Carbon dating exam questions

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Carbon is naturally in all living organisms and is replenished in the tissues by eating other organisms or by breathing air that contains carbon.At any particular time all living organisms have approximately the same ratio of carbon 12 to carbon 14 in their tissues.A new sample of the same type of wood has a count of 16 c.p.m.g Answer outline and marking scheme for question: 2 a) The half-life of a substance is the time taken for its concentration to decrease by 50%.b) After 5600 years the count form the piece of new wood would drop to 8 c.p.m, after a further 5600 years it will drop to 4 c.p.m.

The half-life of a substance can be found by measuring the count-rate of the substance with a Geiger-Muller tube over a period of time.When an organism dies it ceases to replenish carbon in its tissues and the decay of carbon 14 to nitrogen 14 changes the ratio of carbon 12 to carbon 14.Experts can compare the ratio of carbon 12 to carbon 14 in dead material to the ratio when the organism was alive to estimate the date of its death.By plotting a graph of count-rate against time the half-life can be seen on the graph.This would also work if you plotted the number of parent atoms against time.

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