How Accurate Is Radiocarbon Dating?
Radiocarbon ages less than 3,500 years old are probably accurate. However, before accepting any radiocarbon date, one should know how the technique works, its limitations, and its assumptions. One limitation is that the radiocarbon technique dates only material that was once part of an animal or plant, such as bones, flesh, or wood. It cannot date rocks directly. To understand the other capabilities and limitations of radiocarbon dating, we must understand how it works and consider the flood.
Most carbon atoms weigh 12 atomic mass units. However, roughly one in a trillion carbon atoms weighs 14 atomic mass units. This carbon is called carbon-14—or radiocarbon, because it is radioactive. Half will decay in about 5,730 years to form nitrogen-14. Half of the remaining half will decay in another 5,730 years, and so on.
Two Sources. Carbon-14 comes from two sources: (1) the upper atmosphere where cosmic rays convert nitrogen-14 to about 21 pounds of carbon-14 per year, and (2) the earth’s crust where some neutron-heavy radioisotopes produce “cluster decay” by emitting small amounts of carbon-14 nuclei.3 The first source is widely known; few are aware of the second, which was discovered in 1984.
As explained in "The Origin of Earth’s Radioactivity" on pages 378–414, neutron-heavy and superheavy radio isotopes were produced in abundance during the flood, so when those isotopes escaped into the atmosphere and decayed, some unknown but significant quantity of carbon-14 was released. Smaller, but also unknown, amounts of carbon-14 are still escaping from the crust.4
Most carbon-14 in the atmosphere quickly combines with oxygen to form radioactive carbon dioxide. Plants can then take in carbon dioxide, incorporating in their tissues both carbon-14 (radioactive) and normal carbon-12 (non-radioactive) in the same proportion as was in the atmosphere at that time. Therefore, carbon-14 moves up the various food chains to enter animal tissue—again, in about the same ratio as carbon-14 had with carbon-12 in the atmosphere.
When a living thing dies, its radiocarbon loss (decay) is no longer replenished by intake, so its radiocarbon steadily decreases with a half-life of 5,730 years. If we knew the ratio of carbon-12 to carbon-14 in an organism when it died, we could date its death. The assumption usually made is that the atmospheric ratio of carbon-14 to carbon-12 has always been about what it is today—about one in a trillion—so every living thing died with that ratio of carbon-14 to carbon-12 in its tissues.5 However, that assumption will be shown (in a few pages) to be terribly wrong for organic material living before or soon after the flood.
The worldwide flood invalidated this standard assumption in a second way by uprooting and burying preflood forests. Less carbon was then in the biosphere to dilute the carbon-14 continually entering the atmosphere, so the ratio of carbon-14 to carbon-12 in the atmosphere sharply increased after the flood began, as shown by line B in Figure 248. If that ratio has doubled since the flood and we did not know it, radiocarbon ages of things that lived soon after the flood would appear to be one half-life (or 5,730 years) older than their true ages. If that ratio quadrupled, organic remains would appear 11,460 (2 × 5,730) years older, etc. Therefore, a “radiocarbon year” would not correspond to an actual year.
As explained in Figure 248, recent measurements show that the ratio of carbon-14 to carbon-12 has been building up in the atmosphere.6 However, for the last 3,500 years, the increase in the ratio has been slight but measurable.
Radiocarbon dating of vertical sequences of organic-rich layers at 714 locations worldwide has consistently shown a surprising result.7 Radiocarbon ages that are a few thousand years old do not increase steadily with depth, as one might expect. Instead, they increase at an accelerating rate. In other words, the concentration of carbon-14 is unexpectedly low in the lower organic layers and becomes more so the deeper the layer.
Figure 248: Increasing Amounts of Carbon-14. If one thought that the C-14/C-12 ratio had always been what it is today, one would incorrectly conclude that small amounts of carbon-14 in fossils meant that much time had passed. Instead, those organisms had less carbon-14 when they died.
Radiocarbon dating requires knowing the ratio of carbon-14 to carbon-12 in the atmosphere when the organic matter being dated was part of a living organism. The assumption (shown in red), which few realize is being made, is that this ratio has always been what it was before the Industrial Revolution—about one carbon-14 atom for every trillion carbon-12 atoms. Willard Libby, who received a Nobel Prize for developing this technique, conducted tests in 1950 that showed more carbon-14 forming than decaying. Therefore, the amount of carbon-14 and the ratio must be increasing. He ignored his test results, because he believed that the earth must be more than 20,000 –30,000 years old, in which case the amount of carbon-14 must have had time to reach equilibrium and be constant.6 In 1977, Melvin Cook did similar, but more precise, tests which showed that the ratio was definitely increasing, even faster than Libby’s test indicated.
