Radiometric Dating Carbon Dating

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Radiometric Dating method of estimating the relative age of geological artifacts utilizing the half-life of known isotopes “estimate” “relative age” “approximation”

Half-life time it takes for ½ of an isotope to decay different isotopes have different half-lives

Carbon-14 Dating Carbon (C) has three naturally occurring isotopes. Both C-12 and C-13 are stable, but C-14 decays by very weak beta decay to nitrogen-14 with a half-life of approximately 5,730 years. Naturally occurring radiocarbon is produced as a secondary effect of cosmic-ray bombardment of the upper atmosphere. Plants transpire to take in atmospheric carbon, which is the beginning of absorption of carbon into the food chain. Animals eat the plants and this action introduces carbon into their bodies.

After the organism dies, carbon-14 continues to decay without being replaced. To measure the amount of radiocarbon left in a artifact, scientists burn a small piece to convert it into carbon dioxide gas. Radiation counters are used to detect the electrons given off by decaying C-14 as it turns into nitrogen. The amount of C-14 is compared to the amount of C-12, the stable form of carbon, to determine how much radiocarbon has decayed, thereby dating the artifact.

Carbon-14 decays into Nitrogen Half-life = 5,730 years

Example #1: Carbon-Dating While unearthing the the remains of the ancient village Krakatoa in Indonesia, archeologist discovered discovered some broken clay pots fragments deep in the earth. It was estimated that 14% of the Carbon-14 remained in a 10 gram sample. Approximately how old is the clay pot fragment?

TIME (years) HALF – LIFEPERCENTAMOUNT g 15, g 211, g 317, g

Example #2: Carbon-Dating While mining for salt in south-central Kansas the salt diggers uncovered a fossilized wooden spoon in the earth. Upon analysis it was determined to contain roughly 5.8% of the relative C-14 composition. Assume that the original amount of C-14 was 60 grams. How old is the fossilized wooden spoon?

TIME (years) HALF – LIFEPERCENTAMOUNT g 15, g 211, g 317, g 422, g , g

Example #3: determining half life Mr. Brown was using radioactive P-32 (Phosphorous-32) to radiolabel genetic material used for research. He ordered 350 grams of P-32 (which has a half life of 14.5 days) on April 1 st. How much will be left at the end of May?

TIME (days) HALF – LIFEPERCENTAMOUNT g g g g g

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