Radiocarbon dating is a method for determining the age of an object containing organic .. This means that after 5, years, only half of the initial a chemical analysis used to determine the age of organic materials based on their content of the radioisotope carbon; believed to be reliable up to Carbon dating definition: Carbon dating is a system of calculating the age of a very old by measuring the amount of radioactive carbon remaining in them.
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This is a first order reaction equation and the rate at which it the reaction proceeds over time can be modeled by the equations: A reaction with a large rate constant has a short half-life. Libby Was the man who first developed the idea and procedure for Carbon dating. He measured the half-life of Carbon to be about 5, years. However after about 50, years there is so little Carbon left in the specimen that it is very hard, almost impossible, to calculate its age.
Van Der Merwe Libby ran many tests on items where the age was known, or estimated by other means. His test results came rather close, to within plus or minus a few hundred years. Poole In the laboratory, samples must be processed and cleaned so that there is no material on them that might throw off the age reading. Then the sample is burned and passes through a completely sterile vacuum system as Carbon dioxide gas.
The gas is then subjected to more purifying procedures. Afterward the gas is stored in a tube insulated by Mercury and Lead, so as to minimize the chances of the sample being affected by radiations from the atmosphere. When a Carbon atom disintegrates fine instruments detect the action, a light flashes on a control panel, and a counter records the number of decaying atoms. By this method the scientist can keep track of how many atoms are decomposing per minute and per second.
Poole This sounds great! We are now ably to date anything we want, even that something at the back of the fridge, and know how old it is within a few hundred years, but are there any problems with the Carbon dating method? In order to know how long a sample of radioactive material had been decomposing we need three variables defined, how much of the sample we have left now, what the half-life of the sample is, and how much of the sample we started out with.
For Carbon dating we have already experimentally measured the amount of Carbon left, and Libby has already measured the half-life of Carbon to an acceptable exactness, however how much Carbon was there in the specimen at the time of death.
The amount of Carbon in an organic body is constant with the amount of Carbon in the atmosphere. Thus specimens have the same amount of carbon in them as the rest of the atmosphere at the time that the specimen lived.
However, if we could measure the amount of Carbon in the atmosphere when they lived, we would be living during the time and there would be no reason for dating. A recent proof of that would be the Industrial revolution. Factories put out massive amounts of Carbon, and during that time the concentration of Carbon in the atmosphere increased significantly. Fortunately, Libby was a smart guy and accounted for this discrepancy. He measured the amount of Carbon in the inner layers of trees that were older than the Industrial revolution.
He was able to calculate the amount of Carbon in the atmosphere, before the industrial revolution, and adjust his equation accordingly. Can this be assumed to be correct? In the atmosphere the amount of Carbon decaying over time increases with the greater concentration of Carbon in the atmosphere. Eventually the reaction would reach some equilibrium and the amount of Carbon in the atmosphere would remain constant.
Scientists have calculated that the amount Carbon in the atmosphere would become stable after 30, years from the beginning of the reaction.
The reaction must have started when the Earth was formed, and thus the reaction would reach equilibrium after the Earth was 30, years old. Scientists have assumed that the Earth is many millions of years old, however, no one was living when the earth was formed, and no one has concrete proof as to when the Earth was formed and therefore no one can say exactly how old it is. This would seem to indicate a reaction that is not yet in equilibrium. These results were within his error margins and thus were ignored.
For instance, bones of a sabre-toothed tiger, theorized to be between , and one million years old, gave a Carbon date of 28, years. A freshly killed seal, dated using Carbon, showed it had died years ago. Living mollusk shells were dated at up to 2, years old. An isotope, the protons define what element it is. But this number up here can change depending on the number of neutrons you have. So the different versions of a given element, those are each called isotopes.
I just view in my head as versions of an element. So anyway, we have our atmosphere, and then coming from our sun, we have what's commonly called cosmic rays, but they're actually not rays.
You can view them as just single protons, which is the same thing as a hydrogen nucleus. They can also be alpha particles, which is the same thing as a helium nucleus. And there's even a few electrons. And they're going to come in, and they're going to bump into things in our atmosphere, and they're actually going to form neutrons. So they're actually going to form neutrons. And we'll show a neutron with a lowercase n, and a 1 for its mass number. And we don't write anything, because it has no protons down here.
Like we had for nitrogen, we had seven protons. So it's not really an element. It is a subatomic particle. But you have these neutrons form. And every now and then-- and let's just be clear-- this isn't like a typical reaction.
But every now and then one of those neutrons will bump into one of the nitrogen's in just the right way so that it bumps off one of the protons in the nitrogen and essentially replaces that proton with itself.
So let me make it clear. So it bumps off one of the protons. So instead of seven protons we now have six protons. But this number 14 doesn't go down to 13 because it replaces it with itself. So this still stays at And now since it only has six protons, this is no longer nitrogen, by definition.
This is now carbon. And that proton that was bumped off just kind of gets emitted. So then let me just do that in another color. And a proton that's just flying around, you could call that hydrogen 1. And it can gain an electron some ways. If it doesn't gain an electron, it's just a hydrogen ion, a positive ion, either way, or a hydrogen nucleus. But this process-- and once again, it's not a typical process, but it happens every now and then-- this is how carbon forms.
So this right here is carbon You can essentially view it as a nitrogen where one of the protons is replaced with a neutron. And what's interesting about this is this is constantly being formed in our atmosphere, not in huge quantities, but in reasonable quantities. So let me write this down. And let me be very clear. Let's look at the periodic table over here.
So carbon by definition has six protons, but the typical isotope, the most common isotope of carbon is carbon So carbon is the most common. So most of the carbon in your body is carbon But what's interesting is that a small fraction of carbon forms, and then this carbon can then also combine with oxygen to form carbon dioxide. And then that carbon dioxide gets absorbed into the rest of the atmosphere, into our oceans. It can be fixed by plants.
When people talk about carbon fixation, they're really talking about using mainly light energy from the sun to take gaseous carbon and turn it into actual kind of organic tissue. And so this carbon, it's constantly being formed. It makes its way into oceans-- it's already in the air, but it completely mixes through the whole atmosphere-- and the air.
And then it makes its way into plants. And plants are really just made out of that fixed carbon, that carbon that was taken in gaseous form and put into, I guess you could say, into kind of a solid form, put it into a living form.
That's what wood pretty much is. It gets put into plants, and then it gets put into the things that eat the plants.
So that could be us. Now why is this even interesting?
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