Carbon 14 dating 1 (video) | Khan Academy
Carbon dating is a variety of radioactive dating which is applicable only to matter Carbon decays with a halflife of about years by the emission of an Radioactive carbon is being created by this process at the rate of about two. Carbon dating, also called radiocarbon dating, method of age determination that Carbon has a half-life of 5, ± 40 years—i.e., half the amount of the. Scientists use Carbon dating for telling the age of an old object, whose origin and Willard F. 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, plants and animals that are still alive constantly replace the supply of carbon in their systems and so the amount of Carbon in the system stays almost constant. Once a plant or animal dies the Carbon is no longer being regenerated and so the Carbon starts to decay. In this way, by measuring the amount of Carbon in the body of a prehistoric animal or plant, a scientist can deduce when the plant or animal died.
All radioactive materials have a half-life. If you have a certain amount of a radioactive material, its half-life is the time it takes for half of the material you started out with to decay.
Carbon decays back into nitrogen. 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.
How Carbon Dating Works | HowStuffWorks
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.
Carbon dating | scientific technology | n3ws.info
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.
How Carbon-14 Dating Works
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. And then either later in this video or in future videos we'll talk about how it's actually used to date things, how we use it actually figure out that that bone is 12, years old, or that person died 18, years ago, whatever it might be.
So let me draw the Earth. So let me just draw the surface of the Earth like that. It's just a little section of the surface of the Earth. And then we have the atmosphere of the Earth. I'll draw that in yellow. So then you have the Earth's atmosphere right over here. Let me write that down, atmosphere. And I'll write nitrogen. Its symbol is just N. And it has seven protons, and it also has seven neutrons.
So it has an atomic mass of roughly Then this is the most typical isotope of nitrogen.
And we talk about the word isotope in the chemistry playlist. 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