Ordinary dating method
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.One we have dated a sufficient number of rocks and measured the orientation of the magnetism they contain, we can build up a picture of how the position or apparent position of the poles over time.So if we are then faced with a rock the date of which we do not know, then we do know (of course) the latitude and longitude at which we found it, and we can measure the orientation of its magnetism, and so we can look at the global picture we've built up of continental drift, and so figure out when the rock must have formed in order to have its magnetism oriented in just that direction.
There are well-known methods of finding the ages of some natural objects.
In this article we shall discuss how we can use the paleomagnetism in rocks to attach dates to them (paleomagnetic dating).
The reader may find it useful to go back and read the main article on paleomagnetism before continuing.
So if we are presented with an undated rock, and we find a really distinctive pattern of paleomagnetic reversals within it, we may be able to identify the one time at which such a sequence of magnetic reversals took place.
The reader will observe that it is necessary to be able to date some rocks, in fact a lot of rocks, before paleomagnetic dating can be brought into play.
(removal of material by solution) of the host substance with a suitable chemical reagent; the leaching process allows the etched fission-track pits to be viewed and counted under an ordinary optical microscope.