How accurate are carbon-dating methods? All methods of radioactive dating rely on three assumptions that may not necessarily be true:

1. Rate of Decay

It is assumed that the rate of decay has remained constant over time. This assumption is backed by numerous scientific studies and is relatively sound. However, conditions may have been different in the past and could have influenced the rate of decay or formation of radioactive elements. 

Evolutionists assume that the rate of cosmic bombardment of the atmosphere has always remained constant and that the rate of decay has remained constant. Scientists place great faith in this dating method, and yet more than 50% of radiocarbon dates from geological and archaeological samples of northeastern North America have been deemed unacceptable after investigation.ⁱ

While there is no proof that the rates were different in the past than they are today, there is also no proof that they were the same. Thus radioactive dating relies purely on assumptions. We could put forward the following counter arguments to the constancy of these assumptions:

a) The constancy of cosmic ray bombardment might be questioned. The current high rate of entry might be a consequence of a disturbed post-Flood environment that altered the carbon-14 to carbon-12 ratio. Pre-Flood dates would thus have to be discarded.

b) An increase in the magnetic field of the earth would have shielded the earth from cosmic rays. Some scientists argue that the magnetic field of the earth has declined over time.

c) Atmospheric carbon forms just 0.0005% of the current carbon reservoir—99.66% of the earth's carbon exists in limestone, 0.31% in oil and gas, and 0.02% in coal. Carbon-14 comes from nitrogen and is independent of the carbon-12 reservoir. If even a small percentage of the limestone deposits were still in the form of living marine organisms at the time of the Flood, then the small amount of carbon-14 would have mixed with a much larger carbon-12 reservoir, thus resulting in a drastically reduced ratio. Specimens would then look much older than they actually are.

d) Even if the rate of decay is constant, without knowledge of the exact ratio of carbon-12 to carbon-14in the initial sample, the dating technique is subject to question.

2. Clock Reset

It's assumed that the clock was set to zero when the study material was formed. This requires that only the parent isotope be initially present or that the amount of daughter isotope present at the beginning is known so that it can be subtracted.

Many examples from literature show that the zero-reset assumption is not always valid. Volcanic ejecta of Mount Rangitoto (Auckland, New Zealand) was found to have a potassium-40 age of 485,000 years, yet trees buried within the volcanic material were dated with the carbon-14 method to be less than 300 years old.ⁱⁱ 

A further example from a lava flow off the coast of Hawaii shows similar discrepancies. If dated with the carbon-14 method, the flow appears to be less than 17,000 years old, but dating with the potassium argon method gives dates of 160,000 to 43 million years. A rock sample from Nigeria was dated at 95 million years by the potassium-argon method, 750 million years by the uranium-helium method, and less than 30 million years by the fission-track method.ⁱⁱⁱ

If the clock is not set to zero when a deposit forms, then there can be no starting point from which to calculate the age of a deposit. 

3. Closed System

It is assumed that we are dealing with a closed system—no loss of either parent or daughter elements has occurred since the study material formed.

No scientist can guarantee that any sample can be considered a closed system unless it was isolated from its environment when it was formed. Elements can be transported into a sample or leach out of a sample.

Scientists will reject theories about the age of the earth that do not conform to the norm. They will argue that the clock was not reset if the age is too old, or that isotopes were selectively removed if the age turns out to be too young. In the study on the Hawaii lava flow cited above, it was argued that entrapment of excessive amounts of argon gas had made the samples appear older than they were.

Radiometric dating techniques are thus based on sound scientific principles, but rely on so many basic assumptions that Bible believers need not have their faith shattered by data derived from these techniques. What do rock layers on the Earth's crust tell us about our origins and the age of the earth?

For more on this subject, see the video Bones in Stones. Updated January 2009. 

ii A. McDougall Polach and J.J. Stipp, "Excess Radiogenic Argon in Young Subaerial Basalts From Auckland Volcanic Field, New Zealand," Geochemica et Cosmochemica Acta 33 (1969): 1485-1520.

iii E. Fisher, "Excess Rare Gases in a Subaerial Basalt from Nigeria," Nature 232 (1971): 60-61.