Radio Carbon Dating?

Question

Well what i want to ask is what is radio carbon dating, i mean i know that it's something that helps sincentists use to determine how old the Earth is. and what is 14C and 12C and stuff like that.

thanks for your help

Answer 1

Radiocarbon dating is one of some dozens of techniques that are in use by geologists and others to determine how old things are.  Specifically, an incoming cosmic ray can change an atom of nitrogen to an atom of carbon 14, which can then be absorbed by a living thing or by being trapped in limestone.  The isotope is radioactive, and decays back to nitrogen with a half life of 5730 years, so by comparing the amount of carbon 14 present with that of carbon 12 (presumably entrained at the same time), one can get the age of the sample.   The rate of C-14 formation has changed somewhat over time, so the date from radioactive studies is compared with a standard obtained from dating tree rings, which of course give an exact date.  Because of this standardization, C-14 dating is the most accurate technology available, but it is limited to a few tens of thousands of years, after which the C-14 level becomes difficult to measure.

Many other radioactive elements are used for dating.  Of particular importance is uranium, because it is so ubiquitous; the two primordial uranium isotopes have half lives of 750 million and 4.5 billion years, so can easily be used to date rocks formed at any time after the earth formed.  Additional radioactive species used include thorium, potassium, and several others.

Date finding is not limited to the use of radioactive isotopes: any process that creates a separation between species over time can be used, and a dozen or more are now in use.  One of the more important ones has to do with disproportionation between the sulfur isotopes 32 and 34 (both stable); this has been used to date the formation of the oxygen-rich atmosphere to about 2.5 billion years ago.

Answer 2

Carbon dating is NOT used for determining how old the earth is!

This is a common misconception.

Carbon dating has a known range of only 60,000 years.  Therefore it is quite useless for dating rocks and fossils in the millions of years old ... let alone determining the age of the earth, which is currently quite confidently placed about about 4.5 billion years old.

So let me first answer your questions about carbon dating, and then describe how we get the age of the earth.

Carbon dating is useful for dating once-living animal or plant tissue (like wood, bone, skin, leather, paper, cloth, etc.), but not rocks or fossils.  

You asked about C12 and C14:   These are two types (called 'isotopes') of Carbon atom.   C12 is normal carbon and has 6 protons and 6 neutrons in the nucleus (for a total of 12).  C14 has 6 protons and 8 neutrons (for a total of 14).  C14 is created in the upper atmosphere when a Nitrogen atom (7 protons, 7 neutrons) is hit by a cosmic ray, and one of those protons is replaced by a neutron.   However, that C14 atom is unstable, and eventually will decay back into Nitrogen-14.  It takes about 5,730 years for half of the C14 to decay back into Nitrogen.

Both kinds of C atom bond with oxygen to make CO2 molecules ... it doesn't matter to the molecule whether that C atom is a C12 or C14 ... it has exactly the same chemical properties.   We know from measurement that for every 1 trillion CO2 molecule with a C12 in it, there is a single C02 molecule with a C14 in it.   This hasn't changed much in the last 60,000 years (which is a fairly short amount of time in geologic terms), except for the last 200 years when humans have been putting a lot of burned CO2 back into the atmosphere.

When plants breathe in CO2, the breath out O2, and use that carbon atom in it their bodies.  So the ratio of C12 to C14 atoms in the body of a living plant is the same as it is in the atmosphere (1 trillion to one).  The same applies to any animal that eats that plant.

But when that animal or plant dies, it stops taking on new Carbon atoms, and the C14 atoms start decaying into Nitrogen.  When they decay, they are released as gaseous Nitrogen, so it is like the C14 atom just disappeared.

So by measuring the ratio of C12 to C14 atoms in any dead tissue (e.g. wood or paper left by a tree, or ancient bones left by a dead wooly mammoth), and knowing the rate of C14 decay, we can compute the age of the object.

BUT because it decays at a rate of half-gone every 5730 years, by the time something is 60,000 years old there is so little C14 left that our instruments can't measure it.

So for much older objects (rocks, fossils, meteorites into the millions of years) we use many other methods based on different radioactive isotopes.  (E.g. potassium decays into argon gas, or uranium decays into lead.)  

The principle is the same ... the constant decay of radioactive isotopes.  But in this case they have a *much* slower decay rate (rather than 5,730 years, they can last millions, or in some cases *billions* of years).  Also, these are not dependent on knowing the ratio in the atmosphere, but in rocks as they form in volcanoes.

For example, Potassium-40 decays into Argon-40.  Potassium gets solidified into rocks when they form, but Argon doesn't (it escapes as a gas).  However once the rock is solid, any Argon atoms produced by Potassium decay are trapped in the rock.

So millions of years later, if we measure the ratio of Potassium-40 to Argon-40, and knowing the rate of decay ... we can again compute the age of the rock.

Finally, we don't just use one method.   There are *dozens* of different isotopes, that all decay at different rates from each other ... and they all come up with the same numbers.

The oldest rocks we have measured are 4.4 billion years old.   The oldest meteorites (which were formed at the birth of the solar system ... a little older than the earth) are 4.6 billion years old.  So that means that the age of the earth is between 4.4 and 4.6 billion years old.

Hope that answers your question.

Answer 3

c-14 and c-12 are differnt ions of carbon (c)... the amount of carbon in a substance can tell us how old the thing is because of carbons half life.... after so many years only half of the orginal amount of carbon is left and that's what is measured in carbon dating

Answer 4

Radio carbon dating uses the amount of Carbon 14 (14C) to tell how how old something is, since Carbon 14 decomposes into carbon 12 (12C) at a known rate, so finding the ratio is finding the age as well.

Answer 5

Carbon 14 dating or Radio Carbon dating is figuring out the age of a substance from the amount of Carbon-14 remaining in it. Carbon-14 is a radioactive isotope of Carbon with a half-life of 5730 years. 14C and 12C are just isotopes of Carbon. The number indicates the mass of the isotope.