I need an accurate, but simple expaination as to how carbon dateing works?

Question

need to be able to explain to class of kids how the process works and why it is considered so reliable.

Answer 1

Although some of the answers you have received are accurate they aren’t exactly succinct or to the point.
You haven’t however said what age the kids are you need to explain it to, please forgive me if this explanation seems too simplistic.
The theory of radioactive dating works along these lines.

1. SOME ELEMENTS “DECAY” (CHANGE) FROM ONE THING TO ANOTHER, e.g. from Potassium to Argon or from one isotope to another e.g. C14 to C12
2. THIS RATE OF CHANGE IS KNOWN, the speed at which it changes is known as the half life, i.e. how long before half of the total has changed
3. A COMPARISON IS MADE i.e. you work out how much there was and how much has changed
4. THE AGE IS CALCULATED. Once you know how much has decayed you can compare the amounts on well-known charts e.g. if you know halve the amount of C14 has changed to C12 then the sample is 5730 years old.

It is considered accurate because the rate of radioactive decay is absolute, measurable and observable. It has been tested numerous times and can be experimented on. The same results can be achieved and repeated by numerous people at many different labs. On the whole the decayed products (e.g. C12 etc.) are not found naturally. The original material is created at the time the sample is formed or moved (e.g. when the plant, animal grew).

However the problems are
1. In order to calculate the percentage of element changed you have to know how much there was. Sometimes the sample can have some of the original material removed or more of the original material can be added, e.g. new living fungi can grow and die on a log hundreds of years after the log was originally felled and buried.( this would give a younger date)
2. The resulting product can be removed or further altered e.g. Argon from potassium can escape as it is a gas ( this would give you a later date because it would seem not as much or the argon had been formed)
3. This time clock can be reset due to outside influences. A fire can reset the amount of C14/C12 because the carbon from the fire is different from the carbon formed in the living thing (e.g. the problems with dating the shroud of Turin)

This of coarse assumes that the equipment used is accurate and that no contamination was added e.g. someone touching or sneezing on the sample.

On the whole though in theory the method should be extremely accurate. Given perfect samples, good laboratory practice and accurate measurements the results seem impressive. This shouldn’t automatically however be taken for granted.

The final thing to remember though is that there is no other way of giving empirical, measurable dates on extremely ancient rocks or artefacts.

Answer 2

You eat foods. A large component of food is carbon. (By definition, the presence of carbon in anything more complicated than CO or CO2 is the definition of organic matter.)

Carbon is a natural mix of carbon-12, the stable kind, and carbon-14, a radioactive isotope. Based on percentages in the air, a certain percentage of the carbon in your body should be carbon-14. Carbon-14 is always decaying at a measurable rate, but you are always breathing in new carbon-14 to replace the decayed stuff. While you live, the percentage of carbon-12 to carbon-14 in you should match the rest of the atmosphere.

When you die, you stop breathing, so the carbon-14 in your body stops being replaced. Any that decays decreases the ratio of carbon-14 to carbon-12.

When we come back years later and measure that ratio, we can compare the change to the expected value and calculate how many half-lives of carbon-14 ago you died.

Because so many things come from or contain organic material: clothes, paper, clay, etc; carbon-14 dating is a good way to measure relatively recent ages.

Answer 3

All living organisms incorporate the (radioactively unstable)carbon-14 isotope (originally harvested from the atmosphere by photosynthetic organisms) into their bodies, along with radioactively stable isotope carbon-12. Upon death, no more C14 is added and this isotope begins to decay, with a half-life of about 6000 years. By measuring the proportion of stable C12 to unstable C14, an estimation of age since death can be calculated by comparing the ratio of C12 to C14 - the less C14 (more decay) the older the sample is. This is good for dating samples up to about 50,000 years as complete decay of C14 results in it's reversion to Nitrogen-14.

Answer 4

Let me first explain how carbon dating works and then show you the assumptions it is based on. Radiation from the sun strikes the atmosphere of the earth all day long. This energy converts about 21 pounds of nitrogen into radioactive carbon 14. This radioactive carbon 14 slowly decays back into normal, stable nitrogen. Extensive laboratory testing has shown that about half of the C-14 molecules will decay in 5730 years. This is called the half-life. After another 5730 years half of the remaining C-14 will decay leaving only ¼ of the original C-14. It goes from ½ to ¼ to 1/8, etc. In theory it would never totally disappear, but after about 5 half lives the difference is not measurable with any degree of accuracy. This is why most people say carbon dating is only good for objects less than 40,000 years old. Nothing on earth carbon dates in the millions of years, because the scope of carbon dating only extends a few thousand years. Willard Libby invented the carbon dating technique in the early 1950's. The amount of carbon 14 in the atmosphere today (about .0000765%), is assumed there would be the same amount found in living plants or animals since the plants breath CO2 and animals eat plants. Carbon 14 is the radio-active version of carbon.

