Since the half-life of carbon-14 is 5730 years, scientists can measure the age of a sample by determining how many times its original carbon-14 amount has been cut in half since the death of the organism.
For example, an object with a quarter of its original amount (2x1/2) should be roughly 11,460 years old.
Before then, the Bible had provided the only estimate for the age of the world: about 6,000 years, with Genesis as the history book.
The age of the planet, though, was important to Charles Darwin and other evolutionary theorists: The biological evidence they were collecting showed that nature needed vastly more time than previously thought to sculpt the world.A breakthrough came with the discovery of radioactivity at the beginning of the 1900s.Certain isotopes are unstable and undergo a process of radioactive decay, slowly and steadily transforming, molecule by molecule, into a different isotope.This rate of decay is constant for a given isotope, and the time it takes for one-half of a particular isotope to decay is its radioactive half-life.This means that lifeless organic matter is effectively a closed system, since no carbon-14 enters the organism after death, an occurrence that would affect accurate measurements.
In radiometric dating, the decaying matter is called the parent isotope and the stable outcome of the decay is called the daughter product.Geologist Ralph Harvey and historian Mott Greene explain the principles of radiometric dating and its application in determining the age of Earth.As the uranium in rocks decays, it emits subatomic particles and turns into lead at a constant rate.Using this technique, called radiometric dating, scientists are able to "see" back in time.As shown in the diagram above, the radioactive isotope carbon-14 originates in the Earth's atmosphere, is distributed among the living organisms on the surface, and ceases to replenish itself within an organism after that organism is dead.Uranium-lead dating is one of the most complicated of all dating techniques.