BBC - GCSE Bitesize: Carbon dating
While the lighter isotopes 12C and 13C are stable, the heaviest isotope 14C ( radiocarbon) is radioactive. This means its nucleus is so large that. The most common of the radioactive dating techniques currently in use involves the isotope 14 of carbon, the radiocarbon. This radioactive isotope of carbon is. Carbon is a weakly radioactive isotope of Carbon; also known as radiocarbon , it is an isotopic chronometer. C dating is only applicable to organic and.
The first method for dating organic objects such as the remains of plants and animals was developed by another American chemist, Willard Libby — He became intrigued by carbon—14, a radioactive isotope of carbon. Carbon has isotopes with atomic weights between 9 and The most abundant isotope in nature is carbon—12, followed in abundance by carbon— Among the less abundant isotopes is carbon—14, which is produced in small quantities in the earth 's atmosphere through interactions involving cosmic rays.
In any living organism, the relative concentration of carbon—14 is the same as it is in the atmosphere because of the interchange of this isotope between the organism and the air. This carbon—14 cycles through an organism while it is alive, but once it dies, the organism accumulates no additional carbon— Whatever carbon—14 was present at the time of the organism's death begins to decay to nitrogen—14 by emitting radiation in a process known as beta decay.
The difference between the concentration of carbon—14 in the material to be dated and the concentration in the atmosphere provides a basis for estimating the age of a specimen, given that the rate of decay of carbon—14 is well known.
The length of time required for one-half of the unstable carbon—14 nuclei to decay i. Libby began testing his carbon—14 dating procedure by dating objects whose ages were already known, such as samples from Egyptian tombs. He found that his methods, while not as accurate as he had hoped, were fairly reliable. Libby's method, called radiocarbon or carbon—14 dating, gave new impetus to the science of radioactive dating.
Using the carbon—14 method, scientists determined the ages of artifacts from many ancient civilizations. Still, even with the help of laboratories worldwide, radiocarbon dating was only accurate up to 70, years old, since objects older than this contained far too little carbon—14 for the equipment to detect.
As a result, animal and plant life regularly assimilate carbon 14 atom together with the usual carbon The carbon 14 present in the atmosphere is constantly renewed. The cosmic rays originating from the Sun collide with nuclei in the upper atmosphere and are capable of breaking off individual neutrons.
These neutrons, once freed, can interact with atoms of nitrogen 14 in air, causing the expulsion of a proton and the formation of carbon IN2P3 One naturally assumes that the cosmic bombardment responsible for this transmutation remains constant over the millennia.
The rate of cosmic rays which hit the Earth depends on two very slowly changing factors: This latter serves as a shield against all cosmic radiation - when its strength goes down, the bombardment increases, as does the number of carbon 14 atoms. All living beings assimilate carbon dioxide molecules, a fixed but very small fraction of which contains carbon This assimilation stops upon the death of the organism, thus halting the absorption of any more carbon The atoms of carbon 14 then proceed to decay exponentially, with a half life of 5, years.
When much later, an archaeologist examines the remains fireplace ashes, bones, plant remainshe can date the fossil by comparing the fraction of remaining radiocarbon nuclei to the fraction existing at the time the organism stopped absorbing carbon.
The fundamental hypothesis in these estimations is that the rate of radioactive carbon existing when the organism was living would have been the same as the rate in a similar organism alive today.
What is Carbon (14C) Dating? Carbon Dating Definition
The ratio of the activities of the fossilized and living bodies then provides an age. The estimation assumes that the rate of formation of atmospheric carbon 14 has not changed since the days when the fossil was alive.
This is not entirely true and it is necessary to readjust the time and make corrections.