The assumptions used with carbon dating may explain the various conflicts in dating items. First, they assume that when the rock was formed only the parent element was present, and there was no daughter element. This is problematic because lead (daughter) is derived from uranium (parent). If it wasn’t present initially, then uranium in its purest form must have just suddenly appeared. Second, it is assumed that within any given sample, no parent or daughter elements ever entered or left the sample. Third, the rate of radioactive decay has remained constant. “Bad dates” are typically thrown out of the dating process.
Various factors affect the accuracy of radiometric measurements. The amount of cosmic rays resulting from the sun’s activity (with decreasing strength of the earth’s magnetic field) affects the production of carbon-14 (C14). The oceans are the largest carbon sinks on the planet, and when they covered 100% of the earth (global flood), instead of todays 70%, carbon levels were arguably different.
The half-life of C14 is 5,730 years, meaning half of the C14 will decay in that time and the rest in 50,000 years. C14 levels do not remain constant as assumed and requires calibration as far back as reliable historical data exists - about five thousand years. This correction converts “radiocarbon years” to “calendar years,” but beyond 5,000 years, the correction and resulting ages are left to guess work.
Future carbon dating will not be so reliable because fossil fuels have no C14 content and have diluted the C14 content over the last 100 years. On the other hand, atmospheric testing of nuclear weapons in the 1950s and 1960s increased C14 levels.
C14 is produced in the upper atmosphere when cosmic radiation interacts with nitrogen gas, converting nitrogen-14 to C14. These C14 atoms combine with oxygen to form carbon dioxide (CO2) gas, which is absorbed by plants. The plants use the carbon in the CO2 to make sugar and other food while animals eating the plants ingest the C14 (mixture of stable C12 and radioactive C14). At death, the C14 that it had slowly decays into nitrogen gas. One can date the specimen by measuring the amount of C14 left in the specimen. The problem is that no one knows how much C14 it began with.
Correction factors are necessary to get a reasonably accurate age. The problem is that the ratio of C14 to C12 changes, but is generally assumed the same today, as it was thousands of years ago.
Radiocarbon samples which obtain their carbon from a different source (or reservoir) than atmospheric carbon may yield what is termed apparent ages. A shellfish alive today in a lake within limestone catchments yields a radiocarbon date that is excessively old. The reason for this anomaly is that the limestone, which is weathered and dissolved into bicarbonate, has no radioactive carbon. Thus, it dilutes the activity of the lake meaning that the radioactivity is depleted in comparison to C14 activity elsewhere. The lake, in this case, has a different radiocarbon reservoir than that of the majority of the radiocarbon in the biosphere and therefore an accurate radiocarbon age requires that a correction be made to account for it.
The discovery of tropical fossils in arctic places implies a time when the Earth was warmer, which might have been the result of more CO2 (and therefore more C12) in the atmosphere. If there were more C12 in the atmosphere earlier than 5,000 years ago, then all radiocarbon dates would appear to be much older than actual calendar years.
The principal isotopes of carbon, which occur naturally, are C12, C13, (both stable) and C14 (unstable or radioactive). A given element is said to have different isotopes when it shares the same number of protons in each atom, but differs in neutron numbers. These isotopes are present in the following amounts C12 - 98.89%, C13 - 1.11% and C14 - 0.00000000010%. Thus, one C14 atom exists in nature for every one trillion C12 atoms in living material.
If the atmosphere is made up of 0.04% carbon dioxide, and one-trillionth of that CO2 is C14, then one trillionth of 0.04% of the gas molecules in the atmosphere contain C14.
Since the amount of carbon in the atmosphere is so small and the amount of C14 is just a small fraction of that, ratios involving carbon are very sensitive -- meaning very little change in the amount of C12 or C14 affects radiocarbon dating. Additionally, the fluctuations in atmospheric carbon levels over the past 5,000 years have made it necessary to come up with complex algorithms to convert radiocarbon years to calendar years. The fact that the C14 ratio is changing is proven by the need for correction factors to compensate for the changing ratio. The ratio of C14 to C12 has changed in the past, even before the industrial revolution.
The myth is that radiocarbon dating can accurately establish exact dates of the death of organic remains almost as far back as 50,000 years. The reality is that one would have to know the C14/C12 ratio in the environment at the time of the death of the sample. The fact is that we can only infer that ratio for the past 5,000 years or so using historical records. The inference is that the ratio changes sufficiently so that calibration factors have to be used to convert radiocarbon years to actual calendar years. Since the ratio is known to have changed in historic times, the scientific simply cannot assume it was constant before historic times.