Download Absolute Dating with Radioactivity:

Absolute Dating with Radioactivity:
Definition: Radiometric Dating –
-some atomic nucleus are stable; others are not
-in unstable nucleus, the nuclear force that holds protons together is not strong
enough
to overcome the repulsive electrical forces between protons
-these nuclei are radioactive
-radioactive nucleus emit groups of particles (i.e. protons, neutrons)
-this process is called radioactive decay
Definition: Half-Life –
-when uranium is incorporated into a mineral that crystallizes from magma, there
is no lead present (radiometric “clock” set to 0)
-when uranium decays, lead begins to form
-amount of lead in the mineral when uncovered AND the rate at which uranium
decays (or half-life) can determine when the mineral formed from magma
-carbon is present in all forms of life
-amount of carbon tested in fossil remains to determine how long it has been
since organism died
Examples of Radioactive Elements and their Half-Lives:
 Uranium-238
 Uranium-235
 Rubidium-87
 Carbon-14
-because some radioactive elements have very long half-lives, radiometric
dating has shown that Earth has a long history
-Hutton’s theory gained support through radiometric dating because it shows that
structures are formed over millions of years (Uniformitarianism)
-disadvantage of absolute dating:
-ex: a sedimentary rock may contain weathered rock particles from differentaged rocks; geologists use volcanic ash layers next to sedimentary rock to gauge
absolute age (law of superposition)