Parent Decay and Daughter Growth Curves Radiocarbon Dating Dating Rocks with the Rb-Sr "Isochron" Method Getting a Rock Sample Ready for the Mass Spectrometer A Mass Spectrometer is used to Measure Isotopic Ratios A numerical (or "absolute") age is a specific number of years, like 150 million years ago.
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.
The minerals must contain Rb, which is a rather rare element.
Fortunately, Rb behaves chemically very much like the more common potassium (K), so that most K-bearing minerals contain a small amount of Rb. Sample Selection A geologist collects a fresh, unweathered hand sample for age dating.
Understanding the isochron diagram is the key to determining the age of a rock using the Rb-Sr method.
Radiometric dating or radioactive dating is a technique used to date materials such as rocks or carbon, in which trace radioactive impurities were selectively incorporated when they were formed.
These materials are then used to prepare a "whole-rock" sample and several "mineral separate" samples.
The whole rock sample will yield the weighted average isotopic composition of all the minerals in the rock.
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.
The radiocarbon method is applied in many different scientific fields, including archeology, geology, oceanography, hydrology, atmospheric science, and paleoclimatology.