Absolute Dating

1. Absolute Dating Radioactive dating of rocks

2. Absolute Dating • A method used by geologists to determine a rock’s age in years. • Uses the properties of atoms in rocks to find their ages.

3. Isotopes • Atoms of the same element can have different numbers of neutrons; the different possible versions of each element are called isotopes. • For example, the most common isotope of hydrogen has no neutrons at all; there's also a hydrogen isotope called deuterium, with one neutron, and another, tritium, with two neutrons. HydrogenDeuterium Tritium Neutrons = 0Neutrons = 1Neutrons = 2

4. How many isotopes can one element have? • There are "preferred" combinations of neutrons and protons, at which the forces holding nuclei together seem to balance best. • Light elements tend to have about as many neutrons as protons; heavy elements tend to need more neutrons than protons in order to stick together. • Atoms with a few too many neutrons, or not quite enough, can sometimes exist for a while, but they're unstable.

5. Unstable atoms are radioactive: their nuclei change or decay by spitting out radiation, in the form of particles or electromagnetic waves. • During radioactive decay, the atoms of one element break down to form atoms of another element.

6. Half Life • The amount of time it takes for half of the atom to decay. • Example: Half-life of carbon-14 • The half-life of carbon-14 atoms is 5730 years. So it will take 5730 years for half the carbon-14 atoms in an object to decay into nitrogen-14 atoms.

8. Geologists use radioactive dating to determine the absolute age of rocks.