Dating a rock
Dating a rock - ebony chat and dating sites
Using the basic ideas of bracketing and radiometric dating, researchers have determined the age of rock layers all over the world.This information has also helped determine the age of the Earth itself.
We can also construct a Concordia diagram, which shows the values of Pb isotopes that would give concordant dates.
But this sediment doesn't typically include the necessary isotopes in measurable amounts.
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.
To determine the ages of these specimens, scientists need an isotope with a very long half-life.
Other minerals that also show these properties, but are less commonly used in radiometric dating are Apatite and sphene.
If a zircon crystal originally crystallizes from a magma and remains a closed system (no loss or gain of U or Pb) from the time of crystallization to the present, then the Discordant dates will not fall on the Concordia curve.The Concordia curve can be calculated by defining the following: ).Zircon has a high hardness (7.5) which makes it resistant to mechanical weathering, and it is also very resistant to chemical weathering. Chemically, zircon usually contains high amounts of U and low amounts of Pb, so that large amounts of radiogenic Pb are produced.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.Other techniques include analyzing amino acids and measuring changes in an object's magnetic field.