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Internet Explorer is no longer supported. Try downloading another browser like Chrome or Firefox. If you already have an , in. The most well-known of all the radiometric dating methods is radiocarbon dating or carbon dating. Although many people think radiocarbon is used to date rocks, it is limited to dating things that contain carbon and were once alive fossils. So how does radiocarbon form? Cosmic rays from outer space are continually bombarding the upper atmosphere of the earth, producing fast-moving neutrons sub-atomic particles carrying no electric charge figure 1.
Figure 1. Since the atmosphere is composed of about 78 percent nitrogen, 2 a lot of radiocarbon atoms are produced—in total about These rapidly combine with oxygen atoms the second most abundant element in the atmosphere, at 21 percent to form carbon dioxide CO 2. Figure 2. Radiocarbon 14 C or carbon atoms combine with oxygen atoms in the atmosphere to form carbon dioxide CO 2 that circulates into the biosphere. Radiocarbon is thus incorporated into plants by photosynthesis and into the animals that eat the plants. Continued photosynthesis and feeding replaces the 14 C atoms lost from the plants and animals by decay back to 14 N nitrogen This carbon dioxide, now radioactive with carbon, is otherwise chemically indistinguishable from the normal carbon dioxide in the atmosphere, which is slightly lighter because it contains normal carbon Radioactive and non-radioactive carbon dioxide mix throughout the atmosphere, and dissolve in the oceans.
Through photosynthesis carbon dioxide enters plants and algae, bringing radiocarbon into the food chain. Radiocarbon then enters animals as they consume the plants figure 2. So even we humans are radioactive because of trace amounts of radiocarbon in our bodies. After radiocarbon forms, the nuclei of the carbon atoms are unstable, so over time they progressively decay back to nuclei of stable nitrogen This process is called beta decay.
The ejected electrons are called beta particles and make up what is called beta radiation. Not all radiocarbon atoms decay at the same time. Different carbon atoms revert to nitrogen at different times, which explains why radioactive decay is considered a random process. To measure the rate of decay, a suitable detector records the of beta particles ejected from a measured quantity of carbon over a period of time, say a month for illustration purposes.
Since each beta particle represents one decayed carbon atom, we know how many carbon atoms decayed during that month. Chemists have already determined how many atoms are in a given mass of each element, such as carbon. If we know what fraction of the carbon atoms are radioactive, we can also calculate how many radiocarbon atoms are in the lump. Knowing the of atoms that decayed in our sample over a month, we can calculate the radiocarbon decay rate. The standard way of expressing the decay rate is called the half-life. So if we started with 2 million atoms of carbon in our measured quantity of carbon, then the half-life of radiocarbon will be the time it takes for half, or 1 million, of these atoms to decay.
The radiocarbon half-life or decay rate has been determined at 5, years. Next comes the question of how scientists use this knowledge to date things. If carbon has formed at a constant rate for a very long time and continually mixed into the biosphere, then the level of carbon in the atmosphere should remain constant. If the level is constant, living plants and animals should also maintain a constant carbon level in them.
The reason is that, as long as the organism is alive, it replaces any carbon molecules that have decayed into nitrogen. After plants and animals perish, however, they no longer replace molecules damaged by radioactive decay. Instead, the radiocarbon atoms in their bodies slowly decay away, so the ratio of carbon atoms to regular carbon atoms will steadily decrease over time figure 3. Figure 3. After the death of an animal it no longer eats and adds 14 C to its body, so the 14 C in it is steadily lost by decay back to 14 N.
We can measure in the laboratory how many carbon atoms are still in the skull. If we assume that the mammoth originally had the same of carbon atoms in its bones as living animals do today estimated at one carbon atom for every trillion carbon atoms , then, because we also know the radiocarbon decay rate, we can calculate how long ago the mammoth died. This dating method is also similar to the principle behind an hourglass figure 4. The sand grains that originally filled the top bowl represent the carbon atoms in the living mammoth just before it died.
