Radiometric dating

Radiometric dating is the way we find the age of a rock that has unstable isotopes. we find the half-life to find the ratio of parent atoms to daughter atoms.

e.g's of radiometric dating

K^40 -> Ar^40   This is used in sedimentry and metamorphic rocks  halflife= 1260ma

Uranium-238 -> lead-206   This is used to find the age of igneous rocks halflife= 4500ma

Rb^87 -> Sr^87   This is used in very old igneous rocks - very long halflife = 50,000ma 



Problems of radiometric dating 

• Sedimentry- hard to date-> they erode easily, contain different minerals, layed down different times (Diachronus) and they need the mineral glauconite. 
• Argon is a gas so its almost impossible to find out the age in K^40 dating
• There is a margin of error in the dating-  +- 15ma
• Matamorphic - not a closed system. when it melts the time clock resets back to zero