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Carbon-14 dating is a way of determining the age of certain archeological artifacts of a biological origin up to about 50,000 years old. It is used in dating things such as bone, cloth, wood and plant fibers that were created in the relatively recent past by human activities.
Cosmic rays enter the earth's atmosphere in large numbers every day. For example, every person is hit by about half a million cosmic rays every hour. It is not uncommon for a cosmic ray to collide with an atom in the atmosphere, creating a secondary cosmic ray in the form of an energetic neutron, and for these energetic neutrons to collide with nitrogen atoms. When the neutron collides, a nitrogen-14 (seven protons, seven neutrons) atom turns into a carbon-14 atom (six protons, eight neutrons) and a hydrogen atom (one proton, zero neutrons). Carbon-14 is radioactive, with a half-life of about 5,700 years.
As soon as a living organism dies, it stops taking in new carbon. The ratio of carbon-12 to carbon-14 at the moment of death is the same as every other living thing, but the carbon-14 decays and is not replaced. The carbon-14 decays with its half-life of 5,700 years, while the amount of carbon-12 remains constant in the sample. By looking at the ratio of carbon-12 to carbon-14 in the sample and comparing it to the ratio in a living organism, it is possible to determine the age of a formerly living thing fairly precisely.
A formula to calculate how old a sample is by carbon-14 dating is:


t = [ ln (Nf/No) / (-0.693) ] x t1/2
where ln is the natural logarithm, Nf/No is the percent of carbon-14 in the sample compared to the amount in living tissue, and t1/2 is the half-life of carbon-14 (5,700 years).

So, if you had a fossil that had 10 percent carbon-14 compared to a living sample, then that fossil would be:


t = [ ln (0.10) / (-0.693) ] x 5,700 years
t = [ (-2.303) / (-0.693) ] x 5,700 years

t = [ 3.323 ] x 5,700 years

t = 18,940 years old

Because the half-life of carbon-14 is 5,700 years, it is only reliable for dating objects up to about 60,000 years old. However, the principle of carbon-14 dating applies to other isotopes as well. Potassium-40 is another radioactive element naturally found in your body and has a half-life of 1.3 billion years. Other useful radioisotopes for radioactive dating include Uranium -235 (half-life = 704 million years), Uranium -238 (half-life = 4.5 billion years), Thorium-232 (half-life = 14 billion years) and Rubidium-87 (half-life = 49 billion years).

The use of various radioisotopes allows the dating of biological and geological samples with a high degree of accuracy. However, radioisotope dating may not work so well in the future. Anything that dies after the 1940s, when Nuclear bombs, nuclear reactors and open-air nuclear tests started changing things, will be harder to date precisely.

2007-10-13 11:56:49 · answer #1 · answered by Songbyrd JPA ✡ 7 · 2 1

Carbon Dating

2007-10-13 11:51:06 · answer #2 · answered by Veritas 7 · 1 0

"Is it true that Bronze Age goat herders have nothing to teach us?" I don't think that your examples are particularly convincing, as other mythologies have similar elements and there is a big difference between stating something as a matter of belief ("the world will end in fire") and having some understanding of why that might, potentially happen. Equating a belief in angels and demons with a belief in aliens is particularly dubious. Unfortunately the only lesson which a number of people have picked up from the Bronze Age Goat Herders is the one about how they've been given the Promised Land by God and that if anyone gets in their way while taking it over it's fine to slaughter them down to the last infant.

2016-05-22 06:49:43 · answer #3 · answered by amada 3 · 0 0

To get absolute dates - that is, dates that can be tied to our own calendar, the following methods would be used:
If the remains are around 40,000 years old or younger then carbon dating/radiocarbon/C14 dating is typically used. Carbon dating is not particularly useful for organic remains older than 40,000 years.
For older specimens, Potassium-Argon dating is generally preferred, as it is reasonably accurate to about 1.3 million years ago. Unfortunately, P-A dating does not work on organic remains. It must be used on stone. In the case of fossilized remains, it may be possible to test the fossil itself (though this is generally not preferred as it can be destructive). Instead, (typically) rock samples from immediately around the remains are tested. There are disadvantages with Potassium-Argon dating, as it only dates when the object was last heated to a particular temperature. While useful for things like ceramics or to date metamorphic rock formations, it can be a bit challenging with other types of remains.

2007-10-13 14:12:42 · answer #4 · answered by F 5 · 0 1

They use multiple methods. They look at the soil and rock layers, they use carbon dating based on the rate of carbon release from organics, they also look for remains of other past organisms of time periods. I know there are some more methods, but they are not coming to mind right now. Maybe some of the other answerer's will know.

2007-10-13 11:54:23 · answer #5 · answered by suigeneris-impetus 6 · 2 1

Carbon dating, and also how deep they were found, and where, than compare it to bones found in a simular way and brain storm.

2007-10-13 12:20:01 · answer #6 · answered by Beth 2 · 0 1

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