ABSOLUTE AGE:Measurements of natural

radioactivity in rocks have allowed scientists to understand the numerical age of an object in years

- When an organism dies, the elements in that organism will decompose because they are UNSTABLEelements such as C14, K40,

U238, Rb238The above elements decay into other elements that are stable

C14 decays into N14 U238 decays into Pb206

DECAY PRODUCT:A radioactive isotope will break down naturally into the lighter element

C-14(unstable) decays into N-14(stable)

HALF LIFE:

The time required for half of an elements atoms in a sample to change to the decay product

*front page of reference tables

EX: half of C-14 N14 in 5.7x 103 (5700 years)

-Depending on the original element, varying numbers of years are required to decay it

For Example:-It takes 5.7x 103 years (5700)

for half of a sample of C14 to decay into N14

-It takes 4.5x 109 years (4,500,000,000) for half of a sample of U 238 to decay into Pb 206

ISOTOPES:-Chemical elements often have several forms.

EX:Carbon-14 has 6 protons and 8 neutrons in its nucleus.Carbon-12 has 6 protons and 6 neutrons in it’s nucleus

C-14 has too many neutrons in its nucleus so it is said to be radioactive. C-12 is the stable isotope.

* C14 is not good to use if dating fossils older than 50,000 years because too much material has been decayed by then

* C14 has an extremely short half life

* C14 breaks down really fast

SELECTING THE BEST RADIOACTIVE ELEMENT TO DATE A SAMPLE

-sample needs to contain a measurable quantity of the radioactive element.-C-14 because of it’s short half life, (5.7x103) can date samples no older than about 50,000 years.*This is because so many half lives

have passed that there is not enough of the original material to be measured. Too much has decayed