When rocks are formed, small amounts of radioactive elements usually get included. As time passes, the "parent" radioactive element (which is uranium in this case) changes at a regular rate into non-radioactive "daughter" element (which is uranium in this case). Thus, the older a rock is, the larger the number of daughter atoms and the smaller the number of parent atoms are found in the rock. In this case as the rock ages, more and more of the uranium changes into lead.The of the rock in years can be found by measuring the rate at which a uranium decays and then measuring the ratio of uranium to lead in the rock.
Tuesday, November 30, 2010
Carbon-14 dating
Carbon-14 is a radioactive isotope of carbon with a nucleus containing 6 protons and 8 neutrons. Its presence in organic materials is the basis of the radiocarbon dating method to determine the age of fossils. Carbon has three naturally occurring isotopes. Both C-12 and C-13 are stable, but C-14 decays by very weak beta decay to nitrogen-14 with a half-life of approximately 5,730 years.
Cosmic ray protons blast nuclei in the upper atmosphere, producing neutrons which in turn bombard nitrogen of the atmosphere to produce the radioactive isotope carbon-14 according to the following reaction:
0n1 + 7N14→ 6C14 + 1H1
The radioactive carbon-14 combines with oxygen to form carbon dioxide.
Now plants take in CO2 for photosynthesis and so (while they are living) they have the same ratio of carbon 14 in them as the atmosphere. Animals, including humans, consume plants and thus they also tend to have the same ratio of carbon 14 to carbon 12 atoms. This equilibrium persists in living organisms as long as they continue living, but when they die the intake of carbon 14 stops.
Carbon 14 decays into nitrogen-14 through beta decay according to the following reaction:
6C14 → 7N14 + -1e0
Presuming the rate of production of carbon-14 to be constant, the ratio of C-14 and C-12 in a fossil can help us to determine the age of the fossil.
Cosmic ray protons blast nuclei in the upper atmosphere, producing neutrons which in turn bombard nitrogen of the atmosphere to produce the radioactive isotope carbon-14 according to the following reaction:
0n1 + 7N14→ 6C14 + 1H1
The radioactive carbon-14 combines with oxygen to form carbon dioxide.
Now plants take in CO2 for photosynthesis and so (while they are living) they have the same ratio of carbon 14 in them as the atmosphere. Animals, including humans, consume plants and thus they also tend to have the same ratio of carbon 14 to carbon 12 atoms. This equilibrium persists in living organisms as long as they continue living, but when they die the intake of carbon 14 stops.
Carbon 14 decays into nitrogen-14 through beta decay according to the following reaction:
6C14 → 7N14 + -1e0
Presuming the rate of production of carbon-14 to be constant, the ratio of C-14 and C-12 in a fossil can help us to determine the age of the fossil.
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