Radioactive Dating

Amount of ParentIsotope Present

Amount of Daughter

Isotope PresentDecay

DecayAmount of

ParentIsotope Present

Amount of Daughter

Isotope Present

Will DECREAS

E

DecayAmount of

ParentIsotope Present

Amount of Daughter

Isotope Present

Will DECREAS

E

DecayAmount of

ParentIsotope Present

Amount of Daughter

Isotope Present

Will DECREAS

E

Will INCREAS

E

DecayAmount of

ParentIsotope Present

Amount of Daughter

Isotope Present

Will DECREAS

E

Will INCREAS

E

Ratio of: will INCREASEINCREASE

Daughter IsotopeParent Isotope

Ratio of: will INCREASEINCREASE

Daughter IsotopeParent Isotope

Good to 50 000 years

Good to 5 billion years

Earth’s atmosphere contains the element carbon, mainly in the form of carbon dioxide (CO2).Most of the carbon in the atmosphere consists of the stable isotope carbon–12 , but a very small fraction is a radioactive isotope called carbon–14 .The ratio of in the atmosphere has been relatively constant for the last 50 000 years.

126C

14 126 6C / C

146C

Earth’s atmosphere contains the element carbon, mainly in the form of carbon dioxide (CO2).Most of the carbon in the atmosphere consists of the stable isotope carbon–12 , but a very small fraction is a radioactive isotope called carbon–14 .The ratio of in the atmosphere has been relatively constant for the last 50 000 years.

126C

14 126 6C / C

146C

Earth’s atmosphere contains the element carbon, mainly in the form of carbon dioxide (CO2).Most of the carbon in the atmosphere consists of the stable isotope carbon–12 , but a very small fraction is a radioactive isotope called carbon–14 .The ratio of in the atmosphere has been relatively constant for the last 50 000 years.

126C

14 126 6C / C

146C

Earth’s atmosphere contains the element carbon, mainly in the form of carbon dioxide (CO2).Most of the carbon in the atmosphere consists of the stable isotope carbon–12 , but a very small fraction is a radioactive isotope called carbon–14 .The ratio of in the atmosphere has been relatively constant for the last 50 000 years.

126C

14 126 6C / C

146C

Carbon from the

Environment

While they are still alive, the ratio of remains the same as it is in the environment.

14 126 6C / C

When an organism dies, it stops getting fresh carbon from the environment.

Remainsas it is

126C

Remainsas it is

126C

Decreases as it decays

146C

As the object gets older, the ratio of gradually decreases over time.

14 126 6C / C

As the object gets older, the ratio of gradually decreases over time.

14 126 6C / C

Carbon–14 nuclei undergo beta decay:144 07 1

16 N eC

144 07 1

16 N eC

144 07 1

16 N eC

144 07 1

16 N eC

144 07 1

16 N eC

144 07 1

16 N eC

5730 y

144 07 1

16 N eC

5730 y

50% of its original

carbon–14 will

still be present

144 07 1

16 N eC

5730

y

A rib-bone from an archeological site was analyzed. By measuring the ratio of in the sample and comparing it to that in the environment, archeologists calculated that 12.0% of its original remained. How old is the bone?

14 126 6C / C

146C

12.0%12.0

%

12.0%

17 500 y

17 500 y

17 500 years old