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- Isotopes can be used as tracers - Isotopes can be used as energy source - Isotopes are used for radioactive dating - Isotopes are used…
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In most cases, we cannot use isotopic techniques to directly date fossils or the sedimentary rocks they are found in, but we can constrain their ages by dating igneous rocks that cut across sedimentary rocks, or volcanic ash layers that lie within sedimentary layers.
Isotopic dating of rocks, or the minerals in them, is based on the fact that we know the decay rates of certain unstable isotopes of elements and that these rates have been constant over geological time.
It has a half-life of 1.3 billion years, meaning that over a period of 1.3 Ga one-half of the Figure 8.14 The decay of 40K over time.
Each half-life is 1.3 billion years, so after 3.9 billion years (three half-lives) 12.5% of the original 40K will remain.
An example is shown in Figure 8.16; radiocarbon dates from wood fragments in glacial sediments have been used to estimate the time of the last glacial advance along the Strait of Georgia.
Figure 8.16 Radiocarbon dates on wood fragments in glacial sediments in the Strait of Georgia [SE after Clague, J, 1976, Quadra Sand and its relation to late Wisconsin glaciation of southeast British Columbia, Can.
Over time, the Ar remain embedded within the crystal, unless the rock is subjected to high temperatures after it forms.
The sample must be analyzed using a very sensitive mass-spectrometer, which can detect the differences between the masses of atoms, and can therefore distinguish between Ar in the case of the K-Ar method).
Some of the other important pairs are listed in Table 8.2, along with the age ranges that they apply to and some comments on their applications.Tags: Adult Dating, affair dating, sex dating