How does relative dating work compared to isotopic dating?
Specifically, the relative amounts of their constituent elements shift in a mathematically predictable way thanks to a phenomenon called radioactive decay. This in turn relies on knowledge of isotopes, some of which are radioactive (that is, they spontaneously emit subatomic particles at a known rate).
What is the difference between relative dating and stratigraphy?
The method of reading the order is called stratigraphy (layers of rock are called strata). Relative dating does not provide actual numerical dates for the rocks. Next time you find a cliff or road cutting with lots of rock strata, try working out the age order using some simple principles:
What are the assumptions of isotopic dating?
An important assumption that we have to be able to make when using isotopic dating is that when the rock formed none of the daughter isotope was present (e.g., 40 Ar in the case of the K-Ar method).
How do you select isotopes for dating rocks?
In dating rocks, we need to select an isotope pair with a parent isotope that has a reasonable half-life. This means that the half-life must not be too short or too long. If the half-life is too short, then most of the parent isotope will have decayed to form the daughter isotope.
Why is potassium feldspar a good isotopic dating candidate?
Figure 8.4.2 Crystals of potassium feldspar (pink) in a granitic rock are candidates for isotopic dating using the K-Ar method because they contained potassium and no argon when they formed. Why can’t we use isotopic dating techniques to accurately date sedimentary rocks?
How do you determine the age of an isotope?
The abundances of parent and daughter isotopes in a sample can be measured and used to determine their age. This method is known as radiometric dating. Some commonly used dating methods are summarized in Table 1. The rate of decay for many radioactive isotopes has been measured and does not change over time.