear physics were different in the past. Hypocritical because young earth creationists often will claim that things like the erosion caused by Niagara Falls, the salinity of the ocean, etc - which are clearly variable - place an upper limit on the age of the earth. The second assumption is not as unrealistic as you may think - take the example of K-Ar dating. Argon is a volatile gas, and so would not otherwise be found in sediments.

You mention that radiometric dating can be incorrect if the system is not closed, but this is not news to scientists. Ironically, you go on to give supposed disproofs of the accuracy of radiometric dating by giving examples where it clearly isn't a closed system. That is simply disingenuous.

Now, given the possibility that isotopes can leach into a sample, scientists can work around this. Firstly, they can recognize instances in which it is more likely for exogenous isotopes to contaminate a sample. Secondly, the problem can be overcome by using multiple independent dating methods to verify that they are providing consistent results. This eliminates the supposed unreliability of radiometric dating.

Let me just add that even IF radiometric dating was wholly incorrect, creationists STILL have to account for the faunal progression in the fossil record. Prior to the advent of radiometric dating, the relative ages of each layer could be determined by applying the basic principles of superposition, i.e. in places where there is no folding or faulting, older strata will be deeper to younger strata. And the progression of life forms is observable in these strata. You are trying to downplay the use of index fossils, but the fact remains that trilobites still have not been found in Pleistocene rocks, nor are there fossilized lagomorphs in the Pre-Cambrian.

Anonymous said...

why do people have such a problem even imagining that there could possibly be God?If He could do anything and everything, don't you think he could alter the laws of decay as well? I know this is a "scientific" debate but might I intervine and point out, that "o what faith ... That this world and the universe were created by mere accident and accretion.. O what faith you have. For it is much more convincible that everything was created by a god who loves us. O what a meaningless life you hold. A being of selection over time must surley have no hope in life. Live to live. Then die. What pain you must suffer. Why have ethics? Why have meaning? For you have found your life in this world. I choose more. Enjoy your debates. Let peace keep their peace." "this is the virdict: light has come into the world, but men loved darkness instead of light because their deeds were evil. Everyone who does evil hates the light, and will not come into the light for fear that his deeds will be exposed. But whoever lives by the truth comes into the light, so that it may be seen plainly that what he has done has been done through God" john 3:19