From Clay in Clyde, OH
I have a friend who is a young-earther, and one of his reasons for doubting carbon dating methods is he believes radiation levels changed at the time of the flood, which he views as global. I've read several articles on your site about carbon dating but haven't found an answer to this idea. Is such a thing possible, even if you considered the flood to be global?
In a word, no. You will find a detailed response to this challenge to an old earth in my latest book, Navigating Genesis, particularly pages 111–13, 159–72. On pages 111-13, I explain how biblical texts like Genesis 2, Ecclesiastes 1, Jeremiah 33, Romans 8, and Revelation 21 rule out the possibility that any change has occurred in the laws of physics at any time in the history of the universe. Astronomical observations confirm this biblical declaration of unchanged physics, in some cases to 16 places of the decimal.
On pages 159–72, I address the implications of the changes in the physical laws that are required to sustain the family of global flood models undergirding young-earth creationism. For example, to make their global flood models work, young-earth creationists are forced to claim that certain radiometric decay rates were sped up by a factor of a billion times and that at least six thousand miles of lateral tectonic movement occurred within a five-month time span. However, such accelerated radiometric decay and tectonic activity would have killed all life on board the ark, and the earth today would look very different from what we see now.
As you probably noted from our web resources, carbon-14 decay is different from uranium and thorium decay in that its rate of decay does vary to a slight degree. Carbon-14 is produced in the atmosphere as cosmic rays strike nitrogen-14 atoms. It also is produced in Earth's crust when radioactive decay of uranium and thorium transforms nitrogen-14 into carbon-14. Because of small variations in the strength of the Sun and Earth's magnetic fields, the rate at which cosmic rays penetrate Earth's atmosphere varies slightly. These slight variations are recorded in the deep ice cores recovered from three sites in central Antarctica and four sites in Northern Greenland. Thus, physicists are able to accurately determine carbon-14 decay rates throughout the past 800,000 years. They find no evidence for a dramatically accelerated carbon-14 decay rate at any conceivable date for Noah's flood, nor do they find in the seven deep ice cores any evidence that a major flood inundated either Antarctica or Greenland.