Difference between relative dating and radiometric dating
Absolute dating(also known as radiometric dating) is based by the measurement of the content of specific radioactive isotopes of which the "half time" is known.Half time is the time needed for half of a given quantity of an isotope to decay in its byproducts.
They use absolute dating methods, sometimes called numerical dating, to give rocks an actual date, or date range, in number of years.The table below shows characteristics of some common radiometric dating methods.Geologists choose a dating method that suits the materials available in their rocks. Measuring isotopes is particularly useful for dating igneous and some metamorphic rock, but not sedimentary rock.For example, the decay of potassium-40 to argon-40 is used to date rocks older than 20,000 years, and the decay of uranium-238 to lead-206 is used for rocks older than 1 million years.Radiocarbon dating measures radioactive isotopes in once-living organic material instead of rock, using the decay of carbon-14 to nitrogen-14.Comparing the quantity of the parent form and the byproduct will give a numerical value for the age of the material containing such isotopes.
Example include carbon14-nitrogen, uranium-led, uranium-thorium. Relative dating instead allows for identifying the sequential order of geological events one relative to the other.
When ‘parent’ uranium-238 decays, for example, it produces subatomic particles, energy and ‘daughter’ lead-206.
Isotopes are important to geologists because each radioactive element decays at a constant rate, which is unique to that element.
Sedimentary rock is made of particles derived from other rocks, so measuring isotopes would date the original rock material, not the sediments they have ended up in.
However, there are radiometric dating methods that can be used on sedimentary rock, including luminescence dating.
Each original isotope, called the parent, gradually decays to form a new isotope, called the daughter.