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. 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 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, 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.Carbon-14 decays to nitrogen-14 by emitting an electron and a neutrino, and it does so with a half-life of 5,730 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.
Even with these weird––and challenging from an old-earth perspective––results, radiocarbon (or, carbon-14) dating remains one of the best tools for determining the ages of things that lived from 500 to 50,000 years ago. Carbon-14 (C) is a naturally occurring radioisotope of carbon and is found in trace amounts on Earth.It is produced in Earth’s atmosphere as cosmic rays hit nitrogen molecules and is then absorbed from the air by plants, which then pass it on to animals in the food chain.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.Would you trust a dating technique that said living mollusks had shells 2,300 years old, or worse, 27,000 years?
What if that same technique yielded dates for Triassic wood (when the dinosaurs lived) at 34,000 years and dated millions-of-years-old coal, oil, and even diamonds at less than 100,000 years? Libby and others in 1949, radiocarbon dating revolutionized archaeology––and other scientific fields––by establishing robust dates for organic materials of a biological origin like wood, bone, or shell.