A minimum age is the youngest the object can possibly be.

A maximum age is the oldest the object can possibly be. But they obviously have to have been made first, so 1920 is the maximum age of the burial.

In calculus terms, we write: d N(t)/dt = -K * N(t) or d N(t)/N(t) = -K dt The minus sign means that each decay decreases the total number of atoms.

Integrating both sides, we get: ln N(t) = -Kt C C is the constant of integration that we can often ignore, but not here.

If you don't have minerals with those elements, you can't date the rock.

In particular, quartzites and carbonate rocks almost always don't have enough to permit dating.

Sedimentary rocks are generally hard to date because common cements like silica don't have datable radioisotopes, and minerals like glauconite that are common in sedimentary rocks are very prone to resetting.

Let t stand for time and N(t) stand for the number of atoms at time t .

Crystallization of a mineral is a good way to close a system. Any disturbance of the system effectively resets the clock to zero by allowing decay products to escape or reshuffling the abundances of elements.

Weathering and metamorphism are the two most common ways to disturb a system.

Rubidium-strontium dating is more robust, and uranium-lead dating can survive fairly significant metamorphism without resetting.

If a system gains or loses isotopes in a predictable way, it may be possible to estimate the loss and correct the age.

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Back in the 1940s, the American chemist Willard Libby used this fact to determine the ages of organisms long dead.