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Is radiocarbon dating based on assumptions?

Combatting Misinformation with Facts

Unfortunately, a lot of misinformation about radiocarbon dating has been circulated by individuals who have neither training nor hands-on experience in this area. We feel a responsibility to make sure readers of this site go away with factual, truthful information, and this requires a frank correcting of some prevalent misinformation.

Assertion 1: Radiocarbon dates are based on the assumption that the atmospheric 14C to 12C ratio has been constant in the past.

This idea is advanced, for example, in The Young Earth:

but the assumption of the original concentration is once again the technique's Achilles' heel. (Morris, page 65.)
and in The Answers Book:

It is well known that the industrial revolution, with its burning of huge masses of coal, etc., has upset the natural carbon balance by releasing huge quantities of 12C into the air, for example. Tree-ring studies can tell us what the 14C/12C ratio was like before the industrial revolution, and all radiocarbon dating is made with this in mind. How do we know what the ratio was before then, though--say, thousands of years ago? It is assumed that the ratio has been constant for a very long time before the industrial revolution. Is this assumption correct (for on it hangs the whole validity of the system)? (Ham et al., page 68.)

The assertion that the "whole validity of the system" hangs on the assumption of a constant 14C/12C ratio in the past, or that this is "the technique's Achilles' heel" is incorrect. The whole validity of radiocarbon dating for the past 10,000 years---the time span of interest to biblical chronology---hangs only on the tree-ring chronologies which are used to calibrate it. (See How does the radiocarbon dating method work?.) This process does not involve any assumption about historic radiocarbon to stable carbon ratios because the radiocarbon concentration in the tree-ring samples would be affected in exactly the same way as the radiocarbon concentration in the specimen to be dated. Assertion 1 is false.

Assertion 2: Radiocarbon dates are based on the assumption that radioactive decay rates have been constant in the past.

To quote again from The Answers Book:

Some recent, though controversial, research has raised the interesting suggestion that c (the speed of light) has decreased in historical times. ... If it is correct, then radioactive decay rates would automatically be affected, and would show artifically high ages. (Ham et al., page 72.)

As with Assertion 1, Assertion 2 fails to account for the tree-ring calibration which is a routine part of modern radiocarbon dating. Although no convincing argument for a change in the speed of light over time has been made, the question is irrelevant to the validity of tree-ring calibrated radiocarbon dates. As with variation in atmospheric radiocarbon concentration, the decay rate of radiocarbon in tree-ring calibration samples would be affected in exactly the same way as the decay rate of radiocarbon in the specimen to be dated. Calibrated radiocarbon dates are immune to any supposed change in decay rate of radiocarbon. Assertion 2 is false.

Assertion 3: A pre-Flood vapor canopy would cause pre-Flood specimens to appear to be very old.

This idea is promoted in The Answers Book and other sources. It is based on the idea that a pre-Flood vapor canopy protected the earth's atmosphere from cosmic radiation and thereby caused a decrease in radiocarbon production. (See How does the radiocarbon dating method work?.) Something like a vapor canopy could affect the atmospheric radiocarbon concentration, but this fact is, once again, irrelevant to the validity of modern tree-ring calibrated radiocarbon dates. Assertion 3 is a special case of Assertion 1, and, like it, is false.

Assertion 4: The earth's magnetic field was stronger in the past, causing inflated ages.

This idea is similar to Assertion 3, but suggests instead that the cosmic radiation was shielded in the past by a stronger magnetic field of the earth. Again, the idea is that less cosmic radiation means less radiocarbon in the atmosphere, and less radiocarbon in the atmosphere means artificially old dates. Assertion 4, you can see, is another special case of Assertion 1, and similarly false.

  1. Ham, Ken; Andrew Snelling; and Carl Weiland. The Answers Book El Cajon, CA: Master Books, 1992.
  2. Morris, John D. The Young Earth Colorado Springs: Creation-Life Publishers, Inc. 1994.
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