What type of rock is best for radiometric dating
Some of the isotopes used for this purpose are uranium-238, uranium-235 and potassium-40, each of which has a half-life of more than a million years.Unfortunately, these elements don't exist in dinosaur fossils themselves.These layers are like bookends -- they give a beginning and an end to the period of time when the sedimentary rock formed.By using radiometric dating to determine the age of igneous brackets, researchers can accurately determine the age of the sedimentary layers between them.For example, by using a laser, researchers can measure parent and daughter atoms in extremely small amounts of matter, making it possible to determine the age of very small samples [source: New Scientist]. Wiens has a Ph D in Physics, with a minor in Geology.
To determine the ages of these specimens, scientists need an isotope with a very long half-life.
Sedimentary rock on the other hand consists of sedimentary particles which were removed and deposited somewhere else by some sort of fluid (generally wind and water).
The sedimentary particles predate the rock which they form.
This technique is generally used to date igneous and metamorphic rock, which are rocks that were once melted due to extreme heat and pressure.
Radiometric dating determines how long ago the liquid rock solidified into solid rock.