With time, those sand grains fell to the bottom bowl, so the new represents the carbon atoms left in the mammoth skull when we found it. The difference in the of sand grains represents the of carbon atoms that have decayed back to nitrogen since the mammoth died. Because we have measured the rate at which the sand grains fall the radiocarbon decay rate , we can then calculate how long it took those carbon atoms to decay, which is how long ago the mammoth died. Figure 4. A simple hourglass clock.
The sand grains in the top bowl fall to the bottom bowl to measure the passage of time. If all the sand grains are in the top bowl, then it takes exactly an hour for them all to fall. So if half the sand grains are in the top bowl and half in the bottom bowl, then 30 minutes has elapsed since the sand grains began falling.
We can calibrate an hourglass clock by timing the falling sand grains against a mechanical or electronic clock. But there is no way of independently calibrating the radioactive clocks in rocks because no observers were present when the rocks formed and the clocks started. So one would think that since the radiocarbon dating method works on organic once-living materials, then radiocarbon could be used to date fossils. After all, we should be able to estimate how long ago a creature lived based on how much radiocarbon is left in its body.
The answer is a matter of basic physics. Radiocarbon carbon is a very unstable element that quickly changes into nitrogen. Half the original quantity of carbon will decay back to the stable element nitrogen after only 5, years. This 5, year period is called the half-life of radiocarbon, figure 5. Figure 5. The decay of radiocarbon follows the exponential decay law, whereby the percentage decrease in the of parent atoms per unit time is constant.
After each half-life of 5, years, the of parent radiocarbon atoms remaining is halved. So if fossils are really millions of years old, as evolutionary scientists claim, no carbon atoms would be left in them. Indeed, if all the atoms making up the entire earth were radiocarbon, then after only 1 million years absolutely no carbon atoms should be left! Most laboratories measure radiocarbon with a very sophisticated instrument called an accelerator mass spectrometer, or AMS.
It is able to literally count carbon atoms one at a time. So rock samples that should read zero are occasionally placed into these instruments to test their accuracy. What better samples to use than fossils, coals, and limestones, which are supposed to be millions of years old and should have no radiocarbon? Figure 6. Distribution of 14 C values in samples of organic carbon from biologically derived materials such as fossils, limestones, coals, oils, natural gas, and graphite, as reported in the scientific literature.
All these samples are supposed to be millions of years old and should contain no detectable radiocarbon, according to the standard geological time scale. All these have been reported in the conventional scientific literature. This finding is consistent with the belief that rocks are only thousands of years old, but the specialists who obtained these have definitely not accepted this conclusion. It does not fit their presuppositions. To keep from concluding that the rocks are only thousands of years old, they claim that the radiocarbon must be due to contamination, either from the field or from the laboratory, or from both.
For some years creation scientists have been doing their own investigations of radiocarbon in fossils. Just as intriguing is the discovery of measurable radiocarbon in diamonds. Also, the tight bonding in their crystals would have prevented any carbon in the atmosphere from replacing any regular carbon atoms in the diamonds.
This is not a problem for creationist scientists, but it is a serious problem for evolutionists. Evolutionary radiocarbon scientists have still not conceded that fossils, coals, and diamonds are only thousands of years old. Among their proposed explanations is that the AMS instruments do not properly reset themselves between sample analyses. But if this were true, why does the instrument find zero atoms when no sample is in it?
The Flood cataclysm was only about 4, years ago. To solve this puzzle it is necessary to review the assumptions on which radiocarbon dating is based. These include None of these assumptions is strictly correct, beyond a rough first approximation. Indeed, scientists have now determined that the concentration of carbon in the atmosphere varies considerably according to latitude. They have also determined several geophysical causes for past and present fluctuations in carbon production in the atmosphere. Specifically, we know that carbon has varied in the past due to a stronger magnetic field on the earth and changing cycles in sunspot activity.
So when objects of known historical dates are dated using radiocarbon dating, we find that carbon dates are accurate back to only about B.Questions about carbon dating
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Carbon Dating Questions