It's this resetting process that gives us the ability to date rocks that formed at different times in earth history.
A commonly used radiometric dating technique relies on the breakdown of potassium (Ar in an igneous rock can tell us the amount of time that has passed since the rock crystallized.
Radiometric dating is possible because the radioactive decay of large numbers of radioactive atoms follows a predictable pattern.This predictability allows scientists to measure the age of an object if they can work out how many radioactive atoms were originally present.If an igneous or other rock is metamorphosed, its radiometric clock is reset, and potassium-argon measurements can be used to tell the number of years that has passed since metamorphism.Carbon-14 is a method used for young (less than 50,000 year old) sedimentary rocks.The original radioactive atom is known as a parent isotope, while the atom produced by the decay process is known as a daughter isotope. For example Uranium-235 and Uranium-238 are both Uranium atoms with the same number of protons, but they have a different number of neutrons.
The number used to identify the isotope refers to the total number of particles in the nucleus of each atom.This is used to date the remains of things that were once living.All living things absorb Carbon from the atmosphere into their bodies, and excrete Carbon back into the environment.Radioactive decay allows geologists and physicists to measure the age of ancient fossils, rocks and even the Earth.This process is called radiometric or radioactive dating.Relative dating methods can not establish exactly how old things are, but only how old things are relative to other things.