Radiometric dating half life definition
If one knows how much of this radioactive material was present initially in the object (by determining how much of the material has decayed), and one knows the half-life of the material, one can deduce the age of the object.
Scientists look at half-life decay rates of radioactive isotopes to estimate when a particular atom might decay.
Using the decays of uranium and thorium, our galaxy has been found to be between 10 and 20 billion years old and the earth has been found to be 4.6 billion years old. Within experimental error, this estimate agrees with the 15 billion year estimate of the age of the Universe.
The primary carbon-containing compound in the atmosphere is carbon dioxide, and a very small amount of carbon dioxide contains C-14.
Plants absorb C-14 during photosynthesis, so C-14 is incorporated into the cellular structure of plants.
But when the organism dies, the amount of C-14 begins to decrease.
Scientists know the half-life of C-14 (5,730 years), so they can figure out how long ago the organism died.The object's approximate age can then be figured out using the known rate of decay of the isotope.