Explain the difference between the law of superposition and radioactive dating

The law of superposition in sedimentary and extrusive igneous rocks states that an upper bed of rock is younger than a lower one, provided that earth-movements have not reversed the order. Radioactive dating is the use of radioactive elements to determine the age of different items. The premise of radioactive decay is dependent on the fact that unstable elements break down at a fixed rate into other elements. Hence the age of rocks containing radioactive elements can be determined.