Sentence:  Other rare elements, like <WSD>neodymium</WSD>, exist in more than one isotopic form, the ratios of which can provide a measure of the depth from which the flow material may ultimately have been derived. 
Meaning of the word marked with <WSD> tags:  A chemical element ("symbol" Nd) with an atomic number of 60: a hard, slightly malleable silvery metal that quickly tarnishes in air and moisture.