What is 210Pb?
210Pb, a radioactive isotope in the 238U decay chain, is continuously produced by the decay of atmospheric 222Rn gas. The 210Pb is transported in precipitation to the Earth’s surface where it adsorbs onto silicate particles, some of which become lacustrine sediment. This 210Pb decays because it is unsupported by 226Ra via 222Rn. Therefore in undisturbed sediment that has been deposited continuously, the 210Pb concentration decreases systematically with depth. Provided that the atmospheric flux is constant, the decay profile relates directly to the sedimentation rate and hence 210Pb can be used to date sediment up to c. 100 years old.