Complex sentence: Their isotopic concentration in a natural rock sample depends on the presence of other elements: for example, the relative amount of lead-208 can range from 52.4% in normal samples to 90% in thorium ores.
Split into simpler sentences: Their isotopic concentration in a natural rock sample depends on the presence of other elements. For example, the relative amount of lead-208 can range from 52.4% in normal samples to 90% in thorium ores.