Closed system radiometric dating
This method should also be applied only to minerals that remained in a closed system with no loss or gain of the parent or daughter isotope.Uranium-Lead Dating Uranium-Lead (U-Pb) dating is the most reliable method for dating Quaternary sedimentary carbonate and silica, and fossils particulary outside the range of radiocarbon.
At about 50 000 to 60 000 years, the limit of the technique is reached (beyond this time, other radiometric techniques must be used for dating).
The basic principle Carbon has three naturally occurring (n is a neutron and p is a proton) After formation the three carbon isotopes combine with oxygen to form carbon dioxide.
The carbon dioxide mixes throughout the atmosphere, dissolves in the oceans, and via C in the original sample will have decayed and after another 5568 years, half of that remaining material will have decayed, and so on.
In contrast to a method such as Radiocarbon dating, which measures the disappearance of a substance, K-Ar dating measures the accumulation of Argon in a substance from the decomposition of potassium.
Argon, being an inert gas, usually does not leech out of a mineral and is easy to measure in small samples.