Dating a Fossil 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.
Radioactive dating is used in the determination of carbon-14 constituent in the ancient specimen or fossil. This radiocarbon or carbon-14 refers to a naturally happening component that is produced when the cosmic rays in the atmosphere come in contact with the nitrogen atoms that then oxidizes to produce carbon dioxide.
This carbon dioxide is consumed by the plants and is also conducted towards the animals feeding on them. After an organism's death, the concentration of carbon-14 diminishes with the decay of the organism. It exhibits a half-life of 5700 years that signifies that the carbon-14 diminishes to half in concentration after 5700 years. The fossils from the previous 70000 years that were formed of charcoal, wood, bone can be dated with the help of this technique.
Charles Darwin; he studied the different beak shapes/sizes of Galapagos finches and found that over time, they changed due to their needs for the food found around them (evolution).