Before the flood, about half the water on the earth today was under the earth’s crust, so the preflood earth had less sea area and more land and forest area. The small amount of carbon-14 that cosmic radiation produces in the upper atmosphere (about 21 pounds per year) was, therefore, diluted before the flood by the vast amounts of carbon-12 in the lush vegetation growing on the earth. That vegetation, buried during the flood, became our coal, oil, and methane deposits. The blue curve [line A] gradually rose from zero, because at the creation, cosmic radiation began producing carbon-14. During the flood [line B], some carbon-14 entered the atmosphere as radioactive decay products. (That is still is happening.1,2 ) Therefore, the ratio of carbon-14 to carbon-12 has steadily increased [line C] since the flood—but at a decreasing rate, because the more carbon-14 is in the atmosphere, more carbon-14 decays occur.
Tree-ring dating provides information on past concentrations of carbon-14 in the atmosphere. Some types of trees growing at high elevations with a steady supply of moisture will add only one ring each year. In other environments, multiple rings can be added in a year.8 A tree ring’s thickness depends on the tree’s growing conditions, which vary from year to year. Some rings may show frost or fire damage. By comparing sequences of ring thicknesses and ring damage in two different trees, a correspondence can sometimes be shown. Trees of the same species that simultaneously grew within a few hundred miles of each other may have similar patterns. Trees of different species or trees growing in different environments have less-similar patterns.
Claims are frequently made that these tree-ring thickness patterns of wood growing today can be matched up with those of some scattered pieces of dead wood, so that tree-ring counts can be extended back more than 8,600 years. This is incorrect. These claimed “long chronologies” begin with either living trees or dead wood that can be accurately dated by historical methods.9 This carries the chronology back perhaps 3,500 years. Then, the more questionable links are made based on the judgment of a tree-ring specialist. Sometimes “missing” rings are added.10 Each tree ring’s width varies greatly around the tree’s circumference. Standard statistical techniques could show how well the dozen supposedly overlapping tree-ring thickness patterns fit. However, in at least two instances tree-ring specialists have refused to subject their judgments to these statistical tests and would not release their data, so others could do these statistical tests.11
Several laboratories in the world are now equipped to perform a much improved radiocarbon dating procedure. Using atomic accelerators, a specimen’s carbon-14 atoms can now actually be counted, giving a more precise radiocarbon date with even smaller samples. The standard, but less accurate, radiocarbon dating technique counts only the rare disintegrations of carbon-14 atoms, which are sometimes confused with other types of disintegrations.
This new atomic accelerator technique has consistently detected carbon-14 in every organic specimen—even materials that evolutionists claim are millions of years old, such as coal and dinosaur bones.12 Small amounts are found so often among various specimens that contamination can probably be ruled out. Ancient human skeletons, when dated by this new “accelerator mass spectrometer” technique, give surprisingly recent dates. In one study of eleven sets of ancient human bones, all were dated at about 5,000 radiocarbon years or less! 13
Radiocarbon dating of supposedly very ancient bones should provide valuable information. Why are such tests rarely performed? Researchers naturally do not waste money on a technique that destroys their specimen and provides no specific age. In an organic specimen thought to be older than 100,000 radiocarbon years, all carbon-14 would have decayed, so an age could not be determined. Therefore, researchers will not radiocarbon date specimens they think are older than 100,000 years. Conversely, if carbon-14 is in any specimen, it must be less than 100,000 years old, even if the researcher believes the specimen is millions of years old.
PREDICTION 56: Bones or other organic remains that contain enough carbon and are believed to be older than 100,000 years will be shown to be relatively young in blind radiocarbon tests. Blind tests are explained on page 97. (This prediction, first published in the 6th edition (1995), p. 157, has now been confirmed.14)
Very precise measurements now show that most fossils—regardless of presumed “geologic age”—have roughly the same ratio of carbon-14 to carbon-12. (This includes fossil fuels: coal, oil, and methane.) Therefore, those organisms must have been living about the same time—and less than 100,000 years ago. Because almost all fossils are preserved in water deposited sediments, all this former life was probably buried in a recent, global flood.15
Radiocarbon dating is becoming increasingly important in interpreting the past. However, one must understand how it works and especially how the flood affected radiocarbon dating. Radiocarbon ages less than 3,500 years are probably accurate. Ages around 40,000 radiocarbon years, which are typical of coal, have much younger true dates—near the time of the flood, roughly 5,000 years ago. [See "When Was the Flood, the Exodus, and Creation?" on pages 482–484.]