Carbon Dating I While alive, every being has a constant ratio of C(14) to C(12) –Cause: absorption from the atmosphere cosmic rays transform N(14) to C(14) –N(14) + N --> C(14) + P the ratio of C(14) to other forms of carbon remains constant during the lifetime of the object studied. N n C

Carbon Dating II When Dead, no more absorption of carbon takes place –the C(14) begins its decay to N(14) C(14) --> N(14)+ e hence the ratios of C(12) to C(14) change this change can be measured by the rate of nuclear activity C(14) has a half-life of only 5730 years, so only very young things can be measured (~50000 yrs.)

Carbon Dating III –Inaccuracies: the sun is not constant in its output many species do not attain carbon from the atmosphere, etc. –How to counteract the inaccuracies tree rings, ice core samples fine-tune the model

ourseware Potassium-Argon Dating Argon gas in volcanic samples is measured –Molten rock releases all argon initially present –Argon is then formed by the decay of potassium K(40) + e ---> Ar(40) + e

Potassium-Argon Dating II –Only very small amounts are found, which is the reason the K is not measured directly –The argon is measured by mass spectometry the ratio of potassium to argon gives a date –Objects as old as 4.5 billion years have been measured