Radiometric dating is used to tell the absolute age of materials by studying the decay rate of radioactive isotopes. the decay rates of isotopes are constant and are expressed as daughter isotopesparent isotopesquarter-liveshalf-lives .

The decay rates of isotopes are constant and are expressed as half-lives. Half-life is the known time for a radioactive material to decrease its radioactivity by one half of its initial value. Different materials have corresponding half-life constants which are then used as the basis for computing their age. Half-life can be calculated using the formula:

t(1/2) = ln(2)/k

where:
t(1/2) = half life
k = rate constant

Ba population changes in response to a change in environment

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