Emitting these particles transforms the unstable atoms into different, more stable elements.
The rate of decay is described by the half-life of the isotope—the average time an atom of a radioactive element remains in the parent state.When the half-life has elapsed, half the parent element will have decayed into the daughter element.Potassium-40, for example, decays into Argon-40 with a half-life of 1.25 billion years, so that after 1.25 billion years half of the Potassium-40 in a rock will have become Argon-40.This means that if a rock sample contained equal amounts of Potassium-40 and Argon-40, it would be 1.25 billion years old.Atoms are composed of a nucleus orbited by negatively charged electrons.The nucleus is made up of protons, particles with a positive charge, and neutrons, particles with no charge.
Every atom of a given element has the same number of protons in the nucleus. Different isotopes of a given element have the same number of protons but a different number of neutrons.
Radioactive elements are unstable atoms that give off particles.
Radiometric Dating Radiometric dating provides science with a powerful tool for reconstructing our planet’s history. Boltwood, a radiochemist at Yale University, made the first attempt to establish a geologic time scale.
The idea that radioactivity could be used as a measure of the age of geologic formations was first suggested in 1905 by a British physicist, Lord Rutherford. The invention of the mass spectrometer after World War I led to the discovery of isotopes (see below) and the calculation of accurate decay rates.
Not until the 1950s, however, was precise dating achieved and accepted by the scientific community.
The methodologies and instruments for radiometric dating have been expanded and fine-tuned in the half-century since, and very accurate dating is now possible.