Methods for dating the earth

The changing ratio of C-12 to C-14 indicates the length of time since the tree stopped absorbing carbon, i.e., the time of its death.Obviously, if half the C-14 decays in 5,730 years, and half more decays in another 5,730 years, by ten half-lives (57,300 years) there would be essentially no C-14 left.From the fragments, scientists calculated the relative abundances of elements that formed as radioactive uranium decayed over billions of years.

In reality, its measured disequilibrium points to just such a world-altering event, not many years ago.Thus the ratio of stable C-12 to unstable C-14, which is known in today's open environment, changes over time in an isolated specimen. As long as the tree lives, it absorbs carbon from the atmosphere in the form of carbon dioxide, both C-12 and C-14.Once the tree dies, it ceases to take in new carbon, and any C-14 present begins to decay.Furthermore, the assumptions on which it is based and the conditions which must be satisfied are questionable, and in practice, no one trusts it beyond about 3,000 or 4,000 years, and then only if it can be checked by some historical means.The method assumes, among other things, that the earth's age exceeds the time it would take for C-14 production to be in equilibrium with C-14 decay.