Radiometric dates calculated from minerals in sedimentary rocks produce ages that are too old and often predates the sedimentary deposition.
Radiometric dating involves the uses of radioactive elements in rocks to measure the absolute age of rock.
It involves comparing the daughter to parent ratio because the decay started when the minerals formed in a rock in a period of crystallization or metamorphic event.
Sedimentary rocks are often made up of re-worked minerals.
They are derived from pre-existing igneous and metamorphic rocks.
When radioactive minerals from these sources finds their way into sediments, they give the age of their parent rock and not that of the sedimentary rock because their activity is not being reset.
