3 radioactive elements in absolute dating
The rates of decay of various radioactive isotopes have been accurately measured in the laboratory and have been shown to be constant, even in extreme temperatures and pressures.These rates are usually expressed as the isotope's half-life--that is, the time it takes for one-half of the parent isotopes to decay.
Radiometric dating has shown that very old rocks--3.5 billion years or older--occur on all the continents.We know the Earth must be at least as old as any rock on it.Unfortunately, none of the original rocks still exist, so scientists had to use less direct evidence to determine the age of the Earth.The discovery gave scientists a tool for dating rocks that contain radioactive elements.
Many elements have naturally occurring isotopes, varieties of the element that have different numbers of neutrons in the nucleus.
Over time, radioactive isotopes change into stable isotopes by a process known as radioactive decay.