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.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.The New Zealand curve is representative for the Southern Hemisphere, the Austrian curve is representative for the Northern Hemisphere. This makes it possible to tell the age of substances that contain carbon. Dates obtained are usually written as before present ('present' is 1950).Atmospheric nuclear weapon tests almost doubled the concentration of Radiocarbon dating, also known as the C14 dating method, is a way of telling how old an object is. Plants take up atmospheric carbon dioxide by photosynthesis, and are eaten by animals, so every living thing is constantly exchanging carbon-14 with its environment as long as it lives. In 1958 Hessel de Vries showed that the concentration of carbon-14 in the atmosphere varies with time and locality.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.
However, conditions may have been different in the past and could have influenced the rate of decay or formation of radioactive elements.
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.
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.