Review by Greg Neyman
© Answers In Creation
First Published 23 July 2006
Radioisotope dating of rocks in the Grand Canyon is the title of a five page article in the June 2005 issue of Creation magazine. The author, Andrew Snelling, attempts to cast doubt upon the dating of rocks of the Grand Canyon. 1
As is typical of young earth articles, Snelling starts out with using some emotional appeals, speaking about the beauty of the Grand Canyon. This is not a surprise, since most young earth materiel relies more on emotion than it does on scientific facts. Snelling then goes on to mention the accepted radiometric dating ages for the basalt lavas located deep within the canyon. He lists the age as last having erupted about 1,745 million years ago, and they were metamorphosed about 1,700 years ago. He then states,
“They believe that when different radio-dating methods are used on the same rocks, they will all yield the same age.”
“They” refers to long-age geologists. Unfortunately for Snelling, this
statement is not true. Geologists know the limitations of radiometric
dating. They would prefer for the dates to all match perfectly, but
they know they will not. Hopefully, when dating is performed, it will
match close enough to the margin of error to be useful. Sometimes it
does, sometimes it doesn't. Such is the nature of radiometric dating.
As geologists, we do have trust that the science behind the dating is
accurate, but we also realize there are many influencing factors that can
change the outcome of the date.
Sometimes it is hard to tell which rocks young earth creationists obtained their samples from. In this case, we actually have a fairly good idea. In the basement of the Grand Canyon, there is a body of rock known as the Vishnu. This body of rock forms the bedrock in the canyon. Within the Vishnu, there is another body of rock known as the Brahma Schist. This apparently is the rocks from which Snelling obtained his samples, since he refers to them as Brahma amphibolites. According to the US Geological Survey website2, the Brahma is…
Consists of amphibolite, hornblende-biotite-plagioclase schist, biotite- plagioclase schist, orthoamphibole-bearing schist and gneiss, and metamorphosed sulfide deposits. Mafic to intermediate-composition metavolcanic rocks. About 1.75 billion years old. Locally interlayered with Rama Schist and Vishnu Schist.
Snelling dated amphibolites from the Brahma Schist.
Snelling Does His Own Dating
Snelling collected numerous samples of amphibolites during his raft trips through the Canyon. The sample size that Snelling dated is twenty-seven. Snelling sent the samples to two top dating laboratories. Typically, Snelling refuses to provide an estimated date to the laboratories (he does not operate like normal geologists do). This article does not say whether or not he provided the estimated dates.
Another issue that is difficult to examine is Snelling’s methods of sample preparation. Secular geologists, who routinely date rocks, know precisely how to prepare samples for dating. Snelling, who does not accept radiometric dating, has little practical experience in radiometric dating sample preparation. This article fails to explain how he prepared the samples. However, since he has an agenda (to disprove radiometric dating), it doesn’t matter if the samples are prepared properly or not.
It is not surprising that the ages that Snelling obtains does not match (if
they did, would he become an old earth creationist?). Snelling says,
“Clearly, the calculated ages are useless for dating any event.” Since
Snelling already believed this, he confirmed his own thoughts.
Snelling says that dates which don’t agree are the rule. I agree, and so would most geologists. Radiometric dating does rely on the assumption that decay rates are constant, and this truth has been borne out in many experiments. The variance comes in the amount of parent-daughter isotopes. There are factors which can influence the ratios one way or the other. These contaminants can throw dates off. That is where other methods can be used by geologists. For instance, a rock may give very different dates. The geologist would then look at the dates of the layers above and below…were these dates reliable? If so, they give some necessary information to help determine the most accurate date. They look at the environment…could contaminants leak into the rock samples…or isotopes leak out. We know that the dating of rocks is not perfect, but that does not stop geologists from trying to provide the most reliable date they can.
Snelling uses a text box at the end of the article to push the theory that radioactive decay in the past was accelerated. This is a recent, interesting development in the young earth movement. Young earth scientists now admit that the rock record contains evidence of billions of years of radioactive decay. I welcome this admission, because it makes the old earth creationist case even stronger.
The young earth model now states that two periods…the creation week, and the Genesis Flood, were responsible for this accelerated decay. In short, the problem this model faces is one of heat. Cramming billions of years of radioactive decay into a year long flood is a bad idea because the amount of heat from this amount of decay would have melted the entire earth. For those who wish to examine this theory in more detail, please check out the review of the young earth book, Thousands…Not Billions.
Yes, we already know that there are discordant isochron dates out there. Geologists who frequently date rocks run across this occasionally. They also run across dates which agree with each other. Snelling has merely confirmed what geologists have known for some time.
For More Reading
1 Creation Magazine, Volume 27, Issue 3. Published on the web at http://www.answersingenesis.org/creation/v27/i3/canyon.asp
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