Since sunlight causes the formation of C-14 in the atmosphere, and normal radioactive decay takes it out, there must be a point where the formation rate and the decay rate equalizes. This is called the point of equilibrium. Let me illustrate: If you were trying to fill a barrel with water but there were holes drilled up the side of the barrel, as you filled the barrel it would begin leaking out the holes. At some point you would be putting it in and it would be leaking out at the same rate. You will not be able to fill the barrel past this point of equilibrium. In the same way the C-14 is being formed and decaying simultaneously. A freshly created earth would require about 30,000 years for the amount of C-14 in the atmosphere to reach this point of equilibrium because it would leak out as it is being filled. Tests indicate that the earth has still not reached equilibrium. There is more C-14 in the atmosphere now than there was 40 years ago. This would prove the earth is not yet 30,000 years old! This also means that plants and animals that lived in the past had less C-14 in them than do plants and animals today. Just this one fact totally upsets data obtained by C-14 dating.

The carbon in the atmosphere normally combines with oxygen to make carbon dioxide (CO2). Plants breathe CO2 and make it part of their tissue. Animals eat the plants and make it part of their tissues. A very small percentage of the carbon plants take in is radioactive C-14. When a plant or animal dies it stops taking in air and food so it should not be able to get any new C-14. The C-14 in the plant or animal will begin to decay back to normal nitrogen. The older an object is, the less carbon-14 it contains. One gram of carbon from living plant material causes a Geiger counter to click 16 times per minute as the C-14 decays. A sample that causes 8 clicks per minute would be 5,730 years old (the sample has gone through one half life), and so on. (See chart on page 46 about C-14). Although this technique looks good at first, carbon-14 dating rests on two simple assumptions. They are, obviously, assuming the amount of carbon-14 in the atmosphere has always been constant, and its rate of decay has always been constant. Neither of these assumptions is provable or reasonable.

An illustration may help: Imagine you found a candle burning in a room, and you wanted to determine how long it was burning before you found it. You could measure the present height of the candle (say, seven inches) and the rate of burn (say, an inch per hour). In order to find the length of time since the candle was lit we would be forced to make some assumptions. We would, obviously, have to assume that the candle has always burned at the same rate, and assumes an initial height of the candle.
The answer changes based on the assumptions. Similarly, scientists do not know that the carbon-14 decay rate has been constant. They do not know that the amount of carbon-14 in the atmosphere is constant. Present testing shows the amount of C-14 in the atmosphere has been increasing since it was first measured in the 1950's. This may be tied in to the declining strength of the magnetic field.

Answer 5

Carbon 14 is a radioactive isotope of carbon. It is produced in the upper atmosphere by radiation from the sun. (Specifically, neutrons hit nitrogen-14 atoms and transmute them to carbon.)
Land plants, such as trees, get their carbon from carbon dioxide in the air. So, some fraction of their carbon is C14. The same is true of any creature that gets its carbon by eating such plants. We can measure this in living things today.

Suppose such a creature dies, and the body is preserved. The C14 will undergo radioactive decay, and after 5730 years, half of it will be gone. Eventually, all of it will be gone. So, if we find such a body, the amount of C14 in it will tell us how long ago it was alive.

Answer 6

Because Carbon 14 is radioactive and decays, the ratio of Carbon 14 and Carbon 16 changes as time progresses after an animal dies.
The measurement of this ratio enables the calculation of the very aproximate time of death.
Hope this helps

Answer 7

The isotope of varbon C14 has a half life of 5730 years that means that after 5730 years the amount of C14 present in an object will become half it's size . Therefore by measuring the quantity of C14 present in a substance we can know how old the object is.

Answer 8

Okay, I'll try:

Carbon breaks down over time.
We know how long it takes for it to break down.
By measuring the residu of carbon left in the object (providing we know how much carbon was in it in the first place, but we do know that) we can therefore calculate how old the object must be.

this is as simple as I can make it :-)

Answer 9

Radiometric dating in general is not reliable at all.
It is based on too many unverifiable assumptions, as other posters have mentioned.


Teach you kids to question peoples' assumptions, and their philosophical motiviations.

Coal is claimed to be millions of years old yet generally has measurable amounts of C14, indicating youth.

Answer 10

all living things contain carbon. when they die, the amount of carbon in their bodies reduces gradually. they measure the amount of carbon in a dead thing and figure out how old it is....I think.