Absolute dating of rock layer below Free real cam
by isotope K/Ar in mica, especially in the crystalline rock: igneous and metamorphic rock.
On the other hand, the sedimentary rock (as I know) usually provide the time of formation by age range of fossil e.g. Is there any method to make it more specific like the crystalline one?
To determine the ages of these specimens, scientists need an isotope with a very long half-life.
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.
Fossils are generally found in sedimentary rock not igneous rock.
Sedimentary rocks can be dated using radioactive carbon, but because carbon decays relatively quickly, this only works for rocks younger than about 50 thousand years.
Fossils can't form in the igneous rock that usually does contain the isotopes.
Dinosaur bones, on the other hand, are millions of years old -- some fossils are billions of years old.
Fossils, however, form in sedimentary rock -- sediment quickly covers a dinosaur's body, and the sediment and the bones gradually turn into rock.
But this sediment doesn't typically include the necessary isotopes in measurable amounts.
The question should be whether or not carbon-14 can be used to date any artifacts at all? There are a few categories of artifacts that can be dated using carbon-14; however, they cannot be more 50,000 years old.
Carbon-14 cannot be used to date biological artifacts of organisms that did not get their carbon dioxide from the air.
This technique is widely used on recent artifacts, but educators and students alike should note that this technique will not work on older fossils (like those of the dinosaurs alleged to be millions of years old).