Beryllium 7 dating
The lines crossing this mountainside above Lake Ohau are lateral moraines left behind as the glacier gradually lowered, and finally vanished at the end of the ice age.One of the best methods of dating these moraines is by measuring the concentration of the isotope beryllium-10 in the top surface of large boulders situated on them.Lake Ohau is one of several very large lakes in the Southern Alps that fill valleys once carved out by huge glaciers during the Ice Age.As the ice retreated, it left spectacular and classic landforms in its wake, including concentric lines of moraines, erratic boulders, 'U' shaped valleys and extensive outwash plains.
Radiometric dating is a method of determining the age of an artifact by assuming that on average decay rates have been constant (see below for the flaws in that assumption) and measuring the amount of radioactive decay that has occurred.
(Since they are produced by a cosmic ray interaction, all these products are known as cosmogenic nuclides).
With time, a freshly exposed rock surface will gradually accumulate more and more beryllium-10 so that by careful measuring of its concentration in a boulder, the length of time that it has been exposed can be calculated.
Recognizing this problem, scientists try to focus on rocks that do not contain the decay product originally.
For example, in uranium-lead dating, they use rocks containing zircon (Zr Si O Zircon and baddeleyite incorporate uranium atoms into their crystalline structure as substitutes for zirconium, but strongly reject lead.