Dating method in geology


As radioactive Parent atoms decay to stable daughter atoms (as uranium decays to lead) each disintegration results in one more atom of the daughter than was initially present and one less atom of the parent.The probability of a parent atom decaying in a fixed period of time is always the same for all atoms of that type regardless of temperature, pressure, or chemical conditions. The time required for one-half of any original number of parent atoms to decay is the half-life, which is related to the decay constant by a simple mathematical formula.Local relationships on a single outcrop or archaeological site can often be interpreted to deduce the sequence in which the materials were assembled.This then can be used to deduce the sequence of events and processes that took place or the history of that brief period of time as recorded in the rocks or soil.For example, the presence of recycled bricks at an archaeological site indicates the sequence in which the structures were built.Similarly, in geology, if distinctive granitic pebbles can be found in the sediment beside a similar granitic body, it can be inferred that the granite, after cooling, had been uplifted and eroded and therefore was not injected into the adjacent rock sequence.Although with clever detective work many complex time sequences or relative ages can be deduced, the ability to show that objects at two separated sites were formed at the same time requires additional information.



These include some that establish a relative chronology in which occurrences can be placed in the correct sequence relative to one another or to some known succession of events.The radioactive parent elements used to date rocks and minerals are: Radiometric dating using the naturally-occurring radioactive elements is simple in concept even though technically complex.If we know the number of radioactive parent atoms present when a rock formed and the number present now, we can calculate the age of the rock using the decay constant.Most people think that radioactive dating has proven the earth is billions of years old.

After all, textbooks, media, and museums glibly present ages of millions of years as fact.

All rocks and minerals contain long-lived radioactive elements that were incorporated into Earth when the Solar System formed.