What is a disadvantage of radiometric dating using potassium 40
If the concentration of argon-40 is almost zero, then the rock was formed recently.If it is high relative to the amount of potassium-40 present, then the rock is old.Potassium-argon dating is a method for estimating the age of volcanic rocks by measuring the ratio of potassium-40 to argon-40 present.The method is based on the fact that the potassium-40 isotope of potassium decays over time to form argon-40.
If the rate of radioactive decay has changed over time, the formula will not give correct dates.Most scientists believe that the rate of potassium-argon decay has not changed over the history of the earth.The useful fact about these two substances is that at normal temperatures, potassium is a solid, but argon is a gas.Therefore, during volcanic eruptions, any argon that is present escapes from the rock.
But after the rock solidifies, any potassium-40 that is present continues to decay, and the argon-40 that is produced cannot escape from the rock.
Thus, geologists use potassium-argon dating to measure the age of volcanic rocks.