Radioactive dating of meteorites
Radioactive dating of meteorites - Free Online
Meteorites are among the oldest objects we know about - formed about 4.5 billion years ago. This article describes the principles and methods used to make that determination.There are well-known methods of finding the ages of some natural objects.
When a tree is cut down, these periods are exhibited in a cross section of the trunk in the form of rings.The use of 14C in meteorite dating is solely based on its production by cosmic rays (and for terrestrial samples, with its production in the atmosphere).26Al and some other nuclides not mentioned are also used in this way.Thus, although "extinct", these nuclides are present in meteorites, but produced by a more recent process.These ions are accelerated in an electric field through collimating slits and subject to a magnetic field which causes the ions to follow a curved path. By adjustment of the strength of the magnetic field and suitable placement of an ion collector, the different isotopes can be measured with precision.There are some things that affect these measurements.
Thermal processes that may occur during meteorite impact in the lifetime of the specimen can reset some of the atomic clocks, mixing components and releasing important gases such as "You refer to extinct nuclides 14C, 26Al, and 129I.
Only the latter two "extinct" nuclides are used in dating.
Simply counting the number of rings will give one a fairly good idea of the age of the tree.
Periods of heavy rain and lots of sunshine will make larger gaps of growth in the rings, while periods of drought might make it difficult to count individual rings. When a given quantity of an isotope is created (in a supernovae, for example), after the half-life has expired, 50% of the parent isotope will have decomposed into daughter isotopes.
After the second half-life has elapsed, yet another 50% of the remaining parent isotope will decay into daughter isotopes, and so on.
For all practical purposes, the original isotope is considered extinct after 6 half-life intervals. A small portion of a meteorite is vaporized in the device forming ions.