Radioactive dating of rocks

P., 1970, A critical examination of radioactive dating of rocks.

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A relative age simply states whether one rock formation is older or younger than another formation.The Geologic Time Scale was originally laid out using relative dating principles.Numerical dating, the focus of this exercise, takes advantage of the "clocks in rocks" - radioactive isotopes ("parents") that spontaneously decay to form new isotopes ("daughters") while releasing energy.For example, decay of the parent isotope Rb-87 (Rubidium) produces a stable daughter isotope, Sr-87 (Strontium), while releasing a beta particle (an electron from the nucleus).("87" is the atomic mass number = protons + neutrons.

Numerical ages have been added to the Geologic Time Scale since the advent of radioactive age-dating techniques. In theory, the age of any of these minerals can be determined by: 1) counting the number of daughter isotopes in the mineral, and 2) using the known decay rate to calculate the length of time required to produce that number of daughters.

It illustrates how the amount of a radioactive parent isotope decreases with time. For example when 42% of the parent still remains, 1.23 Half-Lives of time has passed.

This amount is a percentage of the original parent amount. Parent Decay and Daughter Growth Curves The half-life of U-235 decaying to Pb-207 is 713 million years.

Note that this half-life can be obtained from the graph at the point where the decay and growth curves cross.

Determine the half-lives for the other three isotopes and enter your estimate into the text fields below each graph.

Note the differences in scale between the various graphs Radiocarbon Dating The radiocarbon dating method was developed in the 1940's by Willard